Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Sweet Corn

Our early July corn earworm flight continues, with some sites recording unusually intense activity. I am concerned that we have a relatively strong flight for this time of year right when field corn is silking, possibly setting us up for a robust August flight. We have tested 90 moths against cypermethrin-treated vials this week and had a survival rate of 45%. This is considerably higher than when we started testing in early June. Pyrethroids should not be relied on alone to control earworm. Also pay attention to young sweet corn for signs of armyworm infestation. Look for windowpaning on the innermost whorl leaves. By the time large holes are noticed in the whorl, the larva may be too deep to get good coverage or may have already left the plant to pupate. Thresholds for young plants are 15% infested whorls. This rises to 30% until tassel push before decreasing to 15% infested emerging tassels. To date, we have not captured any European corn borer in our pheromone traps. If you are using a relaxed spray schedule right now, check your field for sap beetle, especially as silks begin wilting and browning. You may need to make an application specifically targeting them.

Thursday corn earworm trap captures are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 3 88
Harrington 1 20
Milford 1 31
Rising Sun 0 30
Wyoming 1 32
Bridgeville 0 41
Concord 1 15
Georgetown 0 31
Greenwood 1 22
Laurel 3 131
Seaford 5
Lewes 5
Millsboro 1 8



Continue scouting watermelons for rind feeding pests. First-generation cucumber beetle adults are coming out of the soil. New young beetles have whitish stripes on the wings which gradually turn to the characteristic yellow. They like to feed on flowers, and because flowers are only open in the morning, you can look at the flowers to gauge cucumber beetle activity. Cucumber beetles are best controlled by acetamiprid (Assail, premixes like Savoy, and other generics). Worm pests are active in many fields. If you see large meandering rind feeding paths, it is probably the work of various worm species. Active worms include corn earworm, yellow striped armyworm and beet armyworm, with other species mixed in. Earworms and beet armyworm are more difficult to control with pyrethroids, other excellent materials include diamides (Coragen, Besiege, Harvanta, Exirel, and Minecto Pro), spinosyns (Radiant), growth regulators (Intrepid), and indoxacarb (Avaunt). Harvanta and to some extent Exirel, have activity on cucumber beetles. Minecto Pro has abamectin in it and is an excellent miticide.


Continue scouting for beet armyworm. Female moths lay egg masses, so often several plants in a row will be heavily damaged as larvae grow and disperse. Pyrethroids are ineffective on them and have the potential to flare up aphid outbreaks.