MINNEAPOLIS — The challenges posed by soybean aphid resistance to pyrethroid insecticides have resulted in more growers turning to insecticides containing chlorpyrifos for management of soybean aphid outbreaks. Chlorpyrifos is an organophosphate insecticide with broad-spectrum activity that is used for management of pests in various agricultural crops. Chlorpyrifos is an active ingredient in various products, including but not limited to Lorsban, Cobalt, Dursban, Nufos and Yuma. In this article, we urge growers and applicators to keep in mind best management practices (BMPs) for use of chlorpyrifos and provide a reminder about respirator requirements for this insecticide.

Best Management Practices: In 2012, the Minnesota Department of Agriculture (MDA) determined chlorpyrifos to be a “surface water pesticide of concern,” due to frequency and magnitude of detections of this insecticide in surface waters of Minnesota. Consequently, MDA developed best management practices (BMPs) for use of chlorpyrifos. The BMPs help users follow mandatory label requirements and provide integrated pest management (IPM) recommendations to reduce insecticide input. Label use requirements and setbacks are legally enforceable. Recommendations not included on insecticide labels are voluntary.

Some key points from the BMPs for chlorpyrifos are:

• Apply product according to label
• Maintain legally required application setbacks from permanent water bodies (check individual labels)
  • Ground boom: 25 ft
  • Orchard airblast: 50 ft
  • Aerial (plane/helicopter): 150 ft
• Apply large droplets when possible
• Utilize integrated pest management (IPM)
• Rotate insecticides
• Manage and dispose of unused product properly

Recently, detections of chlorpyrifos in water bodies have been increasing. If the BMPs prove ineffective at decreasing detections of chlorpyrifos in surface waters, mandatory restrictions on use and practices may be required by MDA.

Respirators: Labels of chlorpyrifos-containing insecticides indicate that respirators are required. Please pay careful attention to specifications for respirator type listed on the label. Most chlorpyrifos-containing pesticides require a respirator with an R or P filter, indicating that the respiratory hazard is oil-based.

Note that the Environmental Protection Agency’s (EPA’s) Worker Protection Standards mandate that a medical evaluation and fit test be performed prior to wearing respirators that are required by pesticide labels. For individuals working as commercial applicators, see your coop’s health and safety manager for a fit test. For farmers, this map shows locations offering fit testing across the state.

Cholinesterase testing: Exposure to organophosphate insecticides (including chlorpyrifos) can lead to cholinesterase inhibition. Cholinersterase is an enzyme that is required for proper function of the nervous system in humans. Reductions in cholinesterase can lead to twitching, paralyzed breathing, convulsions, and in extreme cases death. For individuals applying organophosphates for more than a total of 30 hours in 30 consecutive days, OSHA recommends obtaining a baseline cholinesterase test prior to use, as well as a test each time an applicator reaches 30 hours of exposure. If you observe a 30% reduction in cholinesterase activity or a 40% reduction of plasma cholinesterase activity, stop using organophosphate insecticides immediately. OSHA considers it safe to return to work when cholinesterase levels return to 80% of the baseline.

— Robert Koch (Extension Entomologist, Univ. of MN), Trisha Leaf (Research Scientist, MN Dept. of Agric.), and Natalie Hoidal (Pesticide Safety & Environmental Education, Univ. of MN)

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