Seedcorn Maggot Degree Day Activity Estimates: May 20, 2021

Originally Submitted: May 20, 2021

Seedcorn maggots can be an early-season pest of corn and soybean in South Dakota, typically affecting 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. In South Dakota, we have accumulated enough degree days across the state that the peak emergence of the overwintering population has passed. In areas around Winner and Vermillion, we are approaching the peak emergence of the second generation. 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 degrees Fahrenheit and an upper developmental threshold of 84 degrees Fahrenheit. The peak emergence for the overwintering population occurs at 360 degree days. The peak emergence for the second generation occurs at 1,080 degree days. The peak emergence for the third generation occurs at 1,800 degree days.

As a reminder, the equation for degree days is:

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