Minimizing Pesticide Risk to Bees in Fruit Crops
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Extension Bulletin E3245 • New • May 2015 Minimizing Pesticide Risk to Bees in Fruit Crops Photos by Zachary Huang (first two, left) and Jason Gibbs (second two, right), MSU Entomology Emily May, Julianna Wilson and Rufus Isaacs. Department of Entomology, Michigan State University. INTRODUCTION SUMMARY Pollinating insects, of which bees are the most important, 1. Bees are essential for pollination of many fruit crops. contribute significantly to the yield and quality of fruit crops in the United States. Pollination services provided by bees 2. Bees and other pollinators can be harmed by some are worth billions of dollars annually to fruit crop industries pesticides used to manage insects, mites and diseases across the nation. Fruit crops vary in their need for bees to in fruit crops. deliver pollen for pollination, but most — including apples, 3. Growers can reduce pesticide risk to bees through blueberries, cherries, strawberries and raspberries — will these approaches: produce larger and more even fruit if their flowers are well - Develop and implement a pollination contract with visited by bees. For all these crops, having healthy bees your beekeeper. to provide pollination is essential for their production, so - Use integrated pest management (IPM) to reduce protecting bees from pesticide risk is an important part of the need for sprays. growing fruit crops. - Avoid pesticide sprays during crop bloom. This document provides information to help growers - Apply pesticides after sunset or before sunrise, or make informed decisions about how to minimize the risk when air temperature is below 50°F. of pesticides to bees. A list of insecticides and fungicides - Select the least toxic pesticides and formulations that are registered for use in the north central region of the when possible. United States is provided in the back of the document. - Reduce drift onto areas outside crop fields. Types of bees that provide pollination - Remove flowering weeds from crops. Fruit plantings are typically pollinated by a combination of - Provide bee-friendly habitat away from crops. wild and managed bees (Figure 1). More than 500 species of bees are present in the Midwest, and about 30 to 50 species are important contributors to the pollination of fruit crops. 2 Minimizing Pesticide Risk to Bees in Fruit Crops Figure 1. Overlap of the activity periods of various wild and managed bee species with spring crop bloom, and their potential activity periods through the rest of the season. Photos by Jason Gibbs Most fruit plantings are visited by a community of wild parasitic mites. Now fruit growers typically rent honey bee bees that live in and around the farms and gardens where hives from beekeepers for pollination and arrange to have fruit crops are grown. The main bee species managed for hives delivered when crop plants are at early bloom and pollination is the European honey bee (Apis mellifera). Some removed at petal fall. growers may also keep managed populations of solitary In addition to managed honey bees, some growers manage mason bees (Osmia species) or purchase commercially solitary mason bees (Osmia species) for pollination of available bumble bee colonies (Bombus impatiens). tree fruit. Mason bees can be induced to nest in paper or Many types of bees contribute to the pollination of fruit cardboard tubes or in holes drilled in wood, where they crops. Some of these are wild and unmanaged, providing overwinter and emerge the following spring or summer. This a natural source of pollination. Others can be managed emergence can be timed to coincide with flowering of the using nesting structures that enable growers to have a high crop, and the bees then remain active for up to 4 weeks. abundance of bees in the local area (Figure 2). Some growers purchase colonies of bumble bees from The honey bee is by far the most important species for commercial suppliers that continuously rear these bees. fruit crop pollination because hives are portable and can be Colonies are purchased in time for the pollination needs of transported into and out of fruit plantings. In the past, feral the target crop, providing an active workforce in the field or unmanaged colonies of honey bees played a major role during bloom. These colonies generally remain active for in pollination, but populations have declined because of about 6 to 8 weeks. Michigan State University Extension 3 Figure 2. Three types of managed bees that can be used to pollinate fruit crops. L-R: honey bee hives, bumble bee colonies, and mason bees. Photos by Rufus Isaacs, MSU Entomology A variety of wild bee species are active throughout the Social bees have the advantage of having many foraging growing season, and some of them are well-suited to bees across the landscape; if some bees die while foraging, provide pollination of crop flowers. Most of these species the colony is likely to have other bees