Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Alfalfa
Begin scouting for potato leafhopper. There’s an excellent threshold table borrowed from Penn State Extension on the alfalfa insect control sheet: https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/pest-management/Insect_Control_in_Alfalfa_-2023.pdf. Thresholds vary tremendously depending on how tall the alfalfa is. Pyrethroids do a good job on potato leafhopper.

Small Grains
A report came in of some localized low level armyworm activity in wheat. Armyworm thresholds are 3-5 per square foot. Examine residue and look for frass. All pyrethroids except Mustang Maxx have a 30-day PHI.

Field Corn
Scout seedling corn for cutworm injury. A second report of cutworm damage came in this week. Pay special attention to fields in which weeds or cover crop were terminated late and close to planting. Cutworms hide during the day in burrows in the soil, coming out at night to feed. Small cutworms will leave symmetrical, parallel holes in the leaf blade, while larger cutworms will cut and partially drag plants under the soil. Thresholds are 3-5% cut plants and larvae are present.

This week’s warm, sunny weather should have allowed corn to resume growth, and corn may quickly outgrow slug injury. When scouting, look at the condition of the whorl leaf, if it is not being fed upon or only slightly, the plants should continue progressing.

Soybean
Scout for slug and seedcorn maggot damage to the stand. Generally, I think of Memorial Day as the turning point for both in which they are less likely to cause injury.

Other defoliators may be active, such as Grasshoppers, cloverworm, and bean leaf beetle. Defoliation thresholds are conservative at 30% of the entire canopy.

Early Season Moth Activity
Many thanks to Joanne Whalen and David Armentrout at UMD for assistance with monitoring pheromone traps.