Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Scout greenhouses now for aphids and spider mites on transplants. Aphids can be easily controlled with tray drenches of a neonicotinoid. A tray drench should also prevent cucumber beetle damage on transplant wagons but tray drenches have limited residual activity once the transplants are planted and growing. Be sure to read the labels carefully to ensure that you have enough active ingredient left for a cucumber beetle application in the drip lines if needs be next month. For greenhouses with spider mite activity, the easiest time to treat the transplants is while on the transplant wagon.

Asparagus beetle activity is increasing. Check both field edges and field interiors. On a recent field visit, 14% of asparagus spears had a beetle present and 4% of spears had eggs present along the field edge bordering a road and an overwintering habitat, while just another 100 feet into the field the infestation % dropped off significantly. Eggs look like small dark cylinders sticking out of the spear at a 90 degree angle (Figure 1). Thresholds from Michigan State University suggest a lower threshold than previously reported; 5% of spears with adults and 2% of spears with eggs. Labeled materials include carbaryl, (pay attention to rates pre-harvest) malathion, pyganic (OMRI) and permethrin.

Figure 1. Asparagus beetle eggs on an asparagus spear

Figure 1. Asparagus beetle eggs on an asparagus spear.

Cole Crops
Diamond back moth is now active in addition to imported cabbageworm. Thresholds at this stage are fairly high at 20% infested seedlings of any caterpillar pest. If at all possible, avoid broad spectrum insecticides so as to conserve beneficial wasps as much as possible. Last year, we installed a cabbage plot where a parasitoid wiped out every single diamondback caterpillar early in the crop stage thus keeping even untreated plots clean at harvest. If using Bt, coverage is especially important. Bt can be quite effective on smaller plants when targeting smaller worms. Bt aizawai strains tend to be a bit more effective than kurstaki strains. Other cole crop pests active right now include flea beetles (seen primarily in brassica cover crop). If flea beetles and worms are present, diamides and spinosyns are effective on both among the more ‘narrow spectrum’ materials and Torac is also quite effective but a bit more broad spectrum.

Seedcorn Maggot
Last week, Jerry Brust had an excellent column on seedcorn maggot. Looking ahead at the forecast, there is a chance of rain this weekend followed by cooler temperatures and possibly more rain by the end of the week coming. These conditions will increase the risk for seedcorn maggot injury. Consider a neonic seed treatment and for any recently transplanted vegetables onto plastic, examine plant holes for adult fly activity. Adult activity is an indicator of egg laying. While there are no rescue treatments available once maggots begin working on the roots and stems below ground, it may be possible to suppress them by running insecticide through the drip lines, provided the maggots have not begun damaging and entering the stems. Such an application might still provide residual control for when cucumber beetle becomes active (usually between the 2nd and 3rd week of May, but probably will be sooner this year).

Potato and Tomato
Scout for Colorado potato beetle on new potatoes and high tunnel tomato or egg plants for which the sides were rolled up during last week’s heat. It has been warm enough several days over the previous couple of weeks for beetles to fly and disperse long distances.

Aphids are beginning to fly into pea fields now. If a field has experienced prior SCM stress, pay attention to water and fertility regimens to reduce stress on the plants as much as possible.

Sweet Corn
The 1971 season marked the beginning of the University of Delaware IPM program. This week, pheromone and black light traps were deployed once again for monitoring various pests including corn earworm, European corn borer, and the stink bug complex. This year, we were able to locate our initial set of traps near more sweet corn fields than in previous years. Many thanks to hosting farmers and to Richard Monaco for supporting and servicing the trap network. Trap counts will be submitted in the WCU beginning in early June.