|| MOFGA's 2007 Pest Reports - Compiled by Eric Sideman, PhD
|July 16 | July 3 | June 19 | June 4 | May 25 | May 7|
|POTATO LEAF HOPPER: The potato leaf hopper is wide spread now in Maine on potatoes, beans and strawberries. Check the July 3 Pest Report for details.|
BLACK ROT OF BRASSICAS: Black rot is a potentially very destructive disease that effects all Brassica vegetables. It can appear on plants at any growth stage. The symptom on true leaves is yellow, vaguely V-shaped areas that sort of follow leaf veins. As the lesion expands the tissue wilts and eventually becomes brownish and dry. The infection may move up or down the plant in the vascular tissue and such a systemic infection may produce scattered yellow lesions on leaves anywhere on the plant. Veins of infected leaves turn black.
Black rot is caused by a bacteria called Xanthomonas campestris. The pathogen survives from season to season on seed and in diseased crop residue. It also can survive in soil for a month or two. Very few infected seeds can lead to a crop failure as the disease can spread very quickly under the right conditions in splashing water, wind, insects and farm workers. Long distance spread is by seed and transplants.
Key to avoiding the disease is to use clean seed. A hot water treatment is effective but it needs to be done carefully (see the Resource Guide for Organic Insect and Disease Management for details, which is available from MOFGA or at https://www.nysaes.cornell.edu/store/catalog/.
Crop rotation is important. If you have this problem avoid planting Brassicas for 2 years in that field and be sure to manage Brassica weeds. Sanitation is also important. Destroy crop residue after harvest. If the disease is present do not plant a successive crop into that soil. Cull piles should be composted or destroyed. Do not use manure from livestock that have been fed diseased Brassicas on fields intended from Brassica crops.
SWEET CORN SITUATION: (Reprinted from UMaine Sweet Corn IPM Newsletter No. 2). Corn planted on early ground and through plastic mulch in southern Maine is now in silk. Many stands around the state are uneven, and growers have been watering as much as possible to keep up growth through the recent dry spell. Late plantings are in whorl to pre-tassel. Fertilizer burn from sidedressing has been noticeable in some fields, probably worse this year due to the lack of water. Once corn starts silking we need to be even more alert to pest issues. All three of the major insect pests can enter the silk channels and feed on the ears without leaving visible damage on the plant. Therefore, we must respond to moth captures in pheromone traps to be able to adequately protect the crop.
European Corn Borer: Pheromone trap catches indicate that we continue to experience a significant flight of European corn borer moths, with over 300 caught in one trap last week. We are finding more larvae feeding on the foliage and tassels this week. From the pre-tassel stage to silking stages, the control threshold is 15% of plants showing damage. Sprays during the pre-tassel stage reduce the opportunity for larvae to move into the stalks and ears of the plant. Several fields were over threshold for feeding injury this week for pretassel to silking corn, and sprays were recommended. When corn reaches the silk stage sprays may be based on the number of corn borer moths caught in pheromone traps rather than just feeding injury. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught in a week in a field with silking corn, a spray will be recommended. Sprays to protect silking corn from European corn borer were recommended in Auburn, Dayton, New Gloucester, Nobleboro and Wayne.
Corn Earworm: We continue to catch a few corn earworm moths around the state, mostly as single moths in traps, and/or in fields that are not yet silking. Therefore we have not yet recommended a spray for earworm in any field, but we will be keeping a close eye on this in the coming weeks. The risk of an infestation will increase greatly if our weather patterns change to bring fronts up from the southern states, which tend to carry the moths with them. The arrival of this pest is only aconcern for corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm.
Fall Armyworm: We caught one fall armyworm in a New Gloucester pheromone trap this week. While this is not yet cause for alarm, it may indicate that we can expect an early arrival of this pest. We have not yet found any feeding injury from larvae. Pheromone trap catches will indicate if this pest presents a threat to silking corn, however corn will usually be on a spray program for corn earworm when fall armyworm is present, and both insects would be controlled.
IMPORTED CABBAGE WORM: The white butterflies are flying all around the cabbage family plants now and laying eggs, and the larvae (green caterpillars) are chewing holes in the leaves. If you have heading broccoli you must know your customers because some folks are really turned off by the critters floating to the top of the water in the cooking pot. You may want to spray that even though the crop is beyond risk.
This pest overwinters as a pupa and there are 3-4 generations per year. This means that once you start seeing the butterfly you should start scouting for the caterpillar in about a week. Bt (Dipel 2X or Dipel DF) or Entrust work very well in controlling the caterpillar. None of these materials lasts in the field and so should only be sprayed when the caterpillars are there in large enough numbers to warrant it.
Destroy or bury crop residue after harvest so as not to allow the caterpillars to continue to feed and complete their life history and thus a larger second generation.
BACTERIAL DISEASES OF TOMATO - UPDATE 2007: (Modified from a report in from the Umass Vegetable Newsletter). Three bacterial diseases affect tomato crops-Bacterial Spot (Xanthomonas campestris pv. vesicatora), Bacterial Speck (Pseudomonas syringae pv tomato), and Bacterial Canker (Clavibacter michiganensis pv michiganensis).
Bacterial spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is present wherever tomato and peppers are grown. In general, Xanthomonas pathovars have narrow host ranges. Xcv consists of different strains that vary in their pathogenicity to tomato, pepper, and solanaceous weeds. The bacterium is able to survive on tomato volunteers and can overwinter in diseased plant debris. Seed is an important mechanism for survival and dissemination of Xcv. Disease development is favored by temperatures between 80 and 90 F and by heavy rainfall. The bacterium is spread by wind-driven rain, workers, farm machinery, and aerosols. It penetrates through stomates and wounds created by insects, wind-driven sand, and tools. Xcv affects all aboveground plant parts. On leaves, the spots are generally brown, circular, and water-soaked. Bacterial spot lesions do not have concentric zones or a prominent halo. When conditions are optimal for disease development, spots can coalesce to form long, dark streaks. A general yellowing may appear on foliage with many lesions giving the plants a scorched appearance, and the plants may exhibit severe epinasty. Only green tomato fruit is susceptible to infection and lesions are quite distinct, beginning as minute, slightly raised blisters with a halo that resemble the birds-eye spot caused by Clavibacter michiganense (bacterial canker). As lesions enlarge, they loose their halo and become brown, raised, and scab-like. Lesions on ripe pepper fruit may be scab-like or sunken.
Bacterial speck occurs on tomato not pepper. It is a cosmopolitan disease, generally of minor concern, favored by low temperatures and high moisture. The bacterium Pseudomonas syringae pv tomato causes a fruit spot and foliage blight. This bacterium is also seedborne, spreads within fields in the same manner as bacterial spot, and may persist in weed species. Lesions on leaves are round and dark brown to black with a halo that develops with time. Spots may coalesce, killing large areas of tissue. On fruit, small (1/16 inch), dark spots or specks develop with the tissue around them often more intensely green than unaffected areas.
Bacterial canker (Clavibacter michiganensis pv michiganensis) is one of the most destructive tomato diseases in Massachusetts. Initial symptoms are the result of primary, systemic infection and first affect the lower leaves causing leaf curling, wilting, chlorosis, and shriveling. In advanced stages, the pathogen spreads throughout the plant and causes poor growth, wilt, and plant death. Foliage throughout the canopy wilts, yellows, turns brown, and collapses. Stems can split resulting in open breaks or cankers and stems break easily. Secondary infections occur from rain splash onto foliage, stems, and fruit. Spots occur on green fruit and are very characteristic: white to yellow spots, 3-4 mm with raised brown centers ("bird¹s eye spots").
Three key principles for preventing losses to bacterial diseases are:
1. Start with certified, disease-free seed or treat seed with hot water, hydrochloric acid, calcium hypochlorite, or other recommended materials. See the fact sheet entitled, Preventing Bacterial Diseases of Vegetables with Hot-water Seed Treatment for further details at www.umassvegetable.org.
2. Control bacterial populations that may be present on the leaf surface of transplants in the greenhouse. Young transplants may not display symptoms of bacterial diseases. Inspect and remove suspect transplants. Lower the water
pressure in irrigation equipment to avoid damaging leaves. Avoid the practice of mowing transplants to regulate transplant height.
