Seedcorn Maggot IPM

Seedcorn maggot damage occurs when larvae burrow into germinating seeds and consume the seed germ or when they attack the underground portions of very young seedlings. Seeds that are planted early when the weather is still cool will have the slowest rate of development and therefore will be vulnerable to seedcorn maggot attack for an extended period. In warmer weather, seeds germinate quickly, thus escaping attack. The occurrence of seedcorn maggot is typically higher when the early growing season is cold and damp. Because females use decaying organic matter as an egg laying cue, fields treated with manure or plowed to incorporate hay or cover crops into the soil are thought to be at a greater risk of attack. However, there is a dearth of data actually testing the predictors of seedcorn maggot attack and therefore researchers at Cornell are investigating the role that these cues play in mediating seedcorn maggot preference in order to provide evidence based recommendations to growers.

If seedcorn maggot damage is substantial, replanting is the only option for growers. Therefore, control methods for seedcorn maggot must be preventative.

Options for cultural control include: 

1. Delaying planting until the ground is warmer to accelerate seedling emergence.
2. Avoid planting in fields that have had manure or at least plowing in green manure and animal manure 2-3 weeks before planting to allow organic material to decompose.
3. Planting during the window of time when the first generation of flies have pupated in the soil. 

What are degree days?

Insects are cold blooded and therefore cannot develop when temperatures are below a minimum required temperature. This threshold temperature is used to calculate degree days, which are an important metric for predicting important events such as adult emergence. To estimate degree days you can simply subtract the threshold temperature from the average temperature of the day. For example, the temperature threshold for seedcorn maggot is 39℉. If on a given day the low was 40 and the high was 50, the average temperature of the day would be (40 + 50)/2 = 45℉. Now if we subtract the threshold temperature (39℉) from the average temperature (45℉), we find that 6 degree days accumulated on this day. A modeling approach can account for finer scale variation in temperature throughout the day to allow for a more accurate estimate of degree days. For the overwintering generation of seedcorn maggot, it is estimated that peak emergence occurs at 360 accumulated degree days.