Unlike its name denotes, seedcorn maggot (Delia platura) attacks more than just corn seeds. It also affects legumes, cucurbits and more.
Knowing when and where seedcorn maggot (SCM) will emerge can help producers combat it more effectively, especially in light of the DEC’s prohibition on treated seeds coming in 2029. Signed in December 2024, the law bans using neonicotinoid (neonic) pesticide-treated seeds for corn, soybean or wheat without a waiver.
Chloe Yi-Luo Cho, a Ph.D. candidate in the Poveda Lab in the Department of Entomology at Cornell University, presented her research project on SCM at the recent Soybean & Small Grains Congress. Cho is currently in year three of a four-year research project studying how farmers can predict SCM emergence. If farmers can prove they’re at elevated risk using an assessment, she hopes that they may be eligible for a waiver to use neonic-treated seeds. Her work involves developing such an assessment tool.
SCMs feed on decaying plant and animal material, including seeds farmers have planted. The larvae attack seeds before and during germination, causing patchy and sporadic loss.
“There’s nothing you can do once SCM have decimated the seed,” Cho said.
Prevention is key. Cho’s preliminary findings are trying to answer the questions “Can we predict when and where SCM will emerge and cause damage in New York State?” and “Do local management practices exacerbate SCM infestation?”
Because every insect species requires a certain amount of heat to develop, Cho thought it helpful to track temperatures to identify SCM’s ideal range for emergence in New York. Since SCM flies emerge much earlier than predicted, she believes a new tool is needed. Previous models were for other parts of the U.S. and Canada.
In New York, emergence occurs between 39º and 84º F.
In 2022, 79 sites participated in Cho’s SCM risk assessment tool study, followed by 54 in 2023 and 40 in 2024. She asked growers to record field information in an online risk assessment tool. This included measurement of SCM damage and populations.
Cho had growers place sticky cards outside weekly to help capture and estimate adult numbers. She and fellow researchers also buried wire mesh traps baited with lima bean for two weeks, which she said SCM finds very attractive, along with soybean and corn seeds.
Chloe Yi-Luo Cho, a Ph.D. candidate at Cornell University, presented her research project on seedcorn maggot. Photo by Deborah J. Sergeant
“We caught very few maggots using corn and soy,” Cho said. “Lima bean is used to get non-zero data so we can compare treatments.”
Capturing adults did not prove a useful measure of how many maggots were present. “We found hundreds of adults and still have zero maggots on the seeds,” Cho said.
She also learned that larvae and seed damage are both low and sporadic. While disappointing for a researcher, it is important for farmers to know that they have time to develop a defense against SCM once it hits their farms.
Cho further wanted to learn if local management practices exacerbate SCM infestation, such as soil amendments, cover crops and insecticides and the use of insecticide-coated seeds.
“We found no evidence that the addition of manure or plant material increases SCM damage in corn or beans,” Cho said. “There’s no significant percent in amount of seeds damaged across the four treatments.”
The treatments were alfalfa; manure; a mixture of manure and alfalfa; and nitrogen, phosphorus, and potassium fertilizer.
“We found no evidence that the addition of manure in any form increases SCM abundance,” Cho said. “Maggot abundance depends more on the crop and seed type rather than any sort of organic matter.”
In field trials among 25 sites over two years with a rye cover crop or a wheat cover crop, the plots showed no difference if corn seeds or lima bean seeds had a cover or not as far as presence of SCM.
“Cover crops did not increase SCM pressure,” Cho said. “Insecticide and fungicide-only seed treatments perform similarly to each other, even in the presence of cover crops. The 2025 experiment will expand upon this study.”
She reassured farmers concerned about SCM that their larvae presence is still sporadic and low. “Even when adults are abundant, seed damage is low,” she said. “It doesn’t mean there’s a higher risk of damage. Drivers of adult abundance are not driving larvae abundance and risk. Upcoming experiments will focus on larvae collection and local management practices.”
Cho encourages anyone who is farming field corn, soybeans, sweet corn or snap beans and who is interested in participating in the study to contact Mike Stanyard or Mike Hunter with Cornell. Farmers will need to commit for three growing seasons and will receive seeds and compensation. They will need to plant, manage normally and harvest.
CCE’s Northwest Dairy, Livestock & Field Crops Program hosts the Soybean & Small Grains Congress annually.
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