3. Plant into a clean field. Promptly incorporate crop debris after harvest. Rotate to a non-host crop before returning to tomato and do not allow volunteer tomato or weed hosts to survive.
Research at the University of Michigan has shown that: 1) the pathogen can move readily from infected plants onto clean plants in the course of regular greenhouse activities, and 2) carryover in the greenhouse from one season to the next may not be as important as was once thought. In one experiment, seedlings that carried systemic infections with bacterial canker were placed in known locations in a grid of transplants in the greenhouse. Watering was from hand-held sprinklers no special precautions were taken to prevent disease spread. Plants nearest the infected plants developed bacterial canker symptoms (wilting) and died in the greenhouse. Many other plants showed no symptoms in the greenhouse, but the bacteria could be found residing on the surface of the leaves. When these healthy-looking plants were set out in the field, they developed symptoms during the season and the yield losses were serious. This type of infection -- bacteria that enter from the surface of the leaf through natural leaf openings or wounds -- causes the ³marginal scorch² symptoms that are so common in Massachusetts. Once the bacteria enters the plant -- which could occur in the greenhouse or in the field -- it can take anywhere from 7 to 84 days for symptoms to appear.
If infected plants are present, the movement of bacteria from one plant to another during normal watering, handling, and ventilating activities occurs readily. Controlling the bacteria at this stage can prevent yield losses. Bacteria on the surface of transplants can be effectively controlled by sprays of copper hydroxide. Kocide DF is labeled for greenhouse use on tomato.
Avoid working in fields when bacterial diseases are present and the fields are wet.
Rotate your tomatoes to a different field. Setting clean transplants into a field where infected tomato was grown the previous year will result in early infection and reduced yields. Bacteria survive in the field as long as there is any infected crop debris. They persist longer in debris on the surface than in buried debris. Plowing after harvest will help to speed up the decomposition. Keep each field out of tomato (and related crops such as potato and eggplant) for two to three years. Avoid using overhead sprinkler irrigation in the field. Use new stakes or stakes that have been cleaned and disinfected. Periodically and regularly sanitize tools such as clippers and pruning shears with an approved disinfectant during field operation.
Prevention is cost-effective. All of these tactics focus on prevention -- ensuring that disease-free plants go out into a ³clean² environment. Bacterial disease outbreaks in the field require regular sprays with a copper with limited success. Prevention strategies are both the least expensive and the most effective way to treat these diseases. -- Dr. Robert Wick, Dept of Plant, Soil & Insect Sciences, University of Massachusetts, M. Bess Dicklow, UMass Extension Plant Diagnostic Lab.
SCARAB BEETLE UPDATE: JAPANESE, ORIENTAL AND ASIATIC GARDEN BEETLES ARE ACTIVE: (Modified from a Report in the Umass Vegetable Newsletter). Japanese Beetles have emerged and are showing up in various crops and non-crop habitats. Oriental Beetles are also active and, though less damaging, may appear in vegetable fields as well. Asiatic Garden Beetles become evident mostly through their damage, because they feed at night. All species are feeding and starting to lay eggs now.
There are four species of scarab beetles that are common in New England turf, fruit and vegetable crops. These were all introduced to the US. Japanese beetles are the most common and widely distributed but Oriental and Asiatic Garden beetles are expanding their range and activity. Below are brief descriptions.
JAPANESE BEETLE adults are about half an inch long, with a metallic green head. The wings are shiny copper or bronze color, and there are a few tufts of white "fur" along the side of each wing when it is folded back over the body. The adults are active in daylight and feed on many different kinds of trees, fruit and flower crops. Fruit and ornamental plants are preferred, but beetles can congregate in vegetables also. In vegetables, adults can cause silk clipping in corn, and leaf damage in sweet basil, collards, other greens, green beans, eggplant, asparagus, rhubarb, and peppers. Though numbers may be high, there is no need to treat unless actual feeding damage is significant. In corn, if there are more than two Japanese beetles per ear and corn is less than 50% pollinated, an application may be warranted to reduce clipping and ensure adequate pollination.
ASIATIC GARDEN BEETLES are about half as long as a Japanese beetle adult, and somewhat more ³plump² or domed in appearance. They are reddish-brown or copper-colored. They often are found near roots of plants when one is weeding. Adults tend to cause more damage to vegetable crops than Oriental Beetle, but less than Japanese beetles. Because they feed at night, one may find damage without seeing the beetles. During the day they hide in the loose soil or mulch around the base of the plants. Scout with a flashlight at night, or sift through soil to find them. Larvae feed on beet, carrot, corn, lettuce, onion, Swiss chard and strawberry. Adults feed on carrot, beet, parsnip, pepper and turnip. One grower reported heavy beetle feeding on peppers that were held under row cover through the end of June: this could be the result of Asiatic garden beetles that emerged under the cover. He could not find beetles, only damage. Beware the events that occur under row cover while unsuspecting farmers are looking the other way!
ORIENTAL BEETLES fly at night, but are very active during the day as well. The beetles are smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. The pattern and color varies. Occasionally an individual will be almost all black or almost all gray. The antennae are branched and are quite striking if you take a close look. Oriental beetles have a long flight period through early August and are very mobile. Adults tend not to feed heavily in vegetable crop foliage. Grub damage may be worse in drought years and in weedy fields, but is not commonly a problem in vegetable fields and crops, though this is not well studied.
A fourth species may also be found: EUROPEAN CHAFERS, which are slightly larger than Japanese beetles and are a fairly dull brown or tan in color. They are night fliers but can be seen in large numbers just at sunset, when they congregate in large numbers in favorite trees (such as locust or willow). Adults are not foliage feeders and grubs are mostly a turf problem.
LIFE CYCLE. The life cycle of the Japanese beetle fits most of the species of grubs we encounter in New England, with minor variations depending on the species and the location. They have a one-year life cycle, with adults emerging from the soil in early July in most of Massachusetts (later farther north) to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). The first grubs usually appear around late July or early August and begin feeding on roots of grasses and other plants (especially corn). After about two weeks of feeding, the grubs molt to a second "instar", and feed for another three weeks. The grubs molt once more, to the "third instar" (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks. By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.
CONTROLS. There are not many controls for organic growers to choose from. Beneficial nematodes work fairly well on the grubs if there before the population explodes, but for vegetable grower the adults are the critters that cause most damage and they are good fliers so your control of grubs in your sod fields will not likely reduce the damage. Neem and pyrethrum offer fair control of the adults. - R. Hazzard, adapted from Pat Vittum, Turf Entomologist, UMass, Beth Bishop, Michigan State University, Michael Seagraves, Cornell Cooperative Extension, and Ann Hazelrig, University of Vermont
STRIPED CUCUMBER BEETLE: All over the Northeast, striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris on field edges and move rapidly into the field with the emergence of cucurbit crops and the onset of warm days. Densities can be very high, especially in non-rotated fields or close to last year's cucurbit crops. Adult feeding on cotyledons and young leaves can cause stand reduction and delayed plant growth. More importantly, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt. This disease overwinters within the beetle and is transmitted by contact of beetle feces with the open wounds in leaf tissue caused by beetle feeding. Bacteria multiply and block the vascular system of the plant, causing vines to wilt. This disease can be effectively managed only by preventing feeding by the beetle. Vine crops vary greatly in their susceptibility to wilt.
Early season infection. Pumpkin plants at the cotyledon and first 1-2 leaf stage are more susceptible to infection with bacterial wilt than older plants, and disease transmission is low after about the 4-leaf stage. Wilt development is strongly influenced by the dose of the pathogen that the plants receive. Typically, only a relatively small proportion (1-10%) of overwintering beetles carry the Erwinia pathogen and are able to infect plants. The higher beetle density during early plant growth, the more severe the incidence of wilt. Beetles that discover a host plant will release an aggregation pheromone that calls others to their spot. Groups of beetles feeding, wounding and defecating on a single plant are more likely to transmit disease, acquire the pathogen, and transmit it to other plants.
