Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Cucurbits

If watermelons haven’t been treated for cucumber beetles, but have been treated with pyrethroids earlier this season, be sure to scout for aphids. This year at the research station we have had very low levels of cucumber beetle or worm feeding on rinds, but I treated my melons with a pyrethroid to flare up mites. Aphids are now present in larger numbers than the previous couple of seasons. Continue scouting for mites, paying attention to areas with yellow blotches on leaves.

Pumpkins and late summer squash that have been treated with pyrethroids (often used for squash bug and squash vine borer) need to be scouted for aphids. We have numerous aphid products available. Assail will also pick up cucumber beetles and squash bug; Torac will pick up worms, Exirel, Verimark, Harvanta will pick up worms and beetles, Minecto Pro will pick up mites in addition to the worms and have some effect on beetles. Other products listed in the guide are aphid specific.

Sweet Corn

Scout whorl stage sweet corn for fall armyworm NOW. Look for windowpaning and small sawdust looking frass pellets in the whorl. By the time you see large holes and large frass pellets the worms may be so deep in the whorl that they will be difficult to kill with insecticides. In addition, fall armyworm kicks feeding into high gear the last handful of larval development days. Thus, often when large holes are observed, the larvae are leaving or have left. Keep in mind also that windowpaning with green frass pellets is more indicative of spotted cucumber beetle.

Many if not most of our trap sites are indicating a 3-day spray schedule either by blacklight or by pheromone trap counts. Corn earworm Thursday trap counts are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 2 93
Harrington 1 39
Milford 4 73
Rising Sun 2 43
Wyoming 2 87
Bridgeville 1 33
Concord 2 20
Georgetown 1 78
Greenwood 3 14
Laurel 4
Seaford 1
Lewes 30 (1 night)

 

Pepper

Scout for signs of worm feeding on pepper fruit and beet armyworm feeding in the upper canopy leaves. If defoliation is a threat, remember beet armyworm are resistant to pyrethroids.

Tomato

Continue scouting for spider mites and also consider preventative fruitworm treatments. For spider mites, the threshold is 2-4 mites on an upper canopy leaflet.

Cole Crops

Diamondback moth activity has increased markedly the last week or so with hot dry weather. In Georgetown so far, we have not had much cabbage looper activity. It is very important to check plantings for cabbage looper, as Torac does not have cabbage looper on its label, but it is quite good on other worms and aphids. Harlequin bugs are very active and are best controlled with foliar neonicotinoid or pyrethroid applications. Be sure to use a spreader-sticker adjuvant to counter the effect of the waxy leaves on spray droplets.

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