Emily Zobel, Senior Agriculture Agent Associate | ezobel@umd.edu
University of Maryland Extension, Dorchester County
Be sure to check all labels carefully before combining insecticides and herbicides. Thresholds are based on sampling 100 plants (10 plants x 10 locations).
Alfalfa
Begin scouting for potato leafhoppers (PLH). Stubble insecticide applications are rarely needed and seldom provide reasonable control since adult leafhoppers will move out of the field after cutting. A rough threshold estimate is 20 PLH per 100 sweeps on alfalfa 3 inches or less in height, 50 PLH per 100 sweeps in 4-6 inch tall alfalfa, and 100 PLH per 100 sweeps in 7-11 inch tall alfalfa. A more precise threshold chart can be found on Penn State Extension website https://extension.psu.edu/potato-leafhopper-on-alfalfa.
Field Corn
Scout for armyworms and cutworm if growing a hybrid that doesn’t control for them. Treatment threshold for armyworms in corn is 25% infested plants with larvae less than one inch long. Large larvae feeding deep in the whorls will be challenging to control. When scouting for cutworm, check/dig around the base of the plants to determine if cutworms are present and alive. Cutworms tend to be more common in late terminated cover crop, late planted corn fields. Cutworm thresholds are 5% cut plants at V2-V4 or 10% of plants with signs of fresh leaf feeding.
Once plants start to silk, scout for Japanese beetles and stink bugs. For Japanese beetles, the treatment threshold is when there is less than ½ inch of silk and less than 50% pollination, and an average of 2 or more beetles per ear. For stink bugs, the threshold is 1 bug per 10 plants (V1 to V6), 1 bug per 8 plants (V14 to VT), and 1 bug per 4 plants (R1 to R2). Cereal leaf beetle, stink bugs, and Japanese beetles are ‘edge’ pests, so treatment may only be needed around field edges and pivot tracks.
