Producing crops to meet consumer quality demands means that growers may use chemicals to control pests and diseases. Some of these products may be harmful to bees if used incorrectly. To demonstrate good environmental stewardship, growers need an understanding of the issues presenting risks to bees and of strategies to minimize the risks. Knowing where to find key product information and how to interpret it can help growers make sound choices regarding the application of effective products.
The Importance Of Pollinators To Our Food Supply
Insect pollinators, including bees, are important to our food supply system, both in terms of economics and of production. Pollination by bees alone contributes to more than $15 billion in crop value annually . Many crops require biological pollination, including fruit, nut and vegetable crops. Undoubtedly, our grocery store shelves would look quite different without bees pollinating our crops.
Understanding Colony Collapse Disorder
Concern about bee health is widely publicized, due in large part to our dependence on bee pollination for food production. Currently, much research and attention is focused on Colony Collapse Disorder (CCD). CCD describes a syndrome in which an unexpected, sudden loss of overwintering adult bees occurs in a mature colony, though the queen and brood generally survive . These colonies are drastically weakened by the loss of the adults. Not all colony losses are attributed to CCD. CCD is diagnosed when colony loss is noted in the absence of dead bees, implying that the bees did not return to the hive .
Multiple factors contribute to CCD, though the exact mechanism is not well understood. Among the factors believed to play a role are:
- Parasites: The Varroa destructor mite is found in association with CCD hives and is considered to be a serious threat to honeybee health.
- Pathogens: CCD hives have greater numbers of pathogens present , including Nosema fungal infections. Viral infections are also correlated with CCD, including systemic Tomato Ring Spot Virus .
- Varroa/Nosema disease complex: Interactions between parasite and pathogen are suspected .
- Hive management: Concerns range from strong reductions in genetic diversity to the impact of long-distance transport of hives for pollination services.
- Pesticide toxicity: In previous decades, concern focused on risks from the use of organophosphates and other classes of pesticides. Recent concern has focused on the neonicotinoid class of chemicals.
- Habitat loss: Expansion of agriculture, changing agricultural practices (elimination of wind rows and buffer strips) and housing has led to a reduction in native and wild areas, which serve as rich sources of food for foraging bees.
- Hive nutrition: Nutrition is often provided in the form of commercial foods.
Understanding Pesticide Toxicity
Some pesticides are known to be harmful to bees and should be used in a way that minimizes exposure. Labels for these products include bee hazard statements. Current EPA labeling describes bee toxicity by degree, using the following terms: low toxicity, toxic, highly toxic and very highly toxic.
Harmful exposure occurs in several ways. Some products are harmful upon direct exposure; the exposure risk occurs at the time of application. Other products are harmful through residual exposure; the exposure risk occurs for some time after application. Some products present both direct and residual risks. Remember that bees are often attracted to weeds blooming in the vicinity of the treated crops; product applied to weeds may also present an exposure risk to bees.
Current EPA labeling addresses exposure routes by describing when to avoid application. For products with direct exposure risk, bee hazard statements indicate that the product should not be applied when bees are actively visiting or actively foraging in the treatment area. For products with residual exposure risk, the label will indicated that the product should not be applied when bees are visiting or foraging in the treatment area. Note that the use of the term “actively” is the key word that indicates a direct exposure risk. Growers are strongly encouraged to thoroughly read and follow all product label instructions.
It’s worth noting that some application methods (e.g., granular) and some product classes (e.g., fungicides and surfactants) are not currently subject to bee hazard evaluation by the EPA. Therefore, the absence of bee toxicity or hazard language on a product label should not be interpreted as a lack of risk. Consult your supplier to address specific concerns.
Understanding Pollinator Foraging Behavior
For most bees, including commercial honeybees, foraging behavior follows a predictable, daily pattern . Feeding starts just before or very close to sunrise, peaking in late morning. A second activity peak may occur in the early afternoon. Foraging is greatly diminished by early evening and essentially non-existent at night . Bees tend to collect pollen in the morning and nectar throughout the day. Bumble bees are active later into the afternoon than honeybees.
Foraging behavior of bees is strongly tied to temperature and weather. Beekeepers view 55˚F as the minimum temperature at which foraging will occur . Bumble bees have a wider temperature range, with potential for foraging as low as 47˚F to 50˚F. Bees will continue to forage under light rain and drizzle, though winds of 10 to 15 mph will slow activity.
Putting The Information To Work
Not all pesticides present a risk to bees and other pollinators. When the product of choice does present a risk, steps should be taken to minimize that exposure risk.
Responsible application can be achieved by considering the following points:
- Review product labels for a full understanding of the direct and residual toxicity of selected pesticides to pollinators.
- Plan applications to minimize residual exposure.
o Select products with lower toxicity and residual exposure risk for outdoor applications.
o Avoid outdoor application of toxic, highly toxic and very highly toxic products with residual risk exceeding 12 hours to crops when flowers are open and bees may visit the area.
o Avoid application of toxic, highly toxic and very highly toxic products with residual risk if the crop will come into bloom outdoors within the residual risk period.
- Plan applications to minimize direct exposure.
o Conduct outdoor pesticide application as late in the day as possible, preferably in the early evening.
o Alternatively, outdoor applications could be made when temperatures are expected to remain below 50˚F for the entire application period.
- In all cases of outdoor application, a visual check for pollinator presence should be performed.
- Avoid application to nearby, flowering, non-crop plants (including weeds).
- Provide a 48-hour courtesy notification to area beekeepers regarding your application plans and measures taken to avoid toxic exposures (direct and residual).
This information was first published as a GGSPro technical bulletin on February 11, 2014.
- Honey Bees and Colony Collapse Disorder. USDA, ARS. Web. 30 January 2014.
- Protecting Pollinators: Why and How Pesticide Applicators Can Help Them. North American Pollinator Protection Campaign. 2010.
- USDA. 2012. Colony Collapse Disorder Progress Report.
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