Pest Report for July 17, 1999
Remember to thank all my sources for info if you run into them including Dave Handley and Jim Dwyer from U Maine Extension, Ruth Hazzard and Sonia Schoelmann from U Mass Extension, Vern Grubinger from Vermont Extension, Clay Kirby from the Pest Management Office and the MOFGA certified growers who take the time to send me reports from the field. Please send along anything interesting you note in your fields.
It is one beautiful day after another so if you are on vacation or have irrigation you are doing well. For the rest it is very dry and crop growth is slow. Those who have gotten water to the crops are having a great year. Jim Dwyer from the county reports that the rain and shower activity last weekend has continued to provide excellent growing conditions. With many fields filling the rows and in full blossom, the crop is shaping up to be one of the best in recent years.
Insect and disease problems are relatively light all over New England. However a few new reports are coming in and some of the critters from earlier are keeping up their activity.
TIPBURN AN BLOSSOM END ROT
These are physiological diseases, i.e., not caused by an organism but by environmental conditions. The dry weather has brought on a problem of calcium mobility in plants. Even in soil with plenty of calcium, plants may be having problems because they can not move it around when under water stress. The calcium does not make it to the growing points of the plant. This sometimes shows up as the above diseases.
I have received reports from a farm with tipburn in Chinese cabbage and seen it in my own regular cabbage. It also occurs in lettuce. The tips of the newer leaves turn brown and then desiccate to a thin papery consistency. It is a problem in the inner leaves of the head of cabbage. The affected area may range from a narrow zone along leaf margins or up to one-half of the leaf. Tipburn occurs as plants approach maturity; symptoms occur at one time and are not progressive.
There have been lots of reports of blossom end rot in tomatoes and summer squash The blossom end of the fruit turns brown and then rots.
There is a lot of varietal variation to susceptibility to these diseases. Practical means to avoid the problem include reducing nitrogen rates, maintenance of uniform soil moisture levels with irrigation, close spacing, and harvesting as soon as heads are mature.
BOTRYTIS (GRAY MOLD)
Botrytis has shown up in greenhouses. This is a disease that is brought on by environmental conditions. The spores for it are all over and cannot be avoided. It pops up as a problem when the plant tissue stays wet for too long. It is very common in strawberries and raspberries, but not this year because the weather is so dry. But, in greenhouses that are not ventilated well it can spread very fast through a tomato crop effecting the leaves, aborting blossoms and later rotting fruit. Keep as much air moving around your greenhouse as possible.
Closed greenhouses can also get too hot. Remember, pepper, eggplant, tomato, etc. do not pollinate well when the temperature gets above 85 or so. If you have lush growth and no fruit think about the temperature.
No fruit can also be the result of TARNISHED PLANT BUG. This critter is all over the state in big numbers. It is tan to brown with black markings on its back. They fly quickly about when you brush your crop with you hand. This year they are very heavy in potatoes killing the blossoms, which of course is not a big concern, but also killing the growing tips. If you see a lot of wilted tips in your potatoes and broken off blossoms take a look for the TPB. Of course, when it destroys the blossoms of eggplants and peppers the concern is even greater. If you have good looking plants and no fruit, look for the TPB.
Control for TPB is very difficult because they feed on about 300 different species of weeds and are everywhere. You can kill the ones on your crops with a good pyrethrum spray, but there will likely be new ones flying in soon. Still, if you have it very bad, I suggest that you spray at least once or twice to get a crop. Row covers will work if you get them on before the TPB finds the crop.
They are still active in potatoes, beans, apples and strawberries. Nymphs are present now too. I saw a strawberry field with pretty bad symptoms. Remember, you want to be scouting for this pest. Once you see the symptoms (yellow streaking, browning edges of the leaves) it may be too late. The insect feeds by sucking and it injects a toxin that clogs the food conducting tissue of the plant as it feeds. Once this happens it can not be reversed. If you see many of these in your crops I suggest you spray Pyrenone.
