Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Cabbage
Continue to scout fields for imported cabbage worm and diamondback larvae. The first larvae can be found and sprays will be needed before they move deep into the heads. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae. If both insect species are present, Avaunt, the Bt insecticides, Proclaim, Rimon, Spintor or Radiant have provided control.
Melons
Aphids continue to be found in the earliest transplanted fields. When sampling for aphids, be sure to watch for beneficial insects as well since they can help to crash aphid populations. As a general guideline, a treatment should be applied for aphids when 20% of the plants are infested, with at least 5 aphids per leaf. Foliar treatments labeled for melon aphid control on melons include Actara, Beleaf, Fulfill, Lannate and Thionex. These materials should be applied before aphid populations explode. The Fulfill label states that the addition of a penetrating type spray adjuvant is recommended to provide optimum coverage and penetration. Admire, Platinum and Venom are also labeled at-planting for aphid control.
Peas
We continue to find economic levels of aphids in peas so be sure to sample all fields on a weekly basis. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. When sampling dryland peas, you may want to reduce the threshold, especially if they are drought stressed. Be sure to check labels for application restrictions during bloom.
Potatoes
Continue to sample fields for Colorado potato beetle adults, especially if an at-planting material was not used. Low levels of the first emerged adults can now be found. A treatment should not be needed for adults until you find 25 beetles per 50 plants and defoliation has reached the 10% level. If a neonicotinoid insecticide was used at planting (i.e. Admire, Platinum, Venom, Cruiser or Gaucho), you should not apply a foliar neonicotinoid in season (i.e. Actara, Assail, Endigo, Leverage or Provado). Low levels of corn borer moths have been caught in light traps. 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). If you are scouting for infested terminals, the first treatment should be applied when 10% (fresh market) or 20-25% (processing) of the terminals are infested with small larvae.
Sweet Corn
Continue to scout emerged fields for cutworms and flea beetles. As a general guideline, treatments should be applied for cutworms 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 midday when beetles are active. A treatment will be needed if 5% of the plants are infested with beetles.