Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Sweet Corn

Come join us September 13 for a plot and crop tour of sweet corn at the Carvel Research and Education Center starting 4:45 PM. Nate Bruce will discuss crop inputs, Emmalea Ernest will discuss variety selection and heat tolerance, Alyssa Koehler will discuss pathogen management, and yours truly will be discussing his favorite insect of sweet corn – corn earworm, as well as walking through plots.

Continue scouting for fall armyworm and for aphids. Fall armyworm can infest plants at any growth stage. Egg masses look like grayish white pieces of fluff on leaves and may continue up to several hundred eggs. Neonates disperse on silk threads soon after hatching leading to circular areas in fields with heavy feeding damage. Fall armyworm can be most damaging when egg masses hatch just before silking, as the caterpillar will start to move into the husk leaves and silk channel, potentially before earworm spray programs begin. Also continue scouting for aphids about 10 days after silking.

Thursday earworm trap captures are pretty similar to what we have experienced over the previous two weeks. The only good news is that we are starting to see some more ‘older’ moths in traps.

Tomatoes

With high earworm trap captures, the risk for fruit damage is elevated and worm sprays should continue. There are other worms that will also get into tomatoes, but earworm is the hardest to kill with chemistry due to pyrethroid resistance. Use high volume, high pressure to ensure good interior fruit coverage. Continue monitoring fruit for signs of stink bug damage. Stink bug damage will look like white, cloudy, irregular splotches on fruit surfaces.

Peppers

Continue scouting for beet armyworm, aphids, and stink bugs. Stink bugs are best controlled with pyrethroid and neonicotinoid insecticides. Aphids can be flared up by pyrethroids, but fortunately there is a large number of products labeled for aphid control. Beet armyworm is also resistant to pyrethroids. It lays eggs masses like fall armyworm. However, larvae stick together and feed in clusters before dispersing, leading to smaller portions of heavy defoliation.

Two oddballs were reported this week: whiteflies and broad mites. Broad mites are extremely small mites that cause distortions of leaves and russeting on fruit. If pepper leaves exhibit distortions and curling, place it under a microscope to look for broadmite adults and eggs. A report was received earlier this week of whitefly infestation in pepper. Suggested thresholds range from 1 whitefly per leaf on tomato to 4 whiteflies per leaf in pepper. I suspect that whiteflies, while present, are not going to cause significant injury to the majority of fields that have them at this point in the season.

Pumpkins and Watermelons

Continue scouting for rind damage from worms and from striped cucumber beetle. Second generation adults are emerging from soil and actively feeding to bulk up for winter. Also scout for aphids, particularly in pumpkins where honeydew and sooty mold on the fruit may be an issue. Aphids can be flared up by earlier pyrethroid use.

Cole Crops

Curiously, cabbage looper has not been observed this season in Georgetown plots or in Dover plots. Diamondback moth is very active, especially with recent dry, warm weather. Other pests that need to be scouted for, particularly with young transplants, are flea beetles. These are small black beetles with jumping hind legs. Depending on the species, there may be a yellowish orange stripe on either side of the elytra. Thresholds for flea beetles are 1 per transplant or 5 beetles per 10 plants. They will lay eggs in soil and larvae can also cause signficant root injury. Flea beetles can be controlled with pyrethroids, neonics, Torac, and diamides. Of those, neonics will control aphids (also a potentially significant pest right now and can reduce cabbage head formation) and harlequin bugs, Torac will control worms (with the exception of cabbage looper), and the diamides will control worms and aphids (unless field history suggests diamondback moth resistance).