By Andrew Porterfield
The class of insecticides called neonicotinoids (neonics) were introduced to a lot of fanfare from farmers and environmentalists alike. They were seen as far less toxic than alternative pesticides, and could be applied into the soil or on seeds, avoiding the damage to beneficial insects that’s often caused by sprays.
But recently, a number of environmental groups and scientists have expressed concern over neonics and their possible impact on honey bees, and the U.S. Environmental Protection Agency has questioned whether or not there is any economic benefit to applying neonics to certain crops as a seed treatment.
In 2014, the EPA issued a report stating that soybean growers who use seeds that were treated with neonics before planting did not experience any economic benefit from the practice. Showing economic benefit is an important part of integrated pest management, so not having any advantage demonstrated that IPM-practicing farmers may be wasting their money, and not following good IPM practices.
However, the EPA came under harsh criticism for its report, including responses from the U.S. Department of Agriculture and the American Soybean Association. Also, scientists from Mississippi State University discovered that pest pressure played a strong role in establishing an economic threshold for using neonics, at least on rice.
The same scientists, led by Jeff Gore, an extension/research professor at Mississippi State, recently evaluated 170 field trials on soybean fields in four southern states (Arkansas, Louisiana, Mississippi, and Tennessee) over 10 years. Their meta-analysis appears in the Journal of Economic Entomology.
Gore and his colleagues discovered that treating soybean seeds with neonics (imidacloprid or thiamethoxam) and a fungicide provided higher yields than seed treatments using a fungicide only. Such treatments resulted in yields that were 203 kg/hectare higher in Louisiana, 165 kg/hectare higher in Mississippi, 112 kg/hectare higher in Arkansas, and 70 kg/hectare higher in Tennessee. Economic returns for neonic seed treatments were higher in four out of the 10 years studied. The higher yields in Louisiana and Mississippi were great enough to constitute an economic benefit for IPM practices.
In the southern U.S., soybean planting has changed, and farmers have begun planting earlier in the year. This change avoids problems with drought conditions and excessive heat, but also introduces infestation of early-season pests, such as bean leaf beetles, white grubs, wireworms, lesser cornstalk borers, three corner-alfalfa hoppers, grape colaspis, pea leaf weevils, and many species of thrips. Neonicotinoid treatments have effectively controlled these early-season pests, and are the most widely used pesticide on soybean. Neonics are also used on row crops such as rice, corn, and cotton. They are valued for their ability to protect against insects that suck sap from plant leaves and stems.
The article notes that other studies (including the EPA’s) were somewhat skewed toward farms in the northeastern or north Midwestern states in the U.S., which have lower pest pressures than farms in the lower Mississippi Valley.
“We believe that the neonicotinoid seed treatments did provide a benefit to growers in our area and that the EPA document did not represent our region of the U.S.,” said Dr. Gore. “The data do contradict the EPA document to some degree.”
However, he noted that the average yield improvements, while statistically significant, were not dramatic (about two bushels per acre measuring using the English system). He predicts that many scientists may argue that these benefits were not high enough to cross the economic threshold important to IPM. But, Gore said, “If growers were using some other practice that caused them a two-bushel-per-acre loss or they had significant economic loss in four out of 10 years, no one would argue that this was a bad practice.”
Since the opposite indeed was observed, the scientists argue that enough instances of higher yield made neonic seed treatment a beneficial practice.
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Andrew Porterfield is a writer, editor and communications consultant for academic institutions, companies and non-profits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield on Twitter, or visit his Facebook page.