Thresholds and foliar controls. Beetle numbers should be kept low, especially before the 5-leaf stage. Crop rotation to a field at a distance from last year's cucurbits reduces beetle numbers significantly and may eliminate the need for controls. Beetle numbers tend to build up when vine crops are planted in the same or nearby fields year after year. Conventional IPM systems have relied on scouting frequently (at least twice per week) and treating after beetles colonize the field. To prevent bacterial wilt, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants in susceptible crops. This is a lower threshold than is needed to prevent significant foliar damage. Less wilt-susceptible crops will tolerate one or two beetles per plant without yield losses. Proper timing can be difficult: growers have to be ready to respond quickly in a very busy time of the season, and weather or field conditions can delay sprays. However, foliar sprays remain a viable option (see below).
Row covers are being used by many growers of curcubits to prevent early season attack by the cucumber beetle. Remember, the row covers need to be removed to weed periodically, and removed for the season when flowers appear to allow pollination.
Scouting and using foliar sprays: Look for signs of feeding on the underside of leaves, especially the cotyledons. Beetles are often found underneath leaves or in cracks in the soil. Check sets of 5 plants in at least five areas of the field (25 plants total), counting number of beetles on or near the plant. This can be done in about 15-20 minutes. Check field edges for hot spots. Beetles often colonize from field edges and numbers will be higher in the first rows near a woods or fallow area. Border treatments or border trap crops may help reduce infestation of the whole field. See the 2002-2003 New England Vegetable Management Guide for specific materials. (Don't have one? Call your local Extension office to order your copy).
When to spray? Controlling cucumber beetles in the cotyledon to 5 leaf stage is the only way to preventing bacterial wilt. For susceptible crops such as cucumber, summer squash and zucchini, muskmelon, gourds, and some winter squashes and pumpkins, lower thresholds are needed. Do not allow numbers to exceed 1 beetle per two plants. The time between first arrival of beetles and that threshold can be short, so keep an eye on fields once you see any beetles and spray within 24 hours of reaching threshold.
Controls: For organic growers, kaolin (Surround WP) provides an option. It is best applied by dipping seedlings before transplanting. Pyrethrin (Pyganic Crop Spray 5.0 EC) is another option but to me since it is a broad spectrum pesticide is muh less attractive. Use as a last resort only. Perimeter trap crops (see below) are another option. NOTE: available Rotenone products do not meet inert ingredient guidelines under the National Organic Program. For growers using Surround, here are some suggestions:
Most important is to clean up fields early in fall after harvest and reduce overwintering sites. -- Modified from a 2002 report by Ruth Hazzard
- Apply before beetles arrive. This acts as a repellent and anti-feedent so must be present before damage is done.
- If you are using transplants, apply before setting them out. This saves time and materials.
- With direct-seeded crops, apply as soon as seedlings emerge if beetles are active.
- Ensure good coverage of the foliage (it will look like it was sprayed with white latex paint), including, if possible, the undersides of leaves (not easy when cotyledons are close to the ground).
- Reapply after a heavy rain.
- When mixing, add the powder to water and allow it to settle slowly. Once the powder is fully wet, agitate gently. This reduces clumping. One approach is to mix a more concentrated slurry in a bucket and then add the slurry to the tank, as the dry powder could cake if added directly to the tank mix. Continuous agitation is needed.
- Although kaolin is safe in terms of skin exposure or ingestion, handlers should take precautions to avoid breathing the powder. Wear a respirator or mask when mixing and spraying.
PERIMETER TRAP CROPPING FOR CUCUMBER BEETLE MANAGEMENT: Trap crops are used to protect the main cash crop from a pest or complex of pests. The trap crop can be a different plant species, variety, or just a different growth stage of the same species as the main crop, as long as it is more attractive to the pests when they are present. Perimeter Trap Cropping involves planting the attractive plant species so that it completely encircles the main crop like fortress walls. A trap crop barrier on all sides is useful when it is necessary to protect the crop from a pest attack that may come from several or unknown directions. This technique works best against pests that tend to damage the crop along the edge of the field (at least initially) - such as striped cucumber beetle.
Perimeter Trap. Cropping functions by concentrating and/or killing the pest in the border area, while reducing pest numbers and disease spread on the unsprayed cash crop in the center and by preserving natural enemies. Perimeter Trap Cropping often eliminates the use of broad-spectrum pesticides on the cash crop, which helps preserve natural enemies and helps prevent resurgence of the primary pest population, secondary pest outbreaks and additional spraying to solve these "man-made" problems. Perimeter Trap Cropping often results in improved crop quality and dramatic pesticide savings. Less spraying usually translates into lower costs.
Blue Hubbard around yellow summer squash. In 2002, Connecticut researchers attempted to stop cucumber beetles and squash vine borers damage on summer squash using Blue Hubbard as a perimeter trap crop. Blue Hubbard was chosen because it is highly attractive to beetles, grows fast, and is not susceptible to bacterial wilt so it does not serve as a reservoir of wilt for the rest of the field. In the 2002 trials, over 94% of the cucumber beetles in the experiment were on plants in the perimeter. Beetle populations on the unsprayed main crop in the center were reduced by up to 95%. In addition, spraying the perimeter trap crop reduced squash vine borer infestation on the unsprayed summer squash within by 88%. Six commercial cucurbit growers successfully employed the technique in 2002. All the growers improved their pes control and reduced crop damage using Perimeter Trap Cropping, and all said they would continue to use trap crops in the future.
How to use perimeter trap cropping in yellow and green summer squash - or other vine crops. A number of growers in CT and MA are testing Perimeter Trap Cropping in summer squash and butternut this season. You may be interested in trying it, or come to summer twilight meetings to learn more about it. Here are some suggestions if you want to try it:
PTC can also be used to reduce pepper maggot infestations in pepper - with a ring of cherry peppers around bell peppers - and diamondback moth in cabbage - using collards as the trap crop. For more information visit the UConn website at http://www.hort.uconn.edu/ipm/veg/htms/trpcrops.htm
- Use a rotated field where cucumber beetle populations are not extremely high.
- Plant the trap crop earlier or at the same time as the main crop.
- Use the same in-row and between row spacing to plant the main crop and the perimeter trap crop row (or rows) of Blue Hubbard. Plant the outside rows along the length of the block by machine. Trap crop plants at the end of each row can be placed by hand or by machine (drive across the rows). Don't worry if all the Blue Hubbard plants don't line up with the main crop rows or are killed between rows by tractor tires. As long as most of the border plants survive on all sides of the field, without major gaps (>15 ft), the barrier should still function.
- Scout the trap crop at least twice weekly and spray the border with an effective insecticide (Pyganic) as soon as beetles are found. Don't wait for beetles to build up in the borders. It is important to maintain healthy border plants and to prevent redistribution throughout the field. However, even without border sprays, PTC reduces beetles in the main crop. Scout again to determine if repeat sprays are needed in the border.
- Don't mix another, highly attractive vine crop inside the border. Or, if you do, monitor it closely to determine if sprays are needed on that main crop. For example, zucchini is more attractive than summer squash and may need to be sprayed even if it is inside a blue hubbard perimeter.
- Where heavy infestations might be expected, such as borders along woods where beetles may have overwinter, use a wider perimeter of 2-3 rows.
- Watch for more details on twilight meetings at demonstration farms in Connecticut and Mass!
Adapted from PTC for Yellow and Green Summer Squash and Perimeter Trap Cropping Works!, by T Jude Boucher and Robert Durgy, University of Connecticut Cooperative Extension System.
ALERT - Potato Leafhopper
Watch fields for potato leafhopper. The leafhopper has been reported in Wells and in Dresden. You do not want to miss this pest because populations build up quickly and once significant feeding takes place plants will not recover and the whole crop could be lost.
Adults are about an eighth of an inch long, light yellow-green, and fly up from foliage when it is disturbed or shaken. They can best be monitored with sweep nets. Or, you can try to track one of the little flying critters and see them land. They have a characteristic wedge shape. Nymphs are found on the underside of leaves. They are smaller, light green, also wedge-shaped and very fast-moving. The nymphs run sideways and backwards as fast as forward and this is a real key that you have leafhoppers.
Damage can be severe on early-season varieties of potatoes, beans and strawberries. By the time you see the plant symptoms it is too late. That is why you must scout for the insects and control them if you have a significant population. The damage is called hopperburn because it usually starts as browning of the edges of the leaves. Later the whole leaf turns brown and dies. A whole planting will go down in a matter of days and is often confused with a disease problem.
