Vegetable Crop Insect Management – June 24, 2016

Joanne Whalen, Extension IPM Specialist;

Populations of cucumber beetles vary from field to field but higher populations are still present in fields with a history of problems. Fresh market cucumbers are susceptible to bacterial wilt that is vectored by the beetles, so treatments should be applied before beetles feed extensively on cotyledons and the first true leaves. Although pickling cucumbers have a tolerance to wilt, a treatment may still be needed for machine-harvested pickling cucumbers when 5% of plants are infested with beetles and/or plants are showing fresh feeding injury.

Lima Beans
Be sure to watch for spider mites, especially in dry land fields. Controls are only effective if treatments are applied before populations explode. Labeled materials include dimethoate, Hero (zeta-cypermethrin + bifenthrin), bifenthrin (numerous trade names are available), and Acramite ( bifenazate). Be sure to check the labels for rates and restrictions, including the minimum gallons per acre for ground and aerial application.

Continue to scout all melons for aphids, cucumber beetles, and spider mites. Economic levels of all three insects have been found in fields this past week. When fields are blooming, be sure to consider pollinators when making an insecticide application as well as read all labels for pollinator protection statements and restrictions. We continue to see an increase in spider mite populations in the earliest planted fields. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite, Agri-Mek, Oberon, Portal and Zeal are miticides labeled on melons for mite control. Be sure to read all labels carefully for rates and restrictions since some are restricted to only one application as well as ground application only.

As soon as the first flowers can be found, be sure to consider a corn borer treatment. Depending on local corn borer trap catches, sprays should be applied on a 7 to 10-day schedule once pepper fruit is ¼ – ½ inch in diameter. Be sure to check local moth catches in your area by calling the Crop Pest Hotline, (302) 831-8851, or visiting our website at .

Continue to scout fields for Colorado potato beetle (CPB) and leafhoppers. Adult CPB as well as the small and large larvae can now be found. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. As a general guideline, controls should be applied for leafhoppers if you find ½ to one adult per sweep and/or one nymph per every 10 leaves.

Snap Beans
Continue to sample all seedling stage fields for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by one third. As a general guideline, once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Sprays will be needed at the bud and pin stages on processing beans. After the pin spray on processing beans, the spray schedule will be determined by a combination of moth catches for corn borer and corn earworm and field scouting.

Sweet Corn
The first silk sprays will be needed for ear feeders as soon as ear shanks are visible. Be sure to check both blacklight and pheromone trap catches since the spray schedules can quickly change. Trap catches are generally updated on our website ( and the Crop Pest Hotline (302-831-8851) by Tuesday and Friday mornings. Information on how to use the trap catch information in combination with field scouting can be found at In addition to corn borer and corn earworm, you will also need to start scouting whorl stage corn for fall armyworm larvae. A treatment should be considered for whorl feeders when 12-15% of the plants are infested. Since fall armyworm feeds deep in the whorls, sprays should be directed into the whorls and multiple applications are often needed to achieve control.