Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

It’s starting to get a little buggy out there.

Melons
Striped cucumber beetle, Lepidopteran rindworms, and spider mites are all very active in fields. Beet armyworm continues to pop up in fields with pigweed. On pigweed, look for intense shredding of the upper leaves, but note that this can be confused with webworm. Flea beetles on pigweed leave large round to rectangular holes. Keep a close eye on fields with mites going into harvest. Harvesting stresses vines, and stress combined with high heat favors mite population growth. Also, mites will hitch a ride on equipment and workers, so if hotspots were confined to one portion of a field they may spread to a much larger area.

Both melon and green peach aphids are reappearing in vining cucurbits. Aphid colonies reproduce quickly, especially in fields that have been treated with pyrethroids that knock out lady beetles, pirate bugs, lacewings and wasps. Large aphid colonies can weaken vines toward the end of the season, and their honeydew secretion can coat fruit resulting in sooty mold growth. This can be especially problematic in pumpkins. Melon growers may be considering a treatment for striped cucumber beetle. Assail will take care of aphids. For those with mites and worms, Minecto Pro is labeled for aphids. For those with just worms, diamides are good options. There is a wide range of other products that are more aphid specific.

Cole Crops
The final member of the cole crop worm complex was spotted earlier this week in a kale plot in Georgetown: cabbage webworm. Be sure to scout transplants carefully, worms can quickly do heavy damage on small plants. Last year, about 10% of my transplants turned into spears almost overnight because a yellow striped armyworm found the plants as soon as I put them out to harden off. Cabbage looper is very active, but if hot dry weather persists into the fall, diamondback moth may become more abundant.

Sweet Corn
The 2020 moth flight is beginning. Some trap locations are high while others are low to moderate. Even traps that I have next to silking corn are highly variable in relatively short distances (less than 1 mile). Fall armyworm has reached threshold levels in spots throughout the state. Females lay egg masses that contain dozens to a couple of hundred eggs. Larvae crawl or disperse on silk threads to neighboring plants, leading to circular areas of a few to several dozen infested plants. When opening up whorls, you may see green fall armyworm color morphs, particularly on small worms. Fall armyworm also has a black spot on the side of the body, but this spot is a little larger and farther back than that of beet armyworm. Armyworms feed deep in the whorls where it can be difficult to reach with an insecticide. Nozzles directed over the whorl and applying product through a minimum of 50 GPA will help. Good control options include Rimon, Avaunt, and Radiant. Lannate can give good control if worms haven’t gone deep, or if worms are exposed when the tassel pushes them out. Save Besiege or Coragen for silking. We are limited with how much active ingredient can be applied per acre per year, and we need that chlorantraniliprole for earworm protection now that the moth flight is beginning.

When scouting, you may see rectangular ears that are window-paned or partially so. Spotted cucumber beetle will feed on corn and do this, but it is of little consequence. If you are unsure of the culprit, look for small, rectangular dark green frass and the absence of increasingly severe damage from the outer to the inner whorl leaves.

Aphids may start showing up in sweet corn. The best options for aphids include Lannate, Sivanto, and Assail. Sivanto and Assail do not have any worm activity, but both are far less toxic to workers and to beneficial insects. Spider mites might be present along field edges. If you need to treat for spider mites, in addition to Oberon and Brigade, Zeal was recently registered for use in sweet corn.

Thursday corn earworm moth capture is as follows:

Pepper
Continue scouting for beet armyworm and yellow striped armyworm. While yellow stripes are fairly easy to control, beet armyworm is resistant to pyrethroids. Also be aware that aphid populations are starting to show up in other vegetables; aphids are favored by frequent pyrethroid applications. Corn earworm flight is starting to pick up. Use a beat sheet to determine if worms are present. No thresholds have been worked out for pepper.

Beans
Continue scouting for potato leafhopper. Thresholds are 100 per 20 sweeps. Adults will quickly fly out of the sweep net, and some of the smallest nymphs can be quite difficult to see. Spider mites might also build up along field edges. We are limited in good miticides for snaps and limas. Dimethoate can knock them back, but may require more than one application. There should be good soil moisture and plants should be actively transpiring, so wait until the day cools before applying. Kanemite, Acramite, and Magister are all very good, long residual miticides. Magister is unique in that it has powdery mildew activity. Portal is registered for snap beans only.