Judicious Soybean Protection

March 5, 2016 02:12 AM
 
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Researchers urge more careful use of neonicotinoid seed treatments

Neonicotinoid seed treatments have widespread use, but their benefit is primarily “targeted, high-risk situations” in Midwestern soybean fields.

According to “The Effectiveness of Neonicotinoid Seed Treatments in Soybean,” a joint publication from 12 Midwestern universities, soybean farmers are overusing neonicotinoid seed treatments in soybeans.

The researchers note neonicotinoid seed treatments offer young soybean plants a three-week window of protection after planting, which makes them quite useful for managing early season pests. However, the treatments’ usefulness is primarily confined to “targeted, high-risk situations,” such as:

  • Fields recently converted from CRP or grassland to soybeans.
  • Fields with animal manure, green cover crops or numerous weeds.
  • Double-crop or specialty (food-grade or seed) soybean fields.

Other high-risk scenarios in soybeans are relatively uncommon in the Midwest. For example, wireworms, white grubs and seedcorn maggots don’t often reach economically damaging levels. Adult bean leaf beetles tend to cause only cosmetic damage in newly emerged soybeans.

Unfortunately, seed treatments have little value controlling one of the biggest soybean pests—the soybean aphid. Neonicotinoid seed treatments are labeled for soybean aphid, but thresholds usually occur midsummer, or weeks after the seed treatments’ window of protection has ended. Meanwhile, natural predators, such as Asian lady beetle and parasitic wasps, often suppress earlier season infestations of soybean aphid.

Medical patients expect to know why a doctor wrote a specific prescription. Farmers should have the same expectation of insecticidal seed treatments, says Chris DiFonzo, field crops entomologist, Michigan State University.

“Why shouldn’t we be equally as curious about the insecticides we use?” she says. “Insecticidal seed treatments control only a few types of insects well, and for only a short time after planting. I am not saying neonic seed treatments aren’t justified—they just are not justified as often as they are used in soybeans.

“I recognize it might not be easy to get seed treated with fungicide only, for example,” DiFonzo adds. “Many dealers offer only combo products or only guarantee seed treated with a full package of insecticide and fungicide. If growers want more choice in seed treatment in the future, they have to speak up and be persistent.”

The report also lists several risks of neonicotinoid seed treatments, including toxicity to bees and other pollinators. The Environmental Protection Agency (EPA) is in the midst of risk-assessment reviews for all major neonicotinoids, including imidacloprid, clothianidin and thiamethoxam. 

According to a Bayer response to the EPA report: “[Neonicotinoids] have been widely adopted by growers because of their favorable human and environmental safety profile, especially when compared to the older products they replaced. Neonics are critically important to today’s integrated pest management programs, allowing farmers to manage destructive pests, preserve beneficial insects and protect against insect resistance.”

Researchers in the 12-university report recommend an integrated insect pest management plan, including crop rotation, conservation of natural enemies, planting pest-resistant varieties, scouting and applying insecticides at established thresholds.  

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