Vegetable Crop Insects – May 13, 2011

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Leafminers in Vegetable Crops
Each spring, we receive reports of leaf miners attacking spring planted vegetable crops. There are a number of potential species that attack vegetables including the vegetable leafminer, serpentine leaf miner, spinach leafminer and beet leafminer. Leaf miners can be difficult to control and we have limited experience with control strategies in our area. The following links provide information on some of the potentially important species:
http://entnemdept.ufl.edu/creatures/veg/leaf/vegetable_leafminer.htm

http://entnemdept.ufl.edu/creatures/veg/leaf/a_serpentine_leafminer.htm

http://www.umassvegetable.org/soil_crop_pest_mgt/insect_mgt/beet_leafminer.html

Cabbage
Continue to scout for diamondback and imported cabbageworm larvae. Economic levels of diamondback larvae can be found. A treatment should be applied when 5% of the plants are infested and before larvae move to the hearts of the plants.

Melons
Continue to scout all melons for aphids, cucumber beetles, and spider mites. Economic levels of aphids can be found in some fields but beneficial insects (lady beetles and parasitized aphids) can also be found and in many cases they are helping to manage populations. As a general guideline, a treatment should be applied for aphids when 20 percent of the plants are infested, with 5 aphids per leaf and before significant leaf curling occurs. Low levels of spider mites are also being found in a few fields.

Peppers
As soon as plants are set in the field, begin sampling for thrips and corn borers. On young plants, corn borer larvae can bore into the stems and petioles. In areas where peppers are isolated or corn is growing slowly, moths are often attracted to young pepper plants. As a general guideline, treatment may be needed if there is no corn in the area or you are using rye strips as windbreaks. You should also look for egg masses. At this time of year, thrips can damage peppers by vectoring tomato spotted wilt virus and by causing direct plant damage. Although there are no available thresholds, a treatment may be needed if you see populations increasing.

Potatoes
Continue to sample for Colorado potato beetle adults and egg laying. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. Corn borer moths are being found in BLTs throughout the state; however, flights are still low. A corn borer spray may be needed 3-5 days after an increase in trap catches or when we reach 700-degree days (base 50).

Snap Beans
All fields in the seedling stage should be scouted for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Be sure to also watch for bean leaf beetle feeding. Damage appears as circular holes in leaves and we have seen significant damage in recent years on the earliest planted fields. As a general guideline, a treatment should be considered if you defoliation exceeds 20% prebloom.

Sweet Corn
Continue to sample for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding. In order to get an accurate estimate of flea beetle populations, fields should be scouted mid-day when beetles are active. A treatment will be needed if 5% of the plants are infested with beetles. Be sure to also watch for corn borer in the whorls of the earliest planted fields. A treatment should be applied if 15% of the plants are infested.

 

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