Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Spider Mite Alert

New this year for us is participation in Syngenta’s Pest Patrol (https://www.syngenta-us.com/pest-patrol) a text to voice mail service that alerts subscribers when a new message has been posted that they can listen to on their phone. Subscribing is free, and the only time you are alerted is when a new post has been made available on crops that you select.

This week we have had several calls and field visits regarding spider mites. Recent rains have rejuvenated some of the weeds that spider mites are feeding on but beware another stretch of hot dry weather. Under hot dry weather, mite populations can increase 10x per week. If you are not using any sort of magnification, it can be almost impossible to see the eggs and early instar spider mites under leaves. I like to use headband magnifiers such as Donegan’s OptiVisor. Although it only gives up to 3.5x magnification, it has a nice field of view and depth of field. While looking for stippling can be helpful, and often an indication of an infestation, sometimes older leaves do not reveal stippling until large mite populations are present. If you see stippling on younger leaves, check the undersides of older leaves carefully.

In tomato, sample a mid to upper canopy terminal leaflet. Thresholds in tomato and eggplant are 4 mites per leaflet. On legume vegetables, thresholds are 20 mites per leaf before podding. Watermelon thresholds are between 20-30% crowns infested with 1-2 mites per leaf early, and 50% of terminal leaves later in the season. In the MidAtlantic Commercial Vegetable Production Recommendations Guide, the various miticides are also ranked according to bee toxicity. As always, read product labels carefully. Generics may have different use rates and even different formulations. Abamectin labels often require the use of an adjuvant. Thorough coverage and higher water rates will help improve efficacy.

Snap Beans

Earworm counts across the state have declined to low numbers, and we have not yet captured a European corn borer from 6 pheromone trap locations. However, damaging levels of leafhoppers are present in some fields, along with hopperburn yellowing on leaf margins. Treatments are warranted if there are more than 5 leafhoppers per sweep.

Squash

Continue scouting for squash bug egg masses underneath leaves. Thresholds are 1 egg mass per plant and begin treating when eggs begin hatching. In small plantings, sprays targeting squash bug will also help prevent squash vine borer attack. Pay special attention to treated plantings in mid-July onward for aphids.

Scout pumpkins for seedling pests, especially if seed was not treated with Farmore FI1400. I enjoy growing heirloom type winter squash and was recently loathe to see some cutworm damage in my field.

Sweet Corn

Moth counts continue to decline. Traps are checked Mondays and Thursdays, with data uploaded to our website by the following day: https://agdev.anr.udel.edu/trap/trap.php. Most sites would indicate a 4-5 day spray schedule. Keep in mind though that we do not move our traps and not all are immediately next to silk-stage sweet corn, which is the most attractive habitat for earworm. Thursday trap counts are as follows:

Watermelon

In addition to spider mites, Lepidopteran pests are starting to show up. We have seen an increase in various ‘green worms’ and have seen the occasional yellow striped armyworm in fields. Be sure to scout fruit for signs of rind feeding. As we move into July, we have a few interesting worm options to choose from, including diamides (some of which have decent cucumber beetle activity) and a diamide abamectin premix (Minecto Pro). Another excellent worm control product, Radiant, is also very good against thrips.