Managing Pesticides to Protect Bees


Avoiding pesticide use is the best option for conserving pollinators. Most insecticides (and a handful of fungicides and herbicides) can kill bees directly or have sublethal effects that reduce the number of offspring a female bee can produce.

When pesticides must be used, actions that reduce their drift (off-target movement) and maintain buffer zones between sprayed areas and nearby natural habitat are critical. The resources on this page are intended to help reduce harm to pollinators wherever pesticides are being used.

Strategies for Reducing Harm to Pollinators From Pesticides

Careful timing of pesticide applications is the most basic consideration in reducing harm to bees. For example, wherever possible pesticides should not applied to blooming plants, or on plants where beneficial insects are active. Similarly, nighttime spraying, when bees are not foraging, is one way to reduce mortality. Low temperature periods also tend to be safer for spraying since most bees are not active. (However, keep in mind that the residual toxicity of many insecticides tends to last longer in cool temperatures. In addition, dewy nights may cause an insecticide to remain wet on the foliage and be more toxic to bees the following morning.)

Areas that must be sprayed with insecticides should also be kept free of flowering weeds prior to spraying because these weeds so that pollinators are not attracted into the area when spraying occurs. If possible, also avoid spraying recognizable bee nesting areas and butterfly host plants.

Finally, when applying insecticides, use the minimum recommended dose. Pesticides should never be applied at rates greater than those recommended by the manufacturer.

Managing Pesticide Drift

Pesticide drift (the off-target movement of chemicals into the environment) can continue to cause harm to bees and other wildlife more than a mile from where the original spraying occurs. Factors involved in pesticide drift include weather, application method, equipment settings, and spray formulation. Weather-related drift increases with temperature, wind velocity, convection air currents, and with temperature inversions. Low humidity and high temperatures promote drift through the evaporation of spray droplets and the reduction of particle size.

Even a light winds can contribute to pesticide drift. Wind-related drift can be minimized by spraying when wind speed is lowest (usually during early morning or evening hours). Pesticide labels will occasionally provide specific guidelines on acceptable wind velocities for applying a particular product.

Midday spraying tends to be less desirable because as the ground warms, rising air can lift the spray particles in vertical convection currents. These droplets may remain aloft for some time and may travel many miles.

Similarly, during temperature inversions spray droplets become trapped in a cool lower air mass and move laterally above the ground. Inversions often occur when cool night temperatures follow high day temperatures; they are often characterized by foggy conditions.

Optimal spray conditions for reducing drift occur when the air is slightly unstable with a very mild steady wind. Ideally, temperatures should be moderate and the air slightly humidity.

Spray application methods and equipment settings also strongly influence the potential for drift. Since small droplets are most likely to drift long distances, aerial applications and mist blowers should be avoided whenever possible. Standard boom sprayers should be operated at the lowest effective pressure and with the nozzles set as low as possible. Regardless of the chemical or type of application equipment used, sprayers should be properly calibrated to ensure that excess amounts of pesticide are not applied.

Organic Farming and Pesticides

It is important to note that even organic pesticides can harm pollinators. Pyrethrin, and spinosad, are both common pesticides in organic farming, and are broad-spectrum insect killers, destroying pest and beneficial species alike. Other organic-approved products are safer to use as long as they are not applied where pollinators are actively foraging or nesting. Less toxic pesticides include horticultural oils and insecticidal soaps.

Alternatives to Pesticides

Depending on the landscape, there are many things we can do to reduce or eliminate or limit pesticide use. A plant that is growing vigorously, with minimal stress, can avoid or outgrow many diseases and insect pests. Plant health starts with choosing species, and varieties appropriate to local conditions—and in the case of crop plants—with classical breeding for pest resistance.

It is also important to recognize and work with naturally occurring pest controls (beneficial insects that prey upon pests). A healthy and diverse landscape with sufficient natural habitat can support large numbers of native predators and/or parasites of insect pests. Pesticides may eliminate these beneficial insects where they are used, leading to chronic pest problems. Fortunately, many of the same strategies that protect pollinators will support these other native beneficial insects, further reducing the need for pest control.

For farms, maximizing crop diversity and practicing crop rotation to disrupt pest populations are some basic strategies to reduce pest problems. Planting resistant varieties is another option for some crops. More aggressive practices include the use of sticky traps, pheromone traps, and mating disruption pheromones for certain insects.


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How to Reduce Bee Poisoning from Pesticides

Deciding which pesticide product to use can be a complex process. This detailed guide, produced jointly by the extension services of Oregon State University, Washington State University, and the University of Idaho, offers detailed guidance on how to select and apply insecticides. Extensive tables list the toxicity to bees of dozens of chemicals and how long after application they remain hazardous to bees in the field. To view PDF, click here.


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long horned bee (Melissodes sp.) on sunflower by Mace Vaughan