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 MOFGA's 2007 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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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 Œshot-holes. Eggs are laid in the soil starting in mid May, and beetle larvae feed on roots. The non-waxy or Œglossy 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 susceptible 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 damage to fall brassica crops. The second flush of adults, emerging from underground 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 addition 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 cotyledons. 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 covers 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 Colorado 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 important 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 suppressing 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 oleracea). 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 caterpillars. When you scout your fields, if you
see caterpillars that look somewhat lighter green (especially in the mid section) and somewhat 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 cabbageworm: 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 products 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 caterpillar or a brown pupa inside.

Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. 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, Œloops¹ up like an inchworm 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.


TOMATO HORNWORMS

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 hornworm’s 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)

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