Adults and nymphs feed by inserting a needle-like beak into the plant and sucking out sap. They also inject a toxin into the plant, which disrupts the food conducting tissue of the plant (ploem) and causes the yellowing, browning, and curling of leaves. In potato, leaf margins turn brown and brittle first, followed by death of entire leaves. In beans, the leaf turns mottled brown. Both adults and nymphs cause damage.
Some late-season varieties of potato such as Katahdin seem to have more tolerance.
Pyganic is the best material that organic growers have for this pest. Crop rotation will not help because the leafhopper is not overwintering here but rather flies in from way down south.
New Organic Bait Options For Slug And Snail Control
(By Becky Grube, UNH Vegetable and Sustainable Agriculture Specialist. Reprinted from the UNH Vegetable, Berry and Tree Fruit Newsletter)
Organic growers that experience major slug damage now have a new tool to help them prevent these losses. Recently, the Organic Materials Review Institute (OMRI) list-ed “Sluggo” and several other brands of iron phosphate slug and snail bait on their list of brand name materials approved for use by certified organic growers. As with other ‘restricted’ materials, it can only be used if other management practices are insufficient to prevent or control the slugs. Slug and snail damage can be particularly significant on many types of crops, particularly on young crops when soil moisture and relative humidity is high. Snails and slugs (which are shell-less snails) need high humidity and undisturbed soil to develop and reproduce. According to Alan Eaton, UN-HCE IPM Specialist, some of our common slugs are Europe-an and some are native. However, all of our common species spend most of their time underground or under debris, and come to the surface at night to feed.
There are many slug control options. Slug damage can be reduced by making an unhospitable habitat (dry and warm) by removing items which could serve as shelters (deep mulches, boards, rocks, etc.). Slugs can also be controlled by trapping. Shelters such as boards and rocks can be used to trap slugs, but in order to be effective, slugs must be regularly removed and destroyed. Fermented liquids (a mixture of yeast, sugar and water, or beer – see below) placed in submerged cups in the ground can also be used as traps in which slugs will drown. Slug baits are probably the most reliable and efficient meth-od of slug control. Commercially available baits or pellets contain molluscicides, poisons that kill snails and slugs. Two chemicals are licensed and formulated into slug and snail baits for use on home gardens and on food and seed crops in the United States - metaldehyde and iron phosphate. Of these, iron phosphate is far less toxic and has been shown to be just as effective as metaldehyde baits for slug control. Iron phosphate is considered by the U.S. Environmental Protection Agency to be GRAS (generally regarded as safe) for food use. No toxicity has been seen in mammals, birds, or fish. It is applied to soil as part of a pellet that also contains bait to attract snails and slugs. It is not volatile and does not readily dissolve in water, which minimizes its dispersal beyond where it is applied. This also means that it will remain effective after repeated rain events, unlike metaldehyde. Snails and slugs are more sensitive to the effects of iron phosphate than are other organisms. When the pests eat the pellets, the iron phosphate interferes with calcium metabolism in their gut, causing the snails and slugs to stop eating almost immediately. They die three to six days later. Iron phosphate slug and snail baits, originally used in Eu-rope, have been registered in the United States since 1997. These are sold as pelleted bait, typically applied to the ground around plants or crops. Several slug bait products contain-ing iron phosphate are registered in NH. When I checked the Division of Pesticide Control website, seven products were listed: Sluggo, Sluggo Plus, Bonide Slug Magic, Spectracide Snail and Slug Killer, Bayer Advanced Dual Action Snail and Slug Bait, Worry Free and Garden Safe Slug and Snail Bait. Two of these, Sluggo and Garden Safe Slug and Snail Bait, are also listed on the OMRI list of approved brand name products. In case of any question, it’s always a good idea to contact your certifier before you purchase a product. And as with any pesticide, always follow the label instructions! Lest you all think my newsletters tend to be a touch on the dry side, I’ll include, strictly for entertainment purposes, some relevant song lyrics that Alan Eaton sent me when I asked him to confirm some slug facts for me.
Now slugs is bugs that nobody loves but everybody understands
Cause they look disgusting, and they taste disgusting
And they feel disgusting in your hands
But of all the little bugs that grow in the garden
Slugs have a special place in my heart
And they never quit drinking once they start
So come on down, lets go out and have a slug drowning party tonight
No they can’t tell if they’re floating in Gui-ness or sinking in Miller Light
They ain’t particular and they go no taste
And they’ll drown in any beer in sight
So come on down, let’s go out, and have a slug drowning party tonight!
- From Dan MacArthur’s ‘Yucky Bugs’.
Information obtained from Ohio State University fact sheet HYG-2010-95, the U.S. Environmental Protection Agency, and the Organic Materials Review Institute (http://www.OMRI.org). Clipart courtesy the Florida Center for Instruc-tional Technology.
SQUASH BUGS IN VINE CROPS
(By --R Hazzard, UMass Extension Vegetable Program with information drawn from: T. Jude Boucher, Univ. of Connecticut and Beth Bishop, Michigan State.Reprinted and modified from the UMASS Newsletter)
Squash bugs have for many years been considered a minor pest in vine crops in New England. However in recent years some growers are find-ing higher numbers and resulting crop damage. It is important to assess wheth-er damaging numbers are present. Growers don’t need to try to get rid of every squash bug, but it is important to be aware of what risks exist. Adult squash bugs are 0.5 to 0.75 of an inch long, flat, gray-brown, and usually found on the underside of leaves, under residue, or in cracks in the soil. Squash bug eggs are laid in tiny clusters (usually on undersides of leaves in the notch between leaf veins) and change color from yellow to bronze shortly before hatching. Wingless nymphs are light gray with black legs and grow darker as they become adults in late summer. There is one generation per year. Adults spend the winter in crop residues and protected sites in or near the field. Photos of adults, nymphs and eggs are in the Pest Identification Supplement to the New England Vegetable Management Guide. The Supplement is avail-able in hard copy from UMaine Extension Offices or as a downloadable pdf file at the Guide website (http://www.nevegetable.org); photos are on the web individually at http://www.umassvegetable.org) Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Feeding causes wilting in leaves, stems, and vines that are beyond the feeding site. The injury may also appear as light-colored areas that later turn brown and die. These symptoms are similar to bacterial wilt symptoms. Later in the season, squash bugs may feed on the fruit. Squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense.
Crops affected. Pumpkin and squash are the cucurbits most affected by squash bugs, because they prefer to lay eggs on these crops and because the nymphs flourish. Because of low attrac-tion and low survival rate, squash bugs do not usually become a pest on cucumber, watermelon, butternut squash and muskmelon. Cucurbita moschata crops such as Waltham butternut have been found to have fewer squash bugs. If summer squash gets away from you and gets too big to harvest, squash bugs will move in and feed on the unharvested fruit.
Cultural practices influence squash bug numbers. Clean culti-vation lowers the attraction of crops to squash bug. We have ob-served higher numbers in fields with hay or straw mulch and in low-till or no-till situa-tions where cover crop residues are high. Blue Hubbard squash as a perimeter trap crop has shown some efficacy in trapping squash bugs as well as cucumber beetles, because it is preferred over many other vine crops. In Texas, many growers have successfully used early-planted straightneck summer squash (‘Lemon Drop’or ‘Hyrific’) as a trap crop in the border rows of their watermelon fields to attract and control squash bugs to man-age CYVD.
