Western Bean Cutworm eggs have been found Northwest of Fowler in a corn field. This insect is an occasional problem in Western Kansas. Careful scouting and timing of sprays are necessary to obtain adequate control.
The larvae feed on the reproductive parts of the plant – tassels, pollen, silks, and developing ears in corn and flowers, leaves and developing pods in dry beans. Infestations can cause considerable losses in both quantity and quality of the crop produced. Damage from the larval feeding can also lead to secondary fungal infections in corn ears and can open up pods to pathogens and other insects in dry beans.
Field scouting should begin at the first sign of tasseling and continue until the silks turn brown. Look for round, white eggs in groups of 5 to 200 on the upper surface of the upper leaves near the whorl. The eggs will gradually become darker in coloration, hatching in five to seven days. Newly hatched larvae are pale with light-brown stripes running lengthwise down the back.
In dry beans, eggs are laid on the underside of bean leaves deep within the canopy, making them difficult to find.
An average of eight plants with eggs or small larvae per 100 plants (when the corn is 95 percent tasseled) justifies control measures. This application timing increases the chance that the worms will be feeding on the new pollen and they will be exposed to the insecticide, resulting in a much better control. Chemigation has also provided a very good control at the lowest rates. Control will be reduced if applications are delayed until all silks have emerged or if larvae have already entered the ear tips.
Some of the new Bt corn hyprids have some resistance, so take this into account when selecting hybrid seed. Bt corn with Herculex I (Event TC 1507 with Cry1F) provides protection against western bean cutworm larvae and may be a consideration for producers who have experienced problems with this pest. Check out Texas A&M’s Bt Trait Table to see what proteins they express and the pest it targets.
Please refer to the Corn Insect Management Guide for treatment options on Western Bean Cutworm on page 15. The University of Nebraska also has a great website for more information on Western Bean Cutworm including a short introduction, biology and behavior.
