Vegetable Crop Insect Scouting

David Owens, Extension Entomologist;

Sweet Corn
Cooler evening temperatures this week have helped reduce moth catches in our traps considerably. However, there is still quite a bit of variability out there, and fresh-silking sweet corn is the by farm more attractive to moths. The decreased temperatures also mean that a maximum 3-day spray schedule should be pretty safe. It takes earworm eggs 3 days to hatch when temperatures are below 82 degrees.

This is the last week in which traps will be maintained. Many thanks to Richard Monaco, Jon Baker, Joseph Deidesheimer, and Harry Thompson for faithfully servicing the traps this season. Many thanks also to our cooperators for allowing us to place traps and siphon electricity for the blacklights. Besides aiding sweet corn producers at the trap location and their nearby locale, the trapping network has also helped guide field crop producers, alerting them to the unusually high moth activity in the early and main part of the season. We also used the trap network to time our vial testing. If you would like to see additional insect species included in our regular trapping program or would like to receive direct updates when traps are serviced, please send me a message at


Moth counts from Thursday are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 3 37
Harrington 1 15
Milford 8 23
Rising Sun 4 51
Wyoming 3 47
Bridgeville 1 25
Concord 1 21
Georgetown 1 37
Greenwood 2  
Laurel 4 42
Seaford 2 18
Trap Pond 6 3
Lewes 5 48

This season, we examined rye strips in early May and watermelon fields soon after they were transplanted for spider mite activity. When sampling the rye strips, 3 row feet of vegetation around the edges and in the interior of the field were clipped, bagged, and examined for spider mite presence. We did not find spider mites when we sampled. Of the fields we routinely sampled after transplant, fields that had spider mites present in the interior in the month of June most likely came in with the transplants. These fields also had some of the highest mite activity during July and early August. Now that field operations in our early fields are winding down, some folks are starting to think about cleaning the field up for its next crop. We should also be thinking about cleaning up transplant houses and keeping them clean. Spider mites will use vegetation and winter annual weeds that are beginning to germinate as reproductive hosts and overwintering sites. Mites will begin to physiologically prepare for winter soon, after the autumnal equinox. Overwintering mites are harder to kill with pesticides and can survive longer periods without food. Cleaning up transplant houses and preventing weeds from growing in or immediately around them will go a long way towards keeping next year’s mites in check.

Lima Beans
Continue scouting for corn earworm and soybean looper. Pyrethroids alone have been inconsistent with earworms, and soybean loopers are resistant to them.