Scouting and threshold. The key to preventing squash bug problems is early detection and control of small nymphs. Scout for squash bugs adults and eggs by searching upper and lower leaf surfaces and soil cracks around the plant. Insecticides may be warranted if squash bugs are causing wilting of young plants (if wilting is observed and squash bugs are present on the underside of leaves). Just before flowering, fields should be scouted for egg masses. This is the critical time to control squash bugs. If more than one egg mass per plant is found, an insecticide application is needed. Adult squash bugs and older nymphs are more difficult to control because they develop a hard exoskeleton as they mature. In addition, since squash bugs are secretive and the canopy grows thick, they can be difficult to reach with insecticides. The only OMRI listed (organic) products that have been shown to offer any control are azadirachtin (Neemix 4.5) and Pyganic, both for application to young squash nymphs. Large nymphs and adults are not really effected by any organic approved materials. That is why it is so important to do as much culturally as possible and scout NOW for early control. There is also a parasite of squash bug that may be visible in the field. It is a tachinid fly, Trichopoda pennipes, which has a colorful bright orange abdomen and dark wings. Eggs are laid on the abdomen of the adult squash bug; parasitism may be as high as 80%, but unfortunately, the adult squash bugs are not killed before they feed and lay eggs on plants. Squash bugs may also vector a relatively uncommon but serious disease, Cucurbit Yellow Vine Disease caused by the bac-terium Serratia marcescens. The presence of this disease was first noted in New England in 2003. If this disease has occurred on your farm, it is critical to focus on controlling early season adults to prevent its spread. A good article by Jude Boucher on cucurbit yellow vine may be found on the web at http://www.hort.uconn.edu/ipm/veg/htms/cucrbinct.htm
WARM SOIL IS HERE
Now that the soil has warmed up I think many of the problems of May and early June are a thing of the past (see the previous Pest Report piece on cold soil problems). I am still getting calls about problems from a week or two ago such as; seed corn maggot (beans germinated without leaves), and wirestem (spinach and broccoli germinated but then never grew and eventually the stem just above the soil withered, shrunk and the plants wilted), and chilling injury in cucurbits (melons, cucumbers and squash wilting), which is probably due to them being planted in soil that was too cool or the air was too cool (here in Greene we were in the 40s many nights of the first half of June). The cucurbits may grow out of this and may not, depending on how damaged the roots are. By the way, the plants are wilting because the roots just do not function in cool soil and, if cold, much of the root may have died. Well, the soil is warm now and for some crops there is still time to try again.
FLEA BEETLES IN BRASSICAS
(modified from an article in University of Massachusetts Extension Vegetable Notes)
Flea beetles are busy feeding in spring plantings of Brassica crops. On farms where Brassica crops are grown season-long in succession plantings, this insect has changed from a minor to a major and very destructive
pest. Some growers depend on row covers for managing it in early crops, while others depend on sprays. Crop rotation is an effective strategy and it is not too late to incorporate rotations into your planting scheme for
the rest of the season.
Crucifer and striped flea beetles feed on all Brassica crops as well as weeds that are in the same family, such as yellow rocket or wild mustard. The crucifer flea beetle is uniformly black and shiny, longer than it is wide, about 2 mm in length, while the striped flea beetle has two yellow stripes on its back. Potato flea beetle (found on eggplant, tomato and potato) is also black, but is covered with fine hairs and somewhat more blocky in shape. Knowing these a different species that feed on brassicas or plants in the potato family can help plan rotations.
Flea beetle adults feed on leaves and stems, resulting in numerous small holes, or shot-holes. Eggs are laid in the soil starting in mid May, and beetle larvae feed on roots. The non-waxy or glossy greens (arugula, bok choi, tatsoi, mustard, Chinese cabbage, komatsuna) are preferred to the waxy cabbage, kale and collard types of brassicas. In brassica greens, beetles feed on the whole surface of the leaf, and will continue feeding from the seedling stage until harvest. Waxy crops are most susceptible at the cotyledon and seedling stage and feeding is more limited to leaf margins. However, high populations of flea beetles can cause severe injury, stunting, or plant death even in the waxy types of Brassicas.
Crop rotation is a key strategy for keeping numbers down. To reduce and delay flea beetle invasion of spring crops, move them as far away as possible from the fields that were used for fall Brassica crops. Fields that are isolated by distance (the farther the better) and by roads, woodlands, houses, or fields with other crops will have lower numbers and be colonized later. Beetles overwinter in field borders near last year's crop. Planting close by ensures a high population in the spring.
Crop rotation also works to reduce damage to fall brassica crops. The second flush of adults, emerging from underground where they fed on roots and formed pupae, begins sometime in late July. These adults are heavy feeders. Fall crops planted close to spring crops will be heavily damaged, but those planted in a field that is isolated from spring crops will have much lower populations and less damage.
Occasionally in tender greens such as arugula, tarnished plant bug feeding may be confused with flea beetle feeding. In addition to the shot holes from flea beetles, there may also distorted leaves that are typical of TPB feeding, which injures leaf tissue when leaves first emerge.
One of the most effective ways to protect Brassica crops from flea beetles is to place a floating row cover over the bed or row. It is critical to seal the edges immediately after seeding, because Brassica seeds germinate quickly and beetles rapidly find the cotyledons. Flea beetles can fit through extremely tiny cracks. Edges of the cover must be sealed on all sides using soil, black plastic bags filled with soil, or some other method.
Lighter weight covers should be used when the summer heat arrives; heavy covers can reduce yield.
Thresholds for treatment will vary with Brassica species and the quality demanded by your market. The threshold for greens is obviously much lower than for cabbage. One study in Colorado found that an average of 5 or more flea beetles on seedling broccoli reduced subsequent head size. Cornell and Rutgers Universities recommend a threshold of one flea beetle per plant on seedlings up to the 5 leaf stage, or injury and 1 beetle/plant on 50% of the stand. It is most important to scout your own crop and assess the numbers of beetles, amount of damage, crop stage, and market needs.
For organic growers, spinosad (Entrust) is effective in suppressing flea beetles and reducing damage.
Pyrethrin (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. I suggest that if you use Pyganic that you spray for flea beetles either in the evening or very early in the morning (before 5 am).
Last year, as part of a three-state SARE Partner Grant, we tested a Perimeter Trap Crop (PTC) system for controlling flea beetles. We used more attractive greens (Brassica rapa types) as a trap crop for cabbage, collard, kale or broccoli (Brassica oleracea). Komatsuna was our choice for the perimeter trap because it is highly preferred compared to cabbage, seed is inexpensive, growth is rapid, and the crop continues to produce new, attractive foliage over a long period. However, other long-lived B. rapa types including Chinesse Cabbage could be possible. Borders were sprayed with spinosad. If growers are interested in trying this in later-season plantings, please call Pam Westgate or Ruth Hazzard at (413) 545-3696.
CATERPILLARS IN BRASSICA CROPS
(modified from an article in University of Massachusetts Extension Vegetable Notes)
Imported cabbageworm is active in Brassica crops now in Massachusetts and I have seen the moths flying here in Maine. In Mass. they are finding a range of caterpillar sizes on cabbage, collards, kale, and broccoli and other cole
crops. Diamondback moth has also been observed, though numbers appear to be low. Diamondback moth and imported cabbageworm have several reproductive cycles each year, and this is probably the first generation. There has been no sign of the third major caterpillar pests of Brassica crops, the cabbage looper, which usually does not appear until mid July or August when it migrates into the region.
If you are scouting for cabbageworm, you may also find a very interesting drama taking place! A parasitic wasp that was released in 1990 in Massachusetts is gaining ground and producing high levels of parasitism in imported cabbageworms seventeen years ago. Dr. Roy Van Driesche of the UMass Dept of Plant, Soil, and Insect Science introduced Cotesia rubecula, a small wasp that lays its eggs in small imported cabbageworms (first and second instars). One immature wasp grows inside each caterpillar, then crawls out and spins a small white cocoon. Soon another adult wasp emerges from the cocoon and seeks out more caterpillars. When you scout your fields, if you
see caterpillars that look somewhat lighter green (especially in the mid section) and somewhat sickly, they may be destined for an early death, because a parasite is growing inside. Some growers have also observed what looks like a strange, pale predator feeding on the cabbageworm: this is probably the immature wasp crawling out, ready to make a cocoon. Dr. Van Driesche has been conducting a survey of cole crop fields in the Connecticut Valley. Eighty percent or more of the cabbageworms that he has found are parasitized. This is good news for cole crop growers, who have a helping hand in combating this pest. This is a good reason to use selective products if you do need to spray for caterpillars.
Quick ID Cues:
Diamondback moth caterpillar: very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons, with a green full-grown caterpillar or a brown pupa inside.
Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow.
Cabbage looper: light green, smooth, loops¹ up like an inchworm as it moves, grows 1 1/2 to 2 inches. Eats big holes in leaves.
Cross-striped cabbageworm: Gray with black tubercles, as it grows becomes bluish-gray with numerous transverse black bands. There is a yellow line along each side of the caterpillar.
Scout undersides of leaves to look for fresh damage and notice caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.
