Neonicotinoid insecticide update
Getting a jump on pests can help improve your chances warding off a major infestation. Chloe Yi-Luo Cho, Ph.D. candidate in entomology at Cornell, presented “Early-Season Pest Damage Across New York: Risk Under Different Management Practices in Light of the Neonicotinoid Ban” at the recent Soybean & Small Grains Congress, hosted by CCE’s Northwest New York Dairy, Livestock & Field Crops Program.
A group of insecticides designated as 4A by Insecticide Resistance Action Committee, neonicotinoid insecticides (neonics) are systemic, absorbed by the plant tissue before moving through the vascular system. As highly water-soluble substances, these are taken up by the plant when applied to the soil. As the most widely used insecticides available, neonics target a range of important insect pests. They include acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid and thiamethoxam.
The majority of corn and soybean seeds in the U.S. are treated with neonics as a preventative treatment against pests like seedcorn maggot, wireworms, white grubs and corn rootworm. Cho said this group of treated seeds is controversial because of the limited evidence of economic benefits and the environmental risk to non-target species.
One to two percent of neonics applied to corn and soybean seeds are taken up by the plant; 5% to 10% are lost as dust at planting; and 85% or more goes elsewhere. Cho said the EPA concludes that these seed treatments make no difference in yield.
In June 2020, a state-funded report that provided a risk-benefit analysis of neonicotinoid insecticide use in New York State in agronomic and specialty crops was published, Cho said. The study focused on where there are risks to pollinators, the economic benefits to users and when there are viable replacements. The report found there are some seed treatments in field crops providing the highest risk to pollinators in New York.
New York’s Birds & Bees Protection Act in 2023 was the first prohibiting use of neonics in seed coatings beginning Jan. 1, 2029, unless a waiver is issued by the state’s Department of Environmental Conservation.
“There’s a series of things you can go through to get a waiver,” Cho said. This might include a farmer with a field that is high risk.
To obtain a waiver, farmers need to complete a pest risk assessment, undergo IPM training, limit seed use to approved properties and maintain accurate records. The IPM training must be documented and up to date. It’s also important to maintain accurate pest risk assessment records and document where seeds are planted.
In light of the Birds & Bees Protection Act, Cho said to look at early-season pets that pose the greatest risk to field crops, along with actively monitoring pest populations and damage.
“Can we predict where and when early-season damage will occur?” Cho asked. “How high is the damage caused by early-season pests? To what extent is pest pressure shaped by local management practices?”
The main early season pest in New York is the seedcorn maggot. It feeds on decaying plant and animal material, including seeds, and is considered a pest of corn, legumes, cucurbits and other plants. The larvae feed on seeds before and during germination, especially in cool, damp conditions, resulting in patchy and sporadic stand loss.
“By the time you notice damage, the seeds are dead,” Cho said.
In her 2022 study, Cho monitored the abundance of adult seedcorn maggot using blue and yellow sticky cards. “By far and away, the blue sticky cards were more effective,” she noted.
Adding the P-316 lure, which is commercially available, increased the attractiveness of the sticky cards.
Cho found that seedcorn maggot adults are present from April through November and emerge first before planting. Unfortunately, there’s no association between adult abundance and maggot abundance.
From now through 2027, Cho is undertaking a largescale, long-term experiment sampling at 56 farms growing field corn, soybeans, sweet corn and snap beans using neonicotinoid- and fungicide-treated seeds and fungicide-only treated seeds. The fungicides used are azoxystrobin, fludioxonil, mefenoxam, thiabendazole, sedaxane and picarbutrazox. The neonic seeds will have thiamethoxam.
The results so far show fairly low pest abundance with no significant difference between treated and untreated seeds.
“Last season was a worst-case scenario for driving seedcorn maggot,” Cho said, but their numbers were still low.
In the preliminary results, “it seems we can conclude that neonicotinoid seed treatment reduces the abundance of early-season seedcorn maggot in soybeans. Seedcorn maggot pressure is still fairly low at six maggots per 100 seeds. Neonicotinoid seed treatment does not provide a benefit in terms of stand counts or yield. There doesn’t seem to be a cost in removing neonicotinoid seed treatments in terms of stand loss, biomass and yield for field crops. However, we could not capture damage rates for early plantings and require more data.”
Adult abundance of seedcorn maggot relies upon weekly temperature, rainfall, soil characteristics, percent of corn vs. natural habitats and management practices like cover crops and manure. The lattermost interventions appear to increase adult abundance, but that does not translate to crop damage. Cold, wetter weather earlier in the season tends to drive abundance but not damage.
“Neither cover crops nor manure applications appear to exacerbate seedcorn maggot damage in corn,” Cho said. “Preliminary recommendations are that it is safe to continue using manure and cover crops in field crops regardless of the seed treatments.”