available to take their cannot be commercially managed because they nest in the place. If a solitary bee is killed while foraging, there are no ground. Some have been found nesting in the grass-free other adult females that can take her place. strips under the fruit crop or in adjacent habitat. These bees can fly to blooming crop plants within their flight range. PESTICIDE EFFECTS ON BEES Pesticide application is an important consideration for both Bee biology and behavior may affect responses beekeepers and fruit growers because both have a stake to pesticides in maintaining healthy bee populations. This requires an Bee body size, nest location (above or below ground), flight integrated approach to pest management by growers, who season (what time of year the bee is active) and sociality need to control target insects while doing the least harm to (whether a bee is solitary or social) can all affect how bees the pollinators. Bees are sensitive to many of the chemicals are exposed to and affected by pesticides. used to control pests, whether on the plants that they visit Large-bodied bees, such as honey bees and bumble bees, to collect nectar and pollen or in the areas where they are can generally fly greater distances than smaller bees in nesting. search of pollen and nectar resources. Honey bees have Pollinator stewardship, as part of an overall IPM strategy, can been found to fly more than a mile in search of rewarding allow growers to manage diseases and insect pests in their flower patches, but many smaller wild bees fly no farther crop while also minimizing risk to pollinators. than the length of a football field in search of food. Larger bees may also be able to tolerate higher levels of certain Which pesticides affect bees? pesticides than smaller bees, but their broader flight range Growers use many groups of pesticides to protect their means that they cover more ground and have the potential crops, including insecticides for controlling pest insects, to be exposed to a wider variety of pesticides. miticides for pest mites, fungicides for fungal diseases and The social structure of bees is another important aspect that herbicides for weeds. These pesticides are important tools determines how they respond to pesticides. Honey bees are for managing crop pests in fruit plantings, but they may also the classic example of social bees that have a single queen pose a risk to bees. laying eggs for the colony and many adult female offspring Insecticides are the pesticides most likely to be toxic to (workers) taking care of other tasks such as caring for brood bees. Bees can be exposed to insecticides when materials and foraging for nectar and pollen. In contrast, many wild are sprayed directly onto them or drift onto or near hives, bee species are solitary, meaning that a single adult female when bees come into contact with residues on plant lays eggs, cares for offspring and makes foraging trips. surfaces, or when bees collect chemicals while foraging for 4 Minimizing Pesticide Risk to Bees in Fruit Crops food or water. By law, and as described in the restrictions Tank mixes of pesticides may cause increased risk to bees on labels, the use of insecticides toxic to bees is restricted through synergistic effects, which make the toxicity of the during crop bloom when bees are actively foraging. Each mixture greater than that of the individual components. label will provide specific guidance on the restrictions, There is evidence that fungicides in the Fungicide Resistance which are based on the insecticide’s toxicity to bees. Table 1 Action Committee (FRAC) Group 3 can make insecticides provides information on the toxicity of various insecticides more toxic to bees. More recently, laboratory studies with used in fruit crops, ranked from very low risk to high risk to newer products have demonstrated this synergism for bees. additional combinations of pesticides. Research on the Fungicides are generally considered of limited risk to impacts of tank mixes on bees and their colonies under field bees, and thus their use during bloom has been assumed conditions is still ongoing. to be relatively safe to pollinators. Recent research For all pesticide applications, be sure to follow the label suggests, however, that certain fungicides, used alone or instructions on safety to bees and other pollinators. in combination with other pesticides, can have direct or Labels can be found at www.cdms.net/. See below for indirect harmful effects on bees. They may disrupt adult bee more details. foraging behavior or, when residues are brought back to hives and fed to larvae, they can affect bee development. What is the risk? To minimize the exposure of adult and immature bees The risk of toxic effects from pesticides is a combination of to fungicides, growers should follow integrated disease the toxicity of the pesticide — its inherent ability to harm management practices including the use of risk models to a bee — and the amount of exposure that a bee receives.