For organic growers both Bt and Spinosad are very effective, but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying.
THREE LINED POTATO BEETLE
The Three Lined Potato Beetle is also referred to as the Old Fashioned Potato beetle. I often get calls from people claiming that cucumber beetles are feeding on their potatoes or other tomato family crops, especially tomatillo. It only slightly looks like a cucumber beetle. The Threelined Potato Beetle (Lema trilineata) adults are reddish-yellow with three broad black stripes on their backs. Larvae have granular masses of excrement all over their bodies. Both larvae and adults feed on the foliage.
This critter does much less damage to potatoes than the Colorado Potato Beetle. But it is hammering hard right now on tomatillo.
Hornworms are probably the most destructive insect that attack tomatoes and I have already had a report of them. Later in the season they are likely to be out in force both in hoophouse and field tomatoes. It seems they are wintering over here now because when I first moved to Maine 20 some years ago they were a rare problem and now I see them every year.
They are giant caterpillars that can do a vast amount of eating in a very short time. Sometimes it seems that overnight healthy looking tomato plants are striped of their leaves leaving bare stems. The hornworms will also
attack the fruit eating gouges out that look more like bites of a furry animal than an insect. Look now for the damage and the frass which is black pellets laying all around plants hosting hornworms.
The adults are large, fast flying hawk moths, which in flight may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.
Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem is that they blend in very well and it is easy to overlook one or two caterpillars that can do significant damage in a day or two.
Bt works very well on this caterpillar, especially when they are small.
What Are Those White Things On Tomato Hornworms?: Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs on laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworms body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize. (bits of this were reprinted from 2005 Vermont Veg and Berry News by Vern Grubinger)
EARLY CUCURBIT TRANSPLANT LOSSES
(Modified from a piece in the Umass Extension Vegetable Notes by Andy Cavanagh)
Massachusetts is a week or two ahead of Maine and it is not surprising that we are going to experience the same thing they did a few weeks ago. It is time by the calendar to get the cucurbits out into the field and yet even
though there was some warm weather earlier, it is now wet again and going to get cold in a day or two. This variable weather wreaked havoc with many growers in Massachusetts for their early cucurbit transplants and may do the same here. The warm weather pushed cucumber and squash seedlings along quickly and some folks have moved them out of the greenhouse, or really want to get them out and put them into the ground soon. But be careful because cool weather and wet soil may cause transplants to collapse. The cold soil, combined with the somewhat leggy, tender transplants and wet weather not only leaves the small amount of roots struggling to provide the top of the plant with what it needs, but also creates an opening for whatever pathogens that are naturally present in the soil to get a foothold. In Massachusetts they saw root rots and wilts caused by a number of different pathogens (including Pythium, Phytophthora, and Rhizoctonia), some of which thrive under cool and wet conditions. They also observed some leaf scorching that may have been a direct result of the cold weather. The cucurbits suffer from what is called chilling injury without even having to be frosted. If the roots sit in cold wet soil and the air warms you may also see the plants wilt. This is the result of the roots not working and the top of the plant transpiring normally. My advice (seeing eye to eye with Becky Grube - Vegetable Specialist at UNH where the advice originated) is to follow your soil thermometer and not rely too much on the calendar. I suggest you do not put cucurbit transplants into soil less than 60 o F.
There are two types of asparagus beetles, the common and the spotted. Adults of both species and larvae of the common feed on the fern of asparagus and reduce the vigor of the bed over years. Larvae of the spotted feed almost entirely inside the berries and effect seed production but do not hurt the plants. Both species overwinter in crop residue and become active in the spring. They feed on the ferns and lay eggs that hatch in about two weeks. Then the larvae of the common feed for three to four more weeks and really weaken the plant if they are numerous. Then they drop to the ground and pupate at the soil level or just below. New adults emerge in later July and by September are looking for overwintering sites.
This time of year you can greatly reduce the population by harvesting ALL of the spears. The beetles are becoming active now and leaving some spears to develop into fronds give them feeding sites. If you harvest ALL of the spears right to the ground during the harvest period you will starve many of the beetles and fewer will make it to the time you stop harvesting and let the fronds grow. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter. As a last resort in a really bad infestation, Entrust works well.
MANAGING COLORADO POTATO BEETLE
-(modified from an article in UMASS Vegetable Notes a few years ago by Ruth Hazzard. R Hazzard says thanks to sources including: D Ferro (Umass Amherst), J. Mishanec (CornellUniversity), Jude Boucher (Univ. of Connecticut).
Colorado potato beetles (CPB) are will be moving into potato and eggplant crops soon, and will shortly be laying eggs. Some adult beetles spent the winter in last year’s potato fields, but most moved into the woods and brushy borders next to these fields, where they burrowed into the soil up to a depth of 12 inches. In spring the beetles have to regrow their flight muscles before they are able to fly. At first they search for food plants by walking from the field edges. This is why the edge of non-rotated crops are attacked first. If beetles do not find host plants via walking they will fly some distance in search of food. Once host plants are found adults begin to feed and lay eggs. The beetles will have mated the previous fall or late summer; hence they have no need to mate in the spring to produce viable eggs. However, they do continue to mate in spring. The bright yellow eggs are laid in clumps that average 30-35 eggs, generally on the undersides of leaves.
Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from the previous year’s fields. Barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season. Also, the total population of
adult beetles is lower, producing fewer larvae to control. Now is the time to scout for adults, eggs and egg hatch.
Walk your fields and look for CPB adults and eggs. The economic threshold for adult beetles in potato is 1 beetle per 2 plants (or per 2 stalks, in midseason). Eggplant seedlings have a low tolerance to damage. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch. Larvae go through four stages before they drop to the soil and pupate. In the first stage, the larvae are about the same size as the eggs and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It’s a good idea to prevent beetles from ever reaching the fourth instar! After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. Ten days later the next generation of adults emerge and feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites.
Spray timing and thresholds.
To prevent resistance the best strategy is to alternate among classes of insecticides in each generation, and throughout the season. An example would be to use a material such as Spinosad (Entrust), which controls adults and larvae for the first spray, followed by a Bt (Novodor) to kill emerging young larvae. BUT, at this time there is no Bt formulation approved for use in organic systems. NOVODOR IS NOT APPROVED FOR ORGANIC PRODUCTION BECAUSE OF INERT INGREDIENTS. VALENT, THE COMPANY THAT MANUFACTURES IT, AT ONE TIME SAID THEY WOULD REFORMULATE IT TO MEET ORGANIC STANDARDS, BUT SEEM TO HAVE CHANGED THEIR MIND. GIVE THEM A CALL AND TELL THEM HOW IMPORTANT IT IS TO ORGANIC GROWERS (1 800 323 9597).
If you are not organic and are using Bt (Novodor), you want to make the first application when 20- 30% of the eggs have hatched. If you are using spinosad (Entrust is the organic formulation) you can wait until more larvae have hatched, when the oldest larvae reach the third instar, when they are about 1/3 inch long. Applications made at this time with Entrust will kill all the larvae that have hatched up to this point. The threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason), based on a count of 50 plants or stalks. Thresholds established in the Northeast for eggplants from seedling to fruiting stage include: 15 CPB per 10 plants (Rutgers) or 2 small/1 large larvae per plant (<6 inches) or 4 small larvae /2 large per plant (>6 inches) (Cornell). In eggplant, in addition to defoliation, beetles sometimes clip the stems of flowers or flower buds. This directly reduces fruit formation and marketable yield. On the other hand, potatoes can tolerate 20% defoliation without reduction in yield (or even more, later in the season and depending on cultivar. Allowing these later populations to exist without spraying will delay development of resistance to the insecticides).
Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop between overwintering sites and this year’s crop and get it in earlier than the main crop; then control early-arriving beetles with a foliar insecticide. In eggplant or tomato, the perimeter border can be an Italian eggplant type, which is more attractive to both CPB and flea beetles. Treat only the border, as soon as beetles arrive.
Another strategy for beating the beetle is to plant late. CPB adults that do not find food leave the field in search of greener pastures. Planting after mid-June, using a short season variety, often avoids CPB damage and eliminates the need for controls. Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.
