Evergreens Help Block Spread Of Pesticide From Crop Fields

The finding comes at a time when regulatory agencies around the world are calling for farmers to utilize so-called “buffer zones” of unplanted ground or non-crop vegetation around crops to catch droplets of pesticide spray carried by the wind.

These rows of non-crop vegetation, or windbreaks, absorb pesticides that would otherwise contaminate adjacent plants, residential areas and water supplies, explained Franklin R. Hall, professor of entomology at Ohio State and lead author of the study. Urbanization has led to more houses being built close to farming operations, which makes the need for windbreaks even more important, he added.

At a recent meeting of the American Chemical Society in New Orleans, Hall and his colleagues reported their results. At windtunnel speeds ranging from 1.5 to 3.5 meters per second -- equivalent to a light breeze -- evergreen plants collected two to four times more spray droplets than broadleaf plants.

Hall said that as farmers spray pesticide onto crops, wind captures a portion of the mist, which contains a wide range of droplet sizes. “The smallest droplets can be carried off site by even a slight breeze,” he added. Trees, shrubs, and grasses planted at the edges of fields act like a strainer to filter the droplets from the air.

Hall and Tamer Ucar, a research associate at Ohio State, reviewed all previous windbreak research in scientific journals. They worked with Bruce Wight and Roel Vinning, both scientists with the United States Department of Agriculture’s Natural Resources Conservation Service (USDA-NRCS).

The researchers discovered that none of the dozens of articles compared the efficiency with which different windbreak plants capture sprays. To gather some comparative data, Ucar built a windtunnel at Ohio State’s Laboratory for Pest Control Application Technology in Wooster, Ohio, and hung branches from different plants inside.

He sprayed them with dye at windspeeds ranging from 1.5 to 3.5 meters per second, and measured the amount of dye captured. Evergreens -- plants such as pine trees which sprout cones and needles -- collected two to four times more dye than broadleaf plants, such as maple trees, which produce wide, flat leaves.

Hall said that evergreen needles offer a larger surface area for collecting sprays, as well as an aerodynamic shape. As air swirls around the needles, more droplets stick to these surfaces than if the air were gliding over the smooth surface of a flat leaf.

“The other good thing about evergreen trees is that they don’t lose their leaves,” said Hall. “So when farmers first apply pesticides in the early spring, evergreen foliage would already be there to help collect the spray and reduce off-site movement of pesticides.”

Next, Hall and his colleagues want to expand their studies of potentially useful windbreak species. They will also construct a longer windtunnel so they can gauge the performance of plant species and non-target organisms under an extended range of environmental conditions.

The researchers recommend that the government create a task force to review windbreaks as a viable pesticide drift mitigation strategy for the United States.

“Globally, there are only about five or six sites that have collected information on pesticides and windbreaks, and they’re not linked in any way,” said Hall. “So, our final conclusion was that we ought to bring various agencies together to discuss these research findings.”

“The opportunities to link the buffer zone and water quality initiatives -- as well as the stewardship programs in the EPA and USDA -- towards a common environmental goal seems enormous,” continued Hall. “But it is a multidisciplinary approach and will require some good task force planning to optimize our scarce resources.”

Hall and Wight are in the process of proposing such a task force to the EPA. They want to take advantage of United States satellite capability to study the effects of windbreaks around the United States and Canada.

Right now, only the Netherlands has mandated that its farmers use windbreaks. The English and Australian governments are starting to promote the idea.

In the United States, the NRCS runs a program that assists farmers in planting and maintaining windbreaks.

The Ohio NRCS office recommends plants like the eastern white pine, Norway spruce, or pin oak, among others. It also asks that farmers supplement windbreaks with flowering shrubs such as silky dogwood that provide habitat for wildlife.

For about 20 cents per foot, farmers in northwest Ohio can call on NRCS specialists to plant windbreak seedlings and maintain them for two years. At that cost, the typical 2000-foot stretch of windbreak runs about $400 -- which the agency says is comparable to what farmers would spend to do the job on their own.