Vines are taking off, and many fields are moving into blossom and fruit set. This is when weed control—or lack of it—shows. And, unfortunately, when it’s too late to take care of weeds that escaped early cultivation or herbicide treatments.
Powdery mildew has been reported in Massachusetts. We did not find it in most scouted fields this week, but growers should be watching for it. Symptoms are whitish, talcum-like powdery fungal growth on both upper and lower leaf surfaces, petioles and stems. These are usually found first on older leaves, shaded lower leaves, or undersides of leaves. It may occur first in older plantings.
Rotation only works fairly well because of disease susceptibility of many weeds but be aware that the spores do overwinter on the crop debris. Do not compost it unless you are sure your pile gets hot.
Sulfur will work to suppress the spread but you must keep new tissue covered before the spores land on it.
Late blight has been reported in Central Aroostook County, northern portion. Our office has not confirmed the disease, but with all the experience we have had with the disease, there is little reason to doubt the find. The infection likely occurred June 30 and the late blight appeared July 7. Being spotted in the field the week of July 12 means that there have been one minor and one major infection period since the disease occurred. There is little reason to panic. Look closely at your fields and keep on schedule if you are spraying with copper. We need to realize that we are going to have to expect late blight most years. These mid and late season and especially these small infections are relatively easy to manage. Mature plants are not that attractive to the pathogen - it likes rapidly expanding new leaves. With the recent rainfall in the county, all areas have been conducive for the development of the disease. This is an important time to be scouting for potato late blight! The earlier the disease is found, the more options that you have for control.
European Corn Borer:
Peak moth flight has occurred; moth catches are rapidly declining. Damage from untreated borers or escapes will appear as a wilting branch on the plant with a small entry hole visible. The small entry hole will usually be at a leaf axil and have frass, which will look like sawdust on the hole. Damage has started to appear.
Adult potato leafhoppers are continuing to be found from Central Maine to the St. John Valley. Nymphs are being found in Central Maine and one field has exceeded threshold levels for nymphs. This is a situation that warrants close scrutiny and careful scouting.
Tarnished Plant bug:
Tarnished plant bugs are currently active in some fields. The populations in some fields are some of the highest that we have seen in recent years. These insects are generally not an economic threat, but at high populations, they can cause problems. Symptoms of plant bug feeding are wilting leaflets with a small brown "sting" mark at the base of the leaflet. Heavy populations can reduce yields.
Colorado Potato Beetle
They are still active but have not seen very bad infestations. One grower reports that the row of beans next to the potatoes is repelling the CPB. Has anyone else seen this? Please get back to me.
Early corn harvest continues this week in southern and central Maine, while late planted corn is still in the whorl stage. Dry conditions are taxing irrigation resources in many areas. Insect pressure remains low.
Moth captures were lower in most locations this week. But be on the lookout. At any time there could be a big inflight. We are involved in a project testing an oil applicator that was developed by Ruth Hazzard and using a mixture of corn oil and a concentrated Bt (Condor) (If you want the recipe get back to me). I have been playing around with this at home over the years and have had good results. The key is to time the application of the mix (get it right into the silk channel) with moth captures in pheromone traps. If moths are being caught, Ruth recommends applying the mix after 50% of the silk wilts. Remember, the CEW lays its eggs on fresh silk so there is no concern about corn with brown silk or no silk. If there is report of CEW when you have green silk, you may want to try this.
If you do not have your own trap be sure to call the corn hotline (933 4647), get Dave Handley’s Sweet Corn IPM Newsletter (call Highmoor Farm Experiment Station at 933 2100), or check the Pest Management Office Web site (http://pmo.umext.maine.edu). Dave’s most recent newsletter had a list of Bt products.
European Corn Borer
High numbers of ECB moths continue to be caught in pheromone traps at some locations, but counts were generally lower this week. If moths are being caught in your area and you have green silking corn you may want to try the Bt mix. Also, if more than 15% of your corn in the pretassel stage shows ECB damage (tiny shot holes in the unfolding leaves) then you may want to spray a Bt.
Moth captures in pheromone traps increased this week, but feeding injury on pre-silking corn is still very low.