Seedcorn Maggot Degree Day Activity Estimates: April 29, 2022

Written with contributions by Shelby Pritchard, former SDSU Extension Pest Management Specialist.

Originally Submitted: April 29, 2022

Seedcorn maggots can be an early-season pest of corn and soybean in South Dakota. Typically, seedcorn maggots affect crops that are emerging or have recently emerged. Seedcorn maggots can cause direct loss by destroying planted seeds. They can also reduce stands by feeding on the growing point of the plant. For most of South Dakota, we have accumulated enough degree days across the state that the peak emergence of the overwintering population has passed (Table 1). Seedcorn maggot management must be done before planting, or the populations can be avoided by not planting during times of peak emergence.

Predicting Seedcorn Maggot Emergence Activity With Degree Days

The emergence of seedcorn maggot flies can be estimated by using degree days with a lower developmental threshold of 39°F and an upper developmental threshold of 84°F. The peak emergence for the overwintering population occurs at 360 degree days. The peak emergence for the second generation occurs at 1080 degree days. The peak emergence for the third generation occurs at 1800 degree days (Table 2).

As a reminder, the equation for degree days is:

(Maximum Daily Temperature + Minimum Daily Temperature) ÷ 2 - The Developmental Threshold