Minimizing pesticide exposure to bees in fruit crops
Use these practices and guidelines for minimizing exposure of bees to pesticides while still managing pests and disease in fruit crops.
Most fruit crops grown in Michigan need bees, whether managed or wild, for pollination. Honey bees are by far the most important crop pollinators because they are abundant, will collect nectar and pollen at distances up to five miles away from their hive, and are relatively easy to transport in and out of plantings in time for bloom. Honey bees are typically placed in the field when crops are at 5-10 percent bloom and then removed at “petal fall.” While bees are essential for the production of most fruit crops, pest management is also critical for producing marketable and profitable yields. This can create a potential conflict between the need to protect bees and the need to prevent insect and disease pests.
The challenge for commercial fruit growers is to manage the pests and diseases that cause crop losses while minimizing pesticide exposure to bees across the variety of crops and cultivars that may bloom at different times throughout the spring across the farm. Many insecticides are known to be acutely toxic to bees and are restricted from use during bloom to minimize exposure. Newer research suggests that other insecticides, some fungicides, and inert ingredients in pesticide formulations may affect brood development when residues are brought back to beehives. As part of the response to increasing concerns and more detailed information about pesticide effects on bees, there have been recent changes to pesticide labels and the re-evaluation of practices that will minimize pesticide exposure to bees in fruit crops.
Michigan State University Extension has provided guidelines for fruit growers on minimizing the risk of pesticides to bees. It all starts with good communication between growers and their beekeepers. Discussions during the winter can set the stage for how many hives will be needed and when and where to put the bees on the farm. As the season starts, making good pre-bloom decisions and avoiding exposure of bees to toxic pesticides are essential.
Some general practices that can minimize this risk include:
- Draft a written contract with the beekeeper to clarify expectations on both sides.
- Select a location for hives on the farm that is upwind from potential drift.
- Honey bees can cover a lot of ground, so place hives in safe locations rather than along drive lanes within or close to the planting.
- Know when to expect the delivery of hives and when they will be removed.
- In the company of the beekeeper, examine delivered hives to know the health and strength of the hives you are renting.
- At all times, follow the label for pesticide application. New labels for neonicotinoids and for Exirel have bee-specific language.
Specific practices to minimize exposure of bees to pesticides include:
- Provide sufficient time between pre-bloom sprays and placement of hives to avoid exposing bees to lethal residues.
- Do not apply bee-toxic insecticides until crop flowering is complete and all petals have fallen.
- Do not apply insecticides permitted for use during crop bloom while bees are foraging. Spraying after sunset can greatly reduce the risk of exposure.
- Select less toxic insecticides whenever possible. Consult the Michigan Fruit Management Guide E-154 for the table of insecticide toxicity ratings for honey bees.
- If fungicides are needed during bloom, spray after sunset or when air temperature is below 55 degrees Fahrenheit whenever possible.
- Turn off the sprayer near hives and avoid pesticide drift onto open flowers.
- Use selective herbicides to eliminate forbs from drive lanes or mow before spraying to reduce flowering weeds in the crop field.
- After crop bloom, draw wild bees away from crop plantings by providing non-crop flowering plants elsewhere on the farm (i.e., meadows that contain bee-attractive plants or summer flowering cover crops like buckwheat).
For more detailed information on this topic, consult the recently updated Oregon State University publication “How to Reduce Bee Poisoning from Pesticides.”
Drs. Gut and Isaacs' work is funded in part by MSU's AgBioResearch.