by Deborah Jeanne Sergeant
What is more effective than stopping corn pests before they even start? Not much, according to Jaime Cummings, field crops and livestock IPM coordinator with Cornell University. She presented “Evaluating Seed Treatments for Seedcorn Maggot Protection in Corn: Will Neonic Alternatives Be a Good Substitute?” as part of the recent Corn Congress.
Taking place virtually this year, the Congress offered a variety of speakers addressing issues affecting corn. Cummings spoke about seedcorn maggots, wireworms, white grubs, black cutworms, slugs and armyworms.
“We’ve gotten a lot of control over these pests,” Cummings said, citing neonic seed treatments’ effectiveness with seedcorn maggots, wireworms, white grubs and black cutworm. These treatments include thiamethoxam (Cruiser), clothianidin (Poncho) and imidacloprid (Gaucho). Cummings said these controls may soon be on the chopping block in New York, however.
“There has been legislation proposed to ban some or all uses of neonics,” she said.
Though the Pollinator Risk Assessment study conducted by Dr. Scott McArt with Cornell’s Department of Entomology showed no economic benefit of widely using these seed treatments, Cummings added that little data in the study represented NY and that the studies were conducted in fields with little pest pressure.
Cummings said that seedcorn maggot activity in NY is “sporadic and highly unpredictable.” For those with loss, it can be 3,000 to 8,000 plants per acre, “which is quite significant.”
Despite some success with pest suppression, “that doesn’t mean these pests aren’t out there waiting for the ideal opportunity,” Cummings said. She thinks that many losses are not reported.
“Some organic sweet corn is transplanted specifically because of seedcorn maggot,” Cummings said.
Once the plants are well established, seedcorn maggot cannot effectively damage them. Wireworms and white grubs still cause problems for NY growers.
“We have a lot of sods and more cover crops in rotation,” Cummings said. “Those are very susceptible because that is where they like to be. A lot of the cover crop treatments are successful because of the efforts to treat these pests.”
Treating pests that do not cause economic losses wastes resources. That is why farmers should make sure neonicotinoid seed treatments actually pay off.
“We definitely know that the seedcorn maggot was one of the significant issues prior to seed corn treatments but we have little data on if they’re causing economic losses specific to New York,” Cummings said.
She added that some crops, especially soybeans, can compensate for stand losses and that most national and international research shows little to no benefit of widely adopting neonicotinoid seed treatments.
“If these seed treatments are banned, what are going to be our alternatives?” Cummings asked. She proposed that using no protection at all would equal significant losses, like that of organic growers who don’t use transplants.
In-furrow or banded insecticide treatments use older, more toxic chemicals and require more application per acre. Anthranillic diamide seed treatments are less toxic to bees, but “are we simply substituting one chemistry for another?” Cummings also pointed out that farmers are already seeing some resistance issues, plus it’s more expensive.
The Cornell IPM lab studied the effectiveness and economic sense of neonicotinoid seed treatment alternatives, like diamide seed treatments and biocontrol nematodes. The seed treatment research trials in 2019 and 2020 compared neonic and fungicide; diamide and fungicide; fungicide only; and a control among four locations that were selected for enhanced pest pressure.
“In 2019, it was extremely wet,” Cummings said. “We only got one trial in the ground and unfortunately, we didn’t have high enough pest pressure to differentiate the difference.”
In 2020, all four locations were planted on time and according to the test’s protocol, but little pest pressure made it difficult to tell the differences among the treatments.
The research indicated no clear patterns or significant yield differences across the locations. Cummings said that indicates that seedcorn maggot is an “unpredictable” pest.
“We really need to think about managing for these pests from a IPM perspective,” Cummings said. “In New York, we sometimes get out and plant when we can, dependent on the weather.”
Ontario, Canada, banned widespread use of neonics, requiring farmers to prove their need to use neonic seed treatment; however, “the burden of proof was often time-consuming or difficult,” Cummings said.
The move has caused pushback from growers and the industry. Growers have had to switch to diamides, which Cummings said does not reduce the negative effect on bees.
“We tend to complain that we don’t have as many pesticide options as other states, but up in Ontario, they have fewer,” Cummings said. “The growers had to prove the need to use the neonics.”
Further study shows that primarily, it was the use of vacuum planters that has been killing bees. Modifications to the equipment may help, but that relies upon manufacturer compliance. “We all really need to come together,” Cummings said.
That includes farmers, researchers, beekeepers, industry representatives, environmental groups, educators, regulatory agencies, legislators and policymakers.
“We need to make educated decisions based on science, not emotions,” Cummings said.