The seedcorn maggot is the larval form of a tiny fly. Though the adult fly is not much of a threat, the maggot punches well above its weight, causing considerable damage to newly planted corn and emerging seedlings. In 2024, seedcorn maggot caused estimated yield losses of 858,000 bushels in corn and 138,000 bushels in soybeans across the U.S.¹,²
What does seedcorn maggot look like?
- Larval stage: small, off-white or yellow-white, legless, tapered body about 6 mm long
- Maggot pupa: smaller than the maggot, brown to dark brown and capsule-shaped
- Adult fly: around 5 mm long, brown-gray, with gray stripes on the male’s thorax
Seedcorn maggot life cycle
The seedcorn maggot overwinters in the soil as a pupa. It emerges as an adult once sufficient growing degree days (GDD) have accumulated, typically around May in much of the Midwest. Multiple generations of seedcorn maggot can pop up throughout your growing season, but first generation seedcorn maggot typically have the largest impact, since their emergence typically occurs from April to June, just in time to munch on seeds and new seedlings.
How does seedcorn maggot damage crops?
The maggots burrow into corn seeds and emerging cotyledons to feed, often ruining seeds, preventing germination and emergence, and causing poor stand establishment. They sometimes feed on seedling stems, leading to weak or stunted young corn plants at risk for premature death. Cool and damp conditions slow germination and give the maggots more time to feed.
How to identify seedcorn maggot
About a week after corn emergence, scout fields for stand loss. Where stand loss is evident, dig around a bit under the row skips to look for maggots and pupae and their tell-tale signs:
- Seeds that are broken open, hollowed out or otherwise damaged
- Underdeveloped seedlings
How to prevent seedcorn maggot infestation
If seedcorn maggots are into your seeds, there is no rescue treatment. Proactive management is critical.
Before planting
Adult female seedcorn maggots prefer to lay eggs in recently turned cover crops or freshly manured fields, so allowing two weeks between tilling or manure application and planting can buy you time by providing more GDD for seedcorn maggots to develop and, with luck, be out of the larval stage and into the pupal stage before your seeds are in the ground. This prime period for planting to avoid seedcorn maggot is sometimes called the pupation or “fly-free” period.
When should you plant?
Arriving at that “fly-free” period for your locale involves keying off the seedcorn maggot’s growing degree days (GDD) numbers in your area. For more detail about your local growing degree days (for seedcorn maggot and other pests), visit Iowa State University’s Pest Map & Forecasting app, which can provide a GDD figure for each year’s “fly-free” period in your location and help guide planting.
Treatments and prevention at planting time for seedcorn maggot control
Since rescue treatment won’t help with an existing seedcorn maggot infestation, steps to prevent the pest must be taken at planting time, whether through seed treatments, in-furrow insecticides or a combination.
Poncho®Votivo® seed treatment for corn seed and Poncho® Votivo® Precise for soybean seed helps plants get off to a great start in that critical, early-season growing period when plants are most vulnerable. It provides broad spectrum early-season insect control on key corn pests, including seedcorn maggot, by creating a living barrier that grows with the roots, also protecting against other key pests like nematodes.
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.
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Endnotes
- “Corn Invertebrate Loss Estimates from the United States - 2024.” Crop Protection Network, 17 Feb. 2025, cropprotectionnetwork.org/publications/corn-invertebrate-loss-estimates-from-the-united-states-and-ontario-canada-2024. Accessed 27 Feb. 2026.
- “Soybean Invertebrate Loss Estimates from the United States - 2024.” Crop Protection Network, 3 Sept. 2025, cropprotectionnetwork.org/publications/soybean-invertebrate-loss-estimates-from-the-united-states-2024. Accessed 27 Feb. 2026.
