Evergreens touted as a pesticide buffer

Trees, shrubs and grasses planted at the edges of a field act like a strainer to filter droplets from the air.

November 19, 1999
Web posted at: 1:53 p.m. EST (1853 GMT)

Farmers should plant evergreen trees, such as pines and cedars, around their crops in order to reduce the spread of pesticide sprays beyond their fields, according to an Ohio State University study.

This is the first such study that compares the efficiency with which different windbreak plants capture pesticide sprays. Evergreen trees catch two to four times more pesticides than broadleaf plants such as maple trees, which produce wide, flat leaves, according to the study.

As farmers spray pesticide onto crops, wind captures a portion of the mist, which contains a wide range of droplet sizes. "The smallest sizes can be carried off site by even a slight breeze," said Franklin Hall, a professor of entomology at Ohio State and lead author of the study, in a statement.

Trees, shrubs and grasses planted at the edges of a field act like a strainer to filter the droplets from the air. To determine which type of plants capture the most pesticides, Hall and his colleagues built a wind tunnel at a university research lab.

As the air swirls around the needles, droplets stick to them, as in this picture of ice droplets on pine needles.

The researchers hung branches of various plants inside the wind tunnel and then sprayed dyed pesticides into the tunnel at speeds ranging from 5 to 12 feet per second (equivalent to a light breeze) and measured the amount of dye captured.

The researchers determined that the evergreens captured two to four times more dye than the broadleaf plants because evergreen needles offer a larger surface area for collecting sprays, as well as aerodynamic shape.

As the air swirls around the needles, more droplets stick to these surfaces than if the air were gliding over the smooth surface of a leaf, the researchers report.

"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."

Only the Netherlands requires its farmers to use windbreaks. The English and Australian governments are starting to promote the idea. In the United States, the U.S. Department of Agriculture Natural Resources Conservation Service runs a program that assists farmers in planting and maintaining windbreaks.

Copyright 1999, Environmental News Network, All Rights Reserved

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