Strawberry (adapted from Dave Handley's Umaine Small Fruit Newsletter)
Strawberry Rootworm - Strawberry rootworm adults and feeding injury has been found on strawberry
leaves in fields this week. The adult stage of this insect is a small (1/8”) dark brown beetle. The beetles feed on strawberry leaves during the spring and late summer, causing numerous small holes in the leaves. The adults in fields now will soon lay eggs. The larvae are small grubs that feed on the roots of strawberry plants, causing them to be stunted and weak. There is no organic spray that helps significantly, so this is another pest that demonstrates the importance of rotation to organic strawberry growers.
Root Weevil - From info supplied by Richard Cowles, CT Agricultural Experiment. Station; Peter Shearer, Rutgers Cooperative Extension; and others We have observed some plantings of strawberries infested with the grubs of black vine weevil and strawberry root weevil this spring. Infested plants appear week and stunted, usually in somewhat circular patches in a field. Digging under the plants will reveal small (1/4 -1/2”) crescent-shaped legless grubs. It is not too late to put on an application of nematodes to control the grubs (optimal timing is about mid-May). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees (‘J-3
Max Hb’ from The Green Spot; ‘GrubStake HB’ from Integrated Biocontrol Systems; ‘Larvanem’ from Koppert Biologicals). Beneficial nematodes can also be applied in late summer (August 15 - September 1), and in that case,
Steinernema feltiae (‘Nemasys’ from Griffin Greenhouse Supply, ‘Gnat Not’ from Integrated Biological Control Systems, ‘Entonem’ from Koppert Biological) should be considered in northern locations since it tolerates cooler soil temperatures and completes its life cycle quickly. Once the grubs begin to pupate (usually early June) nematodes should not be applied, because they do not attack the adult (beetle) stage. Neem-based products containing azadiractin (such as Aza-Direct) may be acceptable for organic production, and while neem will not kill the adults it can disrupt egg-laying if applied at high rates at least twice.
Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive, refrigerating if delay is necessary. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another 1⁄4 inch of irrigation after application to wash them onto and into the soil. Although references suggest rates of several billion nematodes per acre, I found researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of about $100 to 200 acre depending on volume and source. Ironically, nematodes probably work best in the worst weevil-infested fields. High populations of weevil larvae allow explosive growth in nematode populations, while low populations of larvae may not permit efficient nematode reproduction. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven’t taken over the roots.
Root weevils cannot fly, so they infest new plantings by wandering into fields from surrounding weedy and woodland vegetation, or in large numbers from recently plowed, infested strawberry plantings. Even plantings several hundred feet away can become generally infested as a result of mass migration from plowed fields. A good rotation program with substantial distance between strawberry fields can help to manage root weevils. Also, when turning under old, infested strawberry plantings, it is critical to leave a row or two at the perimeter of the field as a trap crop to protect
other plantings. Adult weevils will be intercepted in these rows before they leave the field and thus lay their eggs where the larvae will not do any damage. At the end of the season the trap rows should be turned under prior to planting winter rye. Do not spray the trap rows as this may repel weevils and result in more migration to other fields.
Some Beneficial Nematode Suppliers:
The Green Spot: 603-942-8925 or www.shopgreenmethods.com
Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com
Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com
Koppert Biologicals: 800-928-8827 or www.koppert.com
CABBAGE MAGGOT FLIES
(adapted from UMass Extension Newsletter)
A good indicator of the start of cabbage root maggot flight is blooming of the common weed yellow rocket. Cabbage maggot flies are likely to be found only near their host crop, brassicas. Flies spend the winter as small brown pupae in the soil. Adults emerge in spring and can then travel up to a mile in search of host plants. About 6 to 10 days after the flight of adult flies eggs are laid. Female flies seek out brassica plants to lay eggs at the base of the stem. Cool, moist soil conditions favor survival of the eggs. By late June, if the soil temperatures in the upper ∏ to 1 inch are above 100 degrees F then the heat of the soil itself provides control.
When eggs hatch, larvae feed on roots and can cause complete destruction of the root system. In brassica root crops such as turnips, radishes and daikon, feeding tunnels make the root unmarketable. In crops such as broccoli or cauliflower the first sign of a problem is wilting of the plant on sunny days and yellowing of outer leaves. Later, plants collapse, wilt down, and die. If you pull one up you will see that the roots are gone. You may still find the little white maggots feeding, or the small brown, oblong pupae.
Monitoring for adults. Cabbage root maggot flies are rather delicate, hump-backed gray-brown flies, about 5-7 mm long. The flies are attracted to yellow sticky cards, which are inexpensive and easy to use. Attach them with small wire stakes and place near the soil. It‚s best to check traps twice weekly, as they often get coated with dust when left out for a whole week. This will tell you when the flight peaks, and when it declines. In cabbage, flight typically declines after mid-May so that some late May or June plantings do not get attacked (Maine is a week or two later). You can time your transplanting to try and avoid peak flights, and thus damage.
Monitoring for eggs. To check your field for eggs, look for the 1/8-inch long, torpedo-shaped white eggs that are laid along the stem, or on the soil next to the stem of young transplants. Often eggs are laid in neat rows, or inserted into the soil. They may be under a small clod of dirt near the stem. Eggs may be more abundant in wetter areas of the field. A pencil point helps stir the soil to look for them. Check 25 or more plants, in groups of 2 to 5 plants, scattered around the field. If you have several plantings, scout each planting (it takes about 15 minutes).
Organic growers do not have effective insecticide options for this pest so cultural practices are critical.
Floating row covers provide an effective barrier against this pest. Use in a rotated field, as flies overwinter in soil after late season crucifers and could emerge under the cover if the same field has spring brassicas. Replace cover after weeding operations. Crop rotation contributes to keeping populations low. Fall tillage to bury crop residues and to expose over-wintering pupae is also important. If the pest is present in a healthy crop, cultivation that brings soil up around the stem may help encourage formation of adventitious roots from the stem, which can help compensate for root loss due to maggots. Natural enemies in the soil may also help to suppress the population of maggot eggs and larvae.
The onion maggot is in the same genus as the cabbage maggot and has very similar habits. I have received calls this year about it and I lost an entire crop a few years ago. It is one of the most serious pests of onions. Onion is the preferred host and related crops such as scallions, garlic, leeks and shallots are only occasionally infested. Wild onion is not an important host either.
The greatest damage is caused by the first-generation larvae that attacks young seedlings in the early spring. They move up rows to new plants as they devour the young seedlings quite quickly and need more food. The first symptom seen in very young seedlings is a slight wilting of the plant. Later they will simply disappear. Plants attacked at later seedling stages will turn a grayish yellow and wilt and will later detach at the ground level as the maggot consumes everything below ground. Onion plants attacked later are rarely killed and fewer plants are attacked as the maggot does not move to new bulbs. However, plants attacked at the later stage are likely to have misshapen bulbs and usually are later attacked by fungi and rot.
The onion maggot overwinters as a pupa in the top five or so inches of soil. When spring soil temperature rises above about 40 degrees the overwintering pupae begin to develop and, depending on the weather, in a number of weeks the adult onion maggot flies will emerge and fly around and mate. Later they will search for onions to lay eggs around. Eggs are laid around the base of onion plants and the resulting larvae crawl down to start feeding on
the roots. There can be three generations in a season.
Adults of later generations disperse very little from onion fields so crop rotation is a very important tool for avoiding infestations. Good sanitation is very important because cull onions will attract flies that will lay eggs that result in overwintering pupa. Damaged onions are the preferred site for egg laying so avoid mechanical damage to onions and dispose of any damaged onions rather than leaving them laying around the field. Discing onion fields in the early fall when the flies are still active actually makes things worse because it makes many pieces of onions and so increases the number of sites for egg laying. Ash and diatomaceous earth around the base of onion seedlings may deter egg laying and maggot survival.
COLD SOIL TEMERATURE AND SEED GERMINATION
I have received a number of calls about very poor seed germination both in the greenhouse and in the field. In my mind this is due to low soil temperature. This spring has been challenging with days on end of very cloudy, damp, cold weather and this effects greenhouses too since they do not warm during the day and we are all guilty of trying to save heating fuel at night.
