orchard in bloom

Jun 7, 2022
Reducing pesticide risk to bees during fruit crop bloom

Honey bee and bumble bee colonies are being delivered to farms, and wild bees are becoming active during the warm spring weather. These and other flower-visiting pollinators should be protected by minimizing pesticide exposure and risk, so they can continue to provide pollination and contribute to high quality and abundant yields. Delaying spraying until bloom is over is the best way to prevent risk, but if there are economic levels of insect pests or conditions for pathogen infection growers may need to spray to protect the crop. If this happens, select pesticides that are 1) allowed for use during bloom, and 2) have the lowest toxicity to bees.

Michigan State University Extension documents can help with these decisions, including the guide to minimizing pesticide risk in fruit crops. This covers a lot of what is known about pesticide risk, although many aspects are still not well understood including how mixtures affect bees and how native bees are affected by these chemicals.

There is also an excellent online resource for the latest information on pesticide risk to bees, available from the University of California Integrated Pest Management Program. Here you can search for any trade name or active ingredient to find information on effects on adult bees and on their larvae (or brood).

For apple growers, USApple has partnered with the Honey Bee Health Coalition to develop some best management practices with input from IPM specialists, growers, and beekeepers. The guide is available here: Apple Best Management Practices.

For Michigan blueberry growers, MSU Extension developed a pollinator stewardship guide has with input from the Michigan Blueberry Commission, and is available here: Blueberry Pollinator Stewardship Guide.

Many of the guidelines in these documents apply across all fruit crops, and include the following key points:

  • Use integrated pest management (IPM) strategies to reduce pesticide exposure to bees.
  • Minimize the use of insecticides and fungicides during bloom.
  • Apply when bees are not actively foraging and when conditions are unlikely to cause drift.
  • Calibrate or modify sprayers so that applications go where they are intended.
  • Support bee health by establishing flowering plants, bushes, and trees on your farm.
  • Communicate with your beekeeper about pesticide application plans.

Consider pesticide formulations

Although it is not registered for use during bloom, the recent registration of Endigo ZC has brought up some questions about formulations in relation to pesticide risk to bees. Encapsulated pesticides are the most likely to be collected by foraging bees because the tiny spheres are collected by the charged hairs on bees’ body. Powder formulations are also more likely to be picked up from plant surfaces than liquid formulations so keep this in mind when selecting between two similar insecticides with different formulations.

Consider bee foraging ranges

Honey bees and bumble bees will fly to non-crop flowers on your farm to forage plus they can fly over a few miles to reach rewarding flowers. Because of this it is important to minimize drift onto adjacent flowering plants near crops. Also, consider nearby bee colonies that may still be actively visiting your farm even if your crop has finished bloom. Mowing flowers off attractive ground covers within the crop area can help reduce exposures, as well as making applications when bees aren’t actively foraging.

– Rufus Isaacs and Julianna Wilson, Michigan State University Extension

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