Orchard IPM - Protecting 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.

CCD is under investigation and pesticide exposure is one of several contributing factors being studied. Pesticides under investigation include those used within the hive for mite and disease control as well as those used on crops that may inadvertently find their way into hives. 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. Until we have more documented information, 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 prebloom, just before bees are brought onto a crop, is not recommended. If a pesticide must be used prebloom (for example, at pink in apples), select a material that has a lower toxicity to bees and a short residual toxicity, and apply only when bees are not foraging, preferably just after dark.
• Do not apply insecticides postbloom (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 postbloom 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 nonblooming crop if there is 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 source of water close to honey bee colony locations prior to 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 and 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 to bees.

As a result of mites, diseases, and CCD, 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.

Adapted from Riedl, H., E. Johansen, L. Brewer, and J. Barbour, How to Reduce Bee Poisoning from Pesticides (Pacific Northwest Extension, 2006), with local recommendations added based on:

• Biddinger, D. J., J. Robertson, C. Mullin, J. Frazier, N. Joshi, M. Vaughn, and S. Ashcraft. 2013. Comparative toxicities and synergism of orchard pesticides to Apis mellifera (L.) and Osmia cornifrons (Radoszkowski). PloS One 8(9): e72587. doi:10.1371/journal.pone.0072587.
• Hopwood, J., M. Vaughn, M. Shepherd, D. Biddinger, E. Mader, S. Black, and C. Mazzacano. 2012. Are Neonicotinoids Killing Bees? A Review of Research into the Effects of Neonicotinoid Insecticides on Bees with Recommendations for Action. The Xerces Society for Invertebrate Conservation, Portland, OR. 44p.
• Park, M., B. Danforth, J. Losey, D. Biddinger, M. Vaughn, Jolie Dollar, E. Rajotte, & A. Agnello. 2012. Wild Pollinators of Eastern Apple Orchards and How to Conserve Them. Cornell University, Penn State University, and The Xerces Society for Invertebrate Conservation. 19 p.

*These materials are more hazardous to bees in a moist climate, such as East Coast fruit-growing regions.

Time periods in brackets refer to the length of the residual toxic effect. Do not return bees to the field within that time period.

Additional label restrictions may apply; see pesticide label.

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 to adult bees:

• HT, highly toxic (acute LD50 < 2 μg/bee)
• MT, moderately toxic (acute LD50 2-10.99μg/bee)
• ST, slightly toxic (acute LD50 11-100μg/bee)
• NT, nontoxic (acute LD50 > 100μg/bee)

Source: Penn State Tree Fruit Production Guide