Joanne Whalen, Extension IPM Specialist;jwhalen@udel.edu
Alfalfa
The first leafhoppers have migrated into the state so be sure to sample on a weekly basis after the first cutting. Once plants are yellow, yield loss has already occurred. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.
Field Corn
Depending on the location in the state, we can find low levels of both cutworm and slug damage, mainly in no-till corn fields. It is important to check all fields for cutworms, even where at planting treatments were used. The treatment threshold is 3% cut plants in spike to 3-leaf stage corn. In some cases you will need to check fields twice a week to be sure you do not miss an economic population. In addition to cut plants, be sure to watch for leaf feeding, which can be an indication of the potential for significant cutting damage and yield loss.
(http://www.ent.iastate.edu/imagegal/plantpath/corn/bcutworm/1287bwcholes.html)
Small Grains
We continue to find armyworms, grass sawfly, aphids, and cereal leaf beetle (CLB) larvae and in some cases CLB adults still laying eggs in barley and wheat fields. Population levels remain variable throughout the state so scouting fields will be the only way to determine if an economic level is present. Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley. Heavy defoliation of the flag leaf can result in significant economic loss. Armyworms generally begin head clipping when all vegetation is consumed and the last succulent part of the plant is the stem just below the grain head. Larvae can feed on the kernel tips of the wheat, resulting in premature ripening and lower test weight. We continue to see an increase in aphid numbers so you will also need to watch for aphids feeding in the heads of small grains. The treatment threshold is 15-25 aphids per head with low beneficial insect activity.
Soybeans
Seed corn maggot could be a potential problem in no-till soybeans, especially if we see an extended period of cool and wet weather. It could also be a problem in conventional soybeans where a cover crop is plowed under immediately before planting or where manure was applied. All of these situations are attractive to egg-laying flies. Control options are limited to commercial applied seed treatments containing an insecticide and one hopper box material containing permethrin (Kernel Guard Supreme). Labels state early season protection against injury by seed corn maggot.No rescue treatments are available for this insect pest.