The Beekeeper’s Companion Since 1861
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Beekeeping Topics

Pesticide Spraying

- March 1, 2015 - Ray Nabors - (excerpt)

I was asked by my friends at the local beekeeping club and some of our master garden students to address the issue of pesticide exposure avoidance for honey bees. The reason this article is appropriate now is that planning ahead is essential to avoiding pesticide kills of honey bees.

I reside in an area where agricultural pesticide use would be considered intense. Surrounded by 2.5 million acres of crop land where almost every acre is sprayed with at least one insecticide every season. Many acres have an application of fungicide and every acre receives multiple herbicide applications. You might assume that bees could not be kept here. That is not the case. Bees thrive here and produce a rich harvest of cotton and soybean nectar and pollen.

What is the secret? Communication plays a major role in avoiding pesticide kills. Hobby beekeepers are usually located on the outskirts of a town, village or city. These locations may have truck crops, orchards or farms in the vicinity. Many of the bee kills I have seen were the result of a neighbor or the beekeeper spraying their own garden at the wrong time or in the wrong manner. There are ways to avoid a catastrophe.

First, let everyone in your vicinity know that you have an apiary. Many cities have abandoned ordinances prohibiting honey bees. Beekeepers are becoming more common in urban areas. Pesticides are used more on golf courses than any farm. Pesticides are also used on lawns, trees and shrubs more often than on farms. Urban and suburban locations are dangerous for honey bees. These are also the most likely locations for hobby beekeepers.  Enlist your neighbors help in keeping your bees healthy by reducing chemical exposure.

Most modern pesticides available over the counter are low toxicity chemistry for people. Many of these that are not insecticides are low toxicity to bees. Any herbicide available for general use and for sale at the garden center is not toxic to honey bees. The herbicide Roundup® is an example of modern chemistry; it is extremely low toxicity to any living thing but plants. Chemical toxicity is measured in LD 50. That is Lethal Dose to 50 % of the organisms tested. Roundup has an LD 50 of 10,000. That means it takes 10,000 milligrams per kilogram of body weight to cause a lethal effect. By comparison, table salt has an LD 50 of 3,000 and a bar of bath soap has an LD 50 of 2,000 (5 times more toxic than Roundup). None of these chemicals are dangerous to people. Only the soap is dangerous to bees.

Most fungicides are not toxic to bees. However, a few commercial fungicides have been found to hurt bees when directly sprayed upon them, especially when growers add pesticides to a “tank mix” that was supposed to only contain the fungicide. Modern pesticides often include an adjuvant. These additives help spread out water and dissolved chemicals over the top of a waxy leaf surface. They also increase pesticide absorption or glue the chemical component to the leaf. These plant medicines often require a lower pH to work well. An adjuvant can be made of detergent, vegetable oil, liquid fertilizer or an acid.  If you have a garden and want to apply an insecticide, fungicide, or herbicide, use an adjuvant and apply at dusk to avoid bee exposure.

This is a recipe for a homemade adjuvant that will make any plant protection product work better, absorb faster and not hurt the bees or plants unless you use too much. To each gallon of water for any spray solution use 1 teaspoon each of vinegar, dish detergent and salad oil. Any more than 1 teaspoon can harm your plants or your bees. If you want to make an organic insecticide, use a 5% solution in water of salad oil with a teaspoon each of detergent and vinegar. This solution is harmful if sprayed on bees. The “spray at dusk” rule is absolute on our little farm.

Commercial farming can be organic, but that is a niche market. Most modern farms use chemistry. Herbicides are most common and least harmful to bees. However, all insects, including bees, have a waxy cuticle to keep their moisture inside. It is a lot like skin without which vertebrates would dry out and die. Detergent will soften and dissolve wax just like it dissolves grease from dishes and dirt from clothes. This allows the chemical treatment to penetrate a leaf or insect. Oil mixes with the wax cuticle of plants and insects facilitating the penetration of said cuticle. Together detergent and vegetable oil spread out the spray droplet and penetrate the plant or insect helping the product work much more efficiently. Most chemical reactions will work better at a lower pH so the vinegar will speed up the reaction.

The most common insecticides available at the garden center are …