Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Cucurbits
Cucumber beetles continue to move into fields. It is important to base a treatment decision from 5 to 10 locations per field. I visited a couple of fields this week where cucumber beetle activity was heavy, but only on a couple of rows and a few plants within those rows. For watermelon, we use an action threshold of 2 beetles per plant for young transplants. Other states use a threshold of 5 beetles per plant once vines start running. Unlike watermelon, cucurbits such as summer squash, cucumber, and cantaloupes are susceptible to bacterial wilt. These crops are also more attractive to cucumber beetle than watermelon, thus you may need to treat them more often or see more aggressive cucumber beetle populations. Pumpkins are not very susceptible once they have two true leaves (not counting the cotyledons), and so a seed treatment should provide sufficient control to avoid bacterial wilt. We have been relying heavily on the Group 4A chemistry early, products like imidacloprid, acetamiprid, and thiamethoxam, followed by Group 3 pyrethroids late. There are a couple of other chemistries that may provide good cucumber beetle control: Lannate, Sevin XLR plus, and two diamides, Exirel and Harvanta. Our group is in the process of collecting cucumber beetles from across the area to test susceptibility to the commonly used insecticides. If you have a treatable population, please let me know before or within 1 day of treating and I will gladly take some cucumber beetles off of your hands. Thanks!

Spider mites can be found in some fields, most likely coming in with the transplants. At this stage, you will see the light yellow stippling on the leaves. This stippling is not as apparent on older melons once the leaves thicken up until there are very high populations underneath the leaf. Agrimek or other Abamectin containing Group 6 products can provide excellent control and are systemic miticides. They are hard on bees, so if you are using them during the season, the best window for using them is prior to bee arrival and to apply in the evening when pollinators are not as active.

Sweet Corn
Sweet corn pheromone and blacklight traps are checked twice weekly on Mondays and Thursdays. By Tuesday and Friday morning, data is uploaded to our website: https://agdev.anr.udel.edu/trap/trap.php. For reference, action thresholds based off of blacklight and pheromone trap can be found here: http://extension.udel.edu/ag/insect-management/insect-trapping-program/action-thresholds-for-silk-stage-sweet-corn/. Silking sweet corn is highly attractive to moths, a trap that is nearby but not adjacent to sweet corn may not be entirely representative of the population in your block. Thursday trap counts are as follows: