Forecasts for planting timing and seed corn maggot in 2023

Anthony Hanson, Extension Educator - Field Crops Integrated Pest Management (hans4022@umn.edu)

Figure 1. Seed corn maggot feeding on a soybean cotyledon.

Overlap between how temperatures affect planting timing and pest development frequently affects management decisions, and that is beginning to show in our shift from a cool spring to warm temperatures in May. Warm temperatures usually mean field work and planting progresses quickly, but warm weather can also speed up the timing of insect emergence.

Seed corn maggot (SCM) feeds on seed and newly emerging seedlings where adult females lay eggs in disturbed soil beginning in spring. Eggs can hatch within two to four days and maggots move to and feed on seed and germinating plants. Multiple generations continue throughout the growing season in fairly distinct waves for each generation. Like with other insects, the warmer the average daily temperature, the quicker SCM develops and progresses through each generation as populations build.

Infestations are most common in cool wet springs and areas with high organic matter (e.g, manure or recently incorporated plant material). Corn and soybeans are the most economically affected crops (Fig. 1), but seed corn maggot has a wide host range on various agronomic and horticultural crops.

To predict pest risk, two questions need to be answered:

• When will the pest show up?
• Will the pest have sufficient population size to cause significant damage?

Predicting damage timing

The timing of damage occurs in fields planted during the adult population peak for each generation, which can be predicted by calculating degree-days specific to seed corn maggot.

As of May 8, 2023, the overwintering generation peak emergence at 360 degree-days is occurring in along the Iowa border and is forecast to move up to central Minnesota within the next week as daily temperatures increase to the 70s and 80s °F for highs along with lows above 50°F. (Figs. 2 and 3, click to view full-size images).

Figure 2. Current SCM degree-days as of May 8, 2023.

Figure 3. Forecast SCM degree-days for May 14, 2023.

Degree-day maps only indicate the time of year when high risk can occur and do not guarantee the seed corn maggot peak population will be large enough to cause economic damage.

As of May 7, current USDA planting estimates for the state are 38% for corn and 13% for soybeans. This year, the timing of the peak first generation will probably be occurring after much of the corn goes in the ground this week across southern and central Minnesota, though corn or soybeans planted closer to the weekend of the 14th could be at higher risk if a field has other risk factors that make SCM problems more likely. 

Risk of high populations and management

For seed corn maggot, answering if it will be at damaging population levels is less exact than predicting timing. Fields with historical seed corn maggot problems or high organic matter should be considered for additional management if they are being planted in the coming week. Fields with cover crops recently incorporated or tilled under can be more attractive to SCM, but fields using no-till practices, regardless of cover crop adoption, tend not to have increased populations.

Planting can instead be delayed in these high-risk fields until after peak seed corn maggot flight; this decision also needs to be balanced with the likelihood of seed corn maggot reaching damaging levels in particular field and if it’s economically feasible to wait another week depending on the growing needs of the crop. At current temperature trends, we should be past peak by the middle of next week depending on where you are located in the state. Forecast maps for SCM are updated twice a week if you want to follow updated forecasts through the planting season.

After planting, there are no effective treatments once damage occurs, though there are some insecticides labeled for in-furrow or seed-applied use at planting. Insecticide seed treatments can be effective protection, but are best used when you know a field is in a high-risk situation. Using a seed treatment as a preventative in low-risk fields without a history of SCM isn't likely to give a return on investment. 

For more information

Continued updates on seed corn maggot and other pest forecasts are available at: https://z.umn.edu/pestforecast

For management of seed corn maggot in soybean, visit:
https://extension.umn.edu/soybean-pest-management/seedcorn-maggot