Pollination for crops and pesticide use

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Pollination is the crucial first step toward obtaining good yields. Most fruits grown in Michigan, including peaches, pears, apples, cherries, blueberries and cranberries, all require insect pollination to ensure good fruit set. California almond growers paid as high as $160 per colony of honey bees spring of 2006, and although we won’t be that high in Michigan, our prices for pollination will also be affected this year due to overwintering mortality. Last year (winter of 2004) the national average was 50% mortality.

To find a beekeeper nearest to you, please check the web site http://beebase.cyberbee.net where you can search beekeepers that provide pollination in Michigan. You can also register your needs for pollination so that beekeepers can find you. A website with information on bee biology, research and beekeeping is also available at MSU (http://cyberbee.msu.edu). To learn whether your fruit crop would benefit from bee pollination, please check the online pollination book at http://gears.tucson.ars.ag.gov/book/index.html.

Growers want to maximize crop production and beekeepers want to maintain their colonies healthy and productive. Sometimes there can be a conflict between the two when bees are placed in fields for pollination and spraying is needed for disease or pest control. Because bees are insects, most insecticides will have some toxicity to bees, so close cooperation among growers, pesticide applicators, and beekeepers is needed to protect bees against poisoning.

Bee poisoning can be subtle

Some pesticides cause direct kill of foragers. This happens when bees are on flowers when the pesticide application is conducted, or when the pesticide used is highly toxic to bees. The highly toxic pesticides actually leave no evidence because nearly all bees die in the field, before bees make their way home. Other types of pesticides allow bees to return home, and then die inside the hive. This type of poisoning is the easiest to diagnose, with a large pile of dead bees in front of a bee hive, usually with their tongues sticking out. Some chemicals do not directly harm adult bees, so they are brought back to the colony and cause damage to young, immature stages of bees (brood). Captan is of this type and does not kill adult bees but larvae exposed to it die or develop into malformed adults. The French beekeepers have experienced the “mad bee disease” recently, in which millions of bees simply become disoriented and not finding their way home. A suspected culprit was thought to be the chemical Gaucho (imidacloprid) applied to sunflowers to protect against parasites, but there is still much discussion about this issue. The French government in 2001 ordered a two-year extension of a ban on spraying this chemical on sunflowers, to allow more study of its impact on the nervous systems of bees. The take-home message is that diagnosis of bee poisoning can be difficult, and growers should take care with any use of pesticides during bloom, and follow the directions for bee safety.

Formulations and time of application

As a rule of thumb, if you have the same pesticide in both dust and liquid form, use the liquid form. Because hairy bee bodies maximize pollen collection, pesticides applied as dusts are more hazardous than sprays to honey bees. Micro-encapsulated pesticides are worse because bees sometimes mistake these granules as pollen and bring them home, causing long-term, chronic damage to the entire colony. ULV formulations can be more toxic to bees because of its higher concentrations, and daytime aerial application of pesticides can be bad news for bees, because many bees in flight will be hit.

Time of application can be important because many foragers will die when sprayed pesticides land on bees directly or is mixed with nectar and bees are foraging on it. Consider working with beekeepers on the spray schedule. Give him or her some options considering the chemical sprayed and the schedules of both the grower and beekeeper. For example, tell the beekeeper a spray is really necessary but you are concerned about his bees. “Should I spray tonight 7:00 to 9:00 PM, when bee activity is minimal; or do you think it is better to close the colonies tonight and I spray tomorrow morning 7:00 to 9:00 AM, and then release the bees around noon?” This type of discussion will often lead to satisfactory comprise for both sides. It does not cause any harm to bees for the colonies to be closed for a few hours. During a very hot day, overheating can be an issue, but can be worked out also, if water is provided abundantly (use soaked burlap at the hive entrance and apply water every 2 hours in July-September).

Use a less toxic chemical for bees

Use a specific pesticide targeting the pest you want to control is often better for you (less harm to other beneficial insects), and for the beekeeper. Most pesticides are labeled as not toxic, moderately toxic, or highly toxic to honey bees. Remember that some fungicides, as well as herbicides, can be toxic to bees.

A list of pesticides of low, moderate and high toxicity, as well as considerations for both growers and beekeepers, can be found online at http://ohioline.osu.edu/hyg-fact/2000/2161.html

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