Seedcorn Maggot Degree Day Activity Estimates: May 27, 2021

Originally Submitted: May 27, 2021

In South Dakota, we have accumulated enough degree days across the state that the peak emergence of the overwintering seedcorn maggot population has passed. In most of South Dakota, we are at peak emergence of the second generation or slightly past it. 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. Peak emergence occurs at 360 degree days for the overwintering population, 1,080 degree days for the second generation and 1,800 degree days for the third generation.

As a reminder, the equation for degree days is:

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