David Owens, Extension Entomologist, email@example.com
Thresholds for cole crops early are 20% infested plants, rising to 30% infested plants during the midseason, and then falling again below 5% infested plants when the plants begin forming the harvested structures. Besides the usual 4 caterpillar pests that infest cole crops this time of year (imported cabbageworm, diamondback moth, cabbage looper, and cross striped cabbageworm), fall armyworm, corn earworm, and beet armyworm are active. It is important to get a good identification as early as possible because beet armyworm, corn earworm, and diamondback moth are either not or are much less susceptible to pyrethroids than the others. Last year, we had good head injury ratings from Radiant and Rimon. Be sure to read labels carefully, some products may not be labeled for all of the worm pests. The growth regulator insecticides (Rimon, Intrepid, Confirm) work best on small worms. Also scout for aphids and for harlequin bugs. Besiege can pick up worms and harlequin bugs, but not aphids. Voliam Flexi and Durivo should be able to control all three, but pay attention to preharvest intervals. If harlequin bugs are not an issue, and aphids are your primary pest (as in my cabbage in Georgetown) there are a wide range of excellent aphid products available. University of Massachusetts advises a threshold of 10% of plants with at least 1 aphid or 20% of leaves with aphids.
In addition to the sucking bugs (aphids and squash bugs), scout for melonworms. Earlier this week there was a report of a significant melonworm infestation in Illinois, which is unusually far north for this insect. Both melonworm and fall armyworm overwinter in Florida, and melonworm has been active on Virginia’s Eastern Shore since early August. It stands to reason that with weather patterns favoring the fall armyworm migration that has resulted in damaged lawns and treated sod, it is possible that melonworms are also active in our area. Look at the undersides of leaves that have been partially shredded and look at the rinds of pumpkins to determine if they are attacking the fruit.