Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Continue monitoring for spider mites, especially on field edges. With current weather conditions, spider mite populations can increase nearly 10x per week. Spider mite populations are especially likely to explode when plants are carrying a large fruit load. It might be useful to treat with a miticide if a moderate population is present right before harvest activity begins (but within label PHIs). Harvest stresses plants and can result in mites increasing rapidly.

Sweet Corn
Begin monitoring for fall armyworm in whorl stage sweet corn! We have a couple of pheromone traps in Sussex County that have captured a couple of moths. While this may not seem like much, our pheromone traps didn’t capture many last year either despite the severe damage to turf grasses observed.

Corn earworm pheromone trap captures have decreased again. Delaware trap thresholds tend to be on the conservative side, and it may be possible for many areas to be on a 4 to even 5 day spray schedule, depending on the stage of the crop (early silking corn is most attractive to females), previous application (I expect Besiege and Elevest to have greater residual efficacy, based on a 2018 trial), and of course, local trap capture (traps adjacent to silking corn will provide the best read on moth pressure).

Thursday trap captures are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 1 7
Harrington 1 4
Milford 0 7
Rising Sun 1 20
Wyoming 0 1
Bridgeville 0 55
Concord 1 17
Georgetown 0 5
Greenwood 1 8
Laurel 1 17
Seaford 0
Lewes 12


Continue scouting for spider mites. Mite thresholds are 2-4 mites per upper canopy leaflet. It is possible however that intense localized hotspots exist in a planting. Heavy mite populations can also cause a fruit injury that looks very similar to ‘gold fleck’. Use high pressure, high water volume to get as much product to where the mites are located (under leaves). Agri-mek has translaminar activity. Also note the adjuvant requirement on Agri-mek’s label. Other labeled materials include Onager, Nealta, Oberon, Portal, Magister, Oberon, and Acramite. Do not apply Acramite and Kanemite back to back, and do not apply Magister and Portal back to back, they are in the same mode of action.

Scout for mites and for Colorado potato beetles. Eggplant is especially susceptible to mite infestation. Fortunately, there are a plethora of options for mite management. Colorado potato beetles are also highly attracted to eggplant. Destroying nearby non-crop hosts such as horse nettle may help reduce potato beetle infestation in the general landscape. Be on the lookout for orange egg clusters on leaves. There are 8 modes of action available. Rimon, group 15, is a growth regulator and most likely effective on small larvae as opposed to large larvae.

Snap Beans
Corn earworm flight right now is low. Turn scouting attention to potato leafhopper and to spider mites. Spider mites love snap beans, and any snap beans previously treated with a pyrethroid may be at a greater risk of spider mite. Minecto Pro is labled for snap beans and would pick up worms, but the risk of a worm issue is low right now. Dimethoate has efficacy on both leafhopper and mites. If mites are not a significant threat, potato leafhopper is susceptible to pyrethroids. Thresholds are 5 leafhoppers (adults plus nymphs) per sweep. We have had a large stink bug flight in several locations, thresholds are 7 stink bugs per 50 sweeps.