Vegetable Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Sweet Corn
Moth counts are variable in pheromone but pay attention to blacklight trap captures. Our thresholds for blacklight traps can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/silk-stage-sweet-corn/. Blacklight traps with counts of 2 or greater on Thursday (3 nights) would indicate a 3-day spray schedule.

Begin scouting whorl stage sweet corn for fall armyworm. Typically, this pest shows up in whorls around the middle third of July but may be a bit earlier this year. Look for windowpaning in the whorl leaves and light brown frass pellets. Spotted cucumber beetle will also cause a similar windowpaning feeding but will leave a dark green frass that has a narrower elongated look.

For this week, we were only able to test 16 cypermethrin moths with 27% survivorship, a bit greater than last week. This week, all of our pyrethroids had equal survivorship. With hot weather, it may be best to go with a slightly more conservative spray schedule of 3 days right at the beginning of silking. If the first application is made at about 10% silk, the field may be at full silk after 3 days. It also only takes 2 days for earworm eggs to hatch under high temperatures.

Thursday trap counts are as follows:

Cucurbits
Striped cucumber beetles have just begun emerging from the soil. At this time, thresholds are 2 per plant. Assail and Harvanta provide excellent to good control of striped cucumber beetle; Harvanta is also excellent on Lepidopteran rind feeders. Scout watermelon rinds for signs of insect feeding. Leps will leave smooth, meandering scars whereas beetle scars will have a more textured, ‘dirty’ appearance.

Squash bug populations are increasing rapidly. The threshold is 1 egg mass per plant, by the time this is reached, you may need to consider an initial spray and a follow up application 7-10 days later. Pyrethroids, acetamiprid, and Sivanto should all provide good to excellent control of squash bug. The pyrethroids have the added benefit of controlling squash vine borer; acetamiprid has the added benefit of controlling cucumber beetles. If using a pyrethroid, be sure to scout plants in a couple of weeks to make sure you have not flared up an aphid outbreak.

Several reports came in of folks either making or getting ready to make a second miticide application on watermelon. This is a bit early for 2 applications. Of the miticides I have tested, abamectin has been the most consistent and efficacious, followed by a ‘good tier’ consisting of Portal, Zeal, and Banter (bifenazate), and then Oberon. Oberon and Zeal are target egg production and juvenile development; it may be interesting to tank mix those with something that provides more mobile knockdown like a bifenthrin or dimethoate, but I have not tested this. I do not recommend either material for mite control alone. We have also observed poor mortality in striped cucumber beetle populations following a bifenthrin application, decreasing potential side-benefits. These materials are going to be slower in reducing mite populations.

Magister is in the same MOA class as Portal. Acramite (bifenazate) and Kanemite (acequninocyl) are in a similar MOA class. Of the miticides, abamectin, etoxazole, and spiromesifen (Oberon) are translaminar. Do not mix them with stickers or sticky fungicides such as chlorothalonil.

Peppers
Begin scouting for beet armyworm activity. Females lay egg masses and young larvae cluster together and web leaves together as they feed. They can cause significant, localized defoliation. Beet armyworms have a small black spot above the second pair of legs behind the head and are resistant to pyrethroid insecticides.