Stalk borer: Management decisions

Targeting stalk borer egg hatch outside of corn is a method of control, but it most beneficial in areas with constant pressure. Apply to surrounding grasses at 570-750 degree days (base 41). But spraying at this point is a guess because there is no way to know how many eggs are out there and how many survived the winter. Spraying too early is a waste of money because the residual will not be effective when the larvae do hatch.

The second, preferred alternative is to target insecticides while larvae are moving to adjacent corn. Larvae begin to move at 1100 degree days and 50% of larvae are moving at 1650 degree days. Start to scout for infested plants at 10% migration.

The larvae are not highly mobile, and typically only move into the first four to six rows of corn. Examine 20 ears in 5-6 locations near likely areas of damage. Look for new leaves with irregular feeding holes or for small larvae resting inside the corn whorls. Larvae will excrete a considerable amount of frass pellets in the whorl or at the entry hole in the stalk. Exposed larvae can be killed with a foliar insecticide treatment, but tunneling larvae are not susceptible. Young corn is particularly vulnerable to severe damage, but plants are unlikely to be killed once reaching V7 (seven true leaves).