Orchard Pollination: Honey Bees

Due to competing demands, disease, the introduction of parasitic mites (mainly Varroa destructor), and likely impacts from insecticide and fungicide use in the field, the pollination picture has changed.

Despite intense efforts to protect their bees, beekeepers are losing large numbers of colonies to mites and the diseases they transmit. In addition, since 2006, there have been additional dramatic die-offs of tens of thousands of honey bee colonies from a phenomenon known as Colony Collapse Disorder (CCD). The result has been annual losses of around 30 percent of commercial colonies, which has left many beekeepers devastated and some growers without the quantity and quality of bees needed to pollinate crops. Fortunately, the past few years have seen fewer losses attributed to CCD than at its peak between 2006 and 2014.

Healthy hives are key to maintaining high pollination activity during bloom because honey bees are vulnerable to many of the pesticides used to control insects, pathogens, and weed species. Growers dependent on honey bees must constantly maintain a delicate balance between protecting their crops from pests and pathogens and protecting pollinators. It is advisable to err on the precautionary side when using pesticides.

Recommendations for growers

• Know the pesticides you are using and their toxicity to bees (do not depend on a third party to provide this information).
• Read the label and follow the label directions.
• Never use a pesticide on a blooming crop or on blooming weeds if honey bees are present.
• The use of a pesticide pre-bloom, just before bees are brought onto a crop, is not recommended. If a pesticide must be used pre-bloom (for example, at pink in apples), select a material that has lower toxicity to bees and short residual toxicity, and apply only when bees are not foraging, preferably just after dark.
• Do not apply insecticides post-bloom (e.g., petal fall) until after the bees have been removed from the crop.
• Blooming time varies depending on cultivars. Bees pollinating one variety or crop may be at risk while another crop or variety is being treated post-bloom with insecticides. Also, while crops may have completed blooming, bees may be visiting blooming weeds in and around crops. Be aware of these situations and avoid the application of pesticides on a non-blooming crop if there is a risk of drift onto blooming crops and weeds if bees are present. If a spray must be applied, use the least toxic material and apply only when bees are not foraging.
• Protect water sources from contamination by pesticides. If necessary, provide a clean water source close to honey bee colony locations before their arrival in the orchard or crop.
• The mode of action of many fungicides in terms of toxicity to bees is unknown. Some are known to synergize with insecticides, and together these can be more toxic to bees. Avoid the application of the more toxic fungicides mancozeb and captan on blooming crops when bees are present. The use of lime sulfur during bloom has been shown to be repellent to bees for several days as well.
• For more information on toxicity, see also other resources online, such as a Northeastern IPM guide on preserving wild pollinators and several online publications at a pesticide stewardship webpage.
• Do not assume that organically approved compounds are safe for bees. More information on Organic Approved Pesticides.

As a result of high annual colony losses, fewer beekeepers are providing fewer honey bee colonies for growers and at much higher prices. In addition, the quality of honey bee colonies, at times, may be marginal for the purpose of pollination. Never before has the pollination situation been so critical. To ensure maximum crop yields, growers now must give careful attention and consideration to crop pollination.

Insecticide toxicity is generally measured using acute contact toxicity values LD50 (the exposure level that causes 50 percent of the population exposed to die).
Toxicity thresholds are generally as follows for adult bees and indicated in the table:

• Highly toxic = acute LD50 of < 2/ μg/bee
• Moderately toxic = acute LD50 of 2–10.99μg/bee
• Slightly toxic = acute LD50 of 11–100μg/bee
• Non-toxic = acute LD50 of > 100μg/bee)

Do not return managed bees to the field until after the time period when residuals remain toxic. Additional label restrictions may apply; see pesticide label.

Source: Adapted from Hooven, Sagili, and Johansen (2013), "How to Reduce Bee Poisoning from Pesticides. Pacific Northwest," Oregon State Extension Publication 591; May, Wilson, and Isaacs (2015), "Minimizing Pesticide Risk to Bees in Fruit Crops," Michigan State University Extension Bulletin E3245, and unpublished data from Biddinger, Joshi, Rajotte, Shugure, and Phan.

Source: Penn State Tree Fruit Production Guide