David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Corn earworm trap counts are high, and for only the second time this summer, we have caught a European corn borer in a pheromone trap! They do exist!
During the first 10 days of silking with temperatures above 82 degrees, a 2-day spray schedule following a pyrethroid and a 3 day spray schedule following a chlorantraniliprole application is advisable, especially at sights with very high moth activity. Last week’s Weekly Crop Update had a very in-depth article on earworm management. With frequent applications such as these, be sure to scout for aphids, especially about 10 days before harvest so that if a population begins developing, a high rate of Assail can be used (7 day pre harvest interval). We are in the process of conducting adult vial pyrethroid resistance tests, and so far, cyfluthrin is showing a greater level of activity against corn earworm than lambda cyhalothrin, similar to field trial results from the last couple of seasons. While I recommend the same spray schedule regardless of the pyrethroid used, it may be that cyfluthrin in the spray program might prevent a couple of misses and provide just a little bit more efficiency.
Trap counts can be found at http://agdev.anr.udel.edu/trap/trap.php, and thresholds can be found at: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/silk-stage-sweet-corn/.
Thursday trap counts are as follows:
| Trap Location |
BLT CEW |
Pheromone CEW |
| 3 nights total catch | ||
| Dover | 6 | 156 |
| Harrington | 2 | 71 |
| Milford/Canterbury | 4 | 165 |
| Rising Sun | 9 | 65 |
| Wyoming | 8 | 153 |
| Bridgeville/Redden | 1 | 93 |
| Concord | 7 | 44 |
| Georgetown | 2 | 82 |
| Woodenhawk | 2 | 78 |
| Laurel | 10 | 117 |
| Lewes | – | – |
Snap Beans and Lima Beans
Scout beans for worms or consider a treatment if a lot of moths are observed in the crop. Unlike sweet corn and unlike European corn borer, no threshold is available for timing sprays on either crop for this pest, except a black light threshold that to be honest, we have not reached or exceeded in years upon years. In lima bean fields, a beat sheet or shaking plants and counting earworm on the ground can be used to estimate population. Thresholds in lima beans are 1 earworm per 6 row feet. Labeled insecticides include IPM and bee friendly materials such as Avaunt, Vantacor, Coragen, Blackhawk, Bt, and high rates of Intrepid. Of these, Coragen and Vantacor are going to provide the longest residual control.
Stink bugs may also require treatment and complicate matters a bit. Stink bugs are tanks. The best pyrethroid is bifenthrin. Elevest is a chlorantraniliprole and bifenthrin premix which may be handy.
Tomatoes
Brown stink bugs are still active in tomatoes and can be controlled with either a bifenthrin application or a dinotefuran application. Begin incorporating worm materials in a spray program. Earworms and tobacco budworm are actively laying eggs in flowering tomatoes.
Cucurbits
Squash bug continues to increase population. Use high pressure to get spray droplets to where adults are hiding under leaves, near the base of the plant, and remember, fi you are targeting mostly adults and egg masses are present, a follow-up spray about 7-10 days later may be necessary.
Spinach
There is quite a bit of webworm activity in Georgetown this year. If growing spinach, scout for webworm. If growing spinach, scout for small caterpillars.