Seeds of many crops are adapted to germinate in warm soil (corn, melons, etc) and will take dramatically longer to germinate in soil even only slightly cooler than their optimum temperature for germination. Here is a table of just a few examples of how temperature effects seed germination:
CROP OPTIMUM RANGE DAYS REQUIRED @ DEGREE F
590 F 770 F
Melon 75-95 does not germinate 4
Pepper 65-95 25
When a seed sits damp and cool for a long time it becomes very susceptible to some diseases and insects. And those of us using compost based soil mixes may have the organisms that cause problems waiting right there in the mix. As you can see above, greenhouse temperatures that we had a few weeks ago in that rainy stretch resulted in seeds just sitting….like sitting ducks for disease attack. Here are two problems that I think had a field day in crops this year and may still be a big problem if folks get fooled by this hot day today and rush to plant some things that do much better in warm soil:
PYTHIUM ROOT ROT
Pythium is one of the most common fungi found in roots of greenhouse crops and is usually present in field soil. It is a natural inhabitant of the soil and can survive there indefinitely as well as in debris in the greenhouse. Stunted growth and wilted plants are common above-ground symptoms caused by Pythium root rot. To examine plants, remove plants from pots and examine roots. Healthy roots are white and firm; decayed roots may be dark colored
and the rotted outer covering of the root slips from the central core.
Growers having re-occurring problems with Pythium, should review their overall production practices including fertilizing, watering and media handling in greenhouses, and may want to scale back on their rush to plant seeds outdoors. Over-watering and excessive fertilizer levels promote Pythium. Allowing the soil surface in containers to dry before watering again helps. Good sanitation is crucial for prevention in greenhouses. Keep hose ends off the floor, wash hands before handling plants and avoid contaminating growing medium.
Since symptoms can be confused with other causes such as high soluble salts or other diseases, suspicious plants should be diagnosed through your University diagnostic lab. -(Adapted from article by Tina Smith, UMass
Peas, beans, corn, potato sprouts and even some seeds in the greenhouse are attacked by the larvae of this fly. They are yellow-white maggots about a quarter of an inch long and sharply pointed at the head end. The symptom is
usually that you see no germination, and when you dig around you may find nothing left or may find the maggots burrowing into the seed. Sometimes the seed germinates but only a weak or partially eaten plant is seen. The
injury is most likely to occur in cold wet seasons where the germination is slow, and also in soil high in organic matter.
The attack is early in the spring because the critter spends the winter as pupae in the soil or maybe free maggots in manure or unfinished compost. The adult is a grayish brown fly only about a third of an inch long. It emerges in early spring and deposits eggs in rich soil, compost piles or near seeds and seedlings. Exposed peat or potting soil mix of transplants can also serve as attractive sites for females looking for a place to lay eggs. There are a few generations each season.
The best method of dealing with this critter is to do everything you can to encourage quick germination and rapid growth. In the cold, wet soils we have in spring the seeds are just sitting ducks. Shallow planting helps when conditions are poor. Best yet, wait for things to warm up and dry out.
NOTE: This is the first Pest Report for the growing season of 2007. I am sending it to the list I used last year. If you are a MOFGA certified grower, then you will automatically receive the rest of them this season. If you are not a certified grower and want to receive future reports, then please email me and let me know. The next report will be sent to the 2007 MOFGA Certified Grower list, and those others who make the request.
I want to remind you all and again thank my sources for much of the information in these reports. Extension educators from across New England are kind enough to allow me to use their material that they post in various places. Whenever I use a piece from someone else, I always cite the source and you may want to contact them after reading something and request to get on their direct mailing list. I modify the reports from Extension and tailor them to fit organic farmer needs.
POTATO PLANTING TIME: DON'T PLANT A PROBLEM
Potato seed tubers are often the source of infection for a crop and inspection before planting is well worth the time. Some problem seed pieces are not going to spread a disease and can be planted. Here are some common issues:
Ring Rot - This is one of the worst diseases you can get on your farm because once you get it, it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.
Scab - Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce. They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.
Black Scurf - If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, and then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.
Hollow Heart - Just as the name implies, the center of the potato is hollow. It appears as splitting within the tuber and the inner walls may be white, tan or even may be rarely infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.
Knobby potatoes - Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.
REDUCING HUMIDITY IN THE GREENHOUSE
(adapted from UMass Extension)
A key to suppressing foliar disease in the greenhouse is to keep the plant canopy dry, especially from dusk to dawn. This is accomplished through proper watering and adequate plant spacing, having well-drained floors, warming plants, moving air and venting moisture. The least expensive method is to keep the greenhouse dry, especially going into the night, when the temperature drops. Puddles on the floor and water on leaf and media surfaces evaporate and add moisture to the greenhouse, which creates humidity, and that takes away energy that is intended to keep a house warm. Water your plants just enough to prevent excess water on the floor, and water early enough in the day so plant surfaces can dry before evening. The highest relative humidity in a greenhouse is in the plant canopies, where moisture from transpiration gets trapped due to insufficient air movement. Adequate plant spacing and mesh benches will help to improve air circulation at the plant level. Remove weeds as they also contribute to high humidity.
Bottom heat will improve air circulation inside plant canopies and helps prevent condensation on leaf surfaces. As warm air rises it creates air movement around the plants, and it keeps plant surfaces warm, preventing condensation on them. Combining heating with ventilation is important for reducing humidity. Ventilation exchanges moist greenhouse air with drier outside air. Heating brings the outside air up to optimum growing temperature, and it increases the capacity of the air to carry moisture, avoiding condensation. Neither practice alone is as efficient as both combined.
To vent humid air in greenhouses with vents, the heat should be turned on and the vents cracked open an inch or so. When doing this the warmed air will hold more moisture (RH), escape from the greenhouse through the vents, and be replaced with outside air of lower RH. This natural rising of the air will result in a greenhouse of lower relative humidity. In houses with fans, they should be activated and operated for a few minutes and than the heater turned on to bring the air temperature up. The fans should then be shut off. A clock could be set to activate the fans. A relay may be needed to lock out the furnace or boiler until the fans shut off so that both the fans and heating system do not operate at the same time and flue gases are not drawn into the greenhouse.
The venting and heating cycle should be done two or three times per hour during the evening after the sun goes down and early in the morning at sunrise. The time it takes to exchange one volume of air depends on whether or not fans are used and the size of the fans and vents. For some greenhouses it may take only 2 to 3 minutes for air exchange. If using natural ventilation, it may take 30 minutes or longer. Heating and venting can be effective even if it is cool and raining outside. Air at 50 degrees F and 100% RH (raining) contains only half as much moisture as the greenhouse air at 70 degrees F and 95% RH. (Reprinted from Vermont Vegetable and Berry News, compiled by Vern Grubinger)
This is the time of year to start thinking about cutworms, which often become a real challenge especially for transplants and carrots and onions. Cutworms are the caterpillars of a few different species of night flying moths. Some of the species fly in very early in the spring and others in the fall. They lay eggs at the base of plants (weeds and cover crops in the fall). The eggs hatch into tiny, dark gray, greasy caterpillars that feed at night. Some species just simply cut off your plants just about at ground level. Other species climb up and cut off leaves. The caterpillars can be found in the soil by digging around. They curl up into a "c" shape when you handle them.
The big problem is you never know whether it will be a problem or not. On a small scale, Dixie cups with the bottoms cut out placed around a transplant make a good barrier.
One method that works on a large scale but is usually not practical is to starve them out. If you can keep a field completely free of any growing plants (weeds or crops) for a few weeks after they hatch then they will die.
I have received good reports about making bait from bran, a Bt solution and molasses and then sprinkling it or making patties and putting the patties along the row of effected crops.
I have also heard very good reports from folks who have used parasitic nematodes. The best results for cutworms is achieved when a combination of two types of nematodes are applied in a mixture because the different species work different levels in the soil and attack the cutworms both while they hide deeper in the soil during the day and when they move up at night. A mixture of Heterorhabditis bacteriophorea (Hb) and Steinernema carpocapsae (Sc) has essentially eliminated cutworm problems for some of our growers. The nematodes are usually shipped on a sponge ready to mix with water and apply to the soil. It is important not to let the soil surface dry out shortly after application. A few suppliers of these insect-attacking nematodes are The Green Spot (www.greenmethods.com), IPM Laboratories (www.ipmlabs.com), and ARBICO (www.arbico.com).