Agronomic Crop Insects – May 17, 2013

Joanne Whalen, Extension IPM Specialist;

Field Corn
Depending on the location in the state, we can find both cutworm and slug damage, mainly in no-till corn fields. Although we do not have pheromone traps out to monitor black cutworm moth populations, higher than normal populations are being reported in some areas of the Midwest as well as Pennsylvania. In past years, when populations were higher in the Midwest we have also seen a spike in damage. 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.

Small Grains
We continue to find armyworms and cereal leaf beetles in barley and wheat fields that were not treated. Population levels remain variable throughout the state, so scouting fields will be the only way to determine if an economic level is present. In addition, with the cooler spring we are seeing extended egg laying and hatch for both insects. 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.

Seed corn maggot will be a potential problem in no-till soybeans, especially if the weather remains cool and wet. 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.

As the earliest beans emerge, be sure to watch carefully for slug damage. Remember, if you had a problem in past years, the slugs will still be present in fields and can quickly damage soybeans if they are feeding as plants emerge. You should also watch fields carefully for bean leaf beetles and grasshoppers.

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