On Target

A State University of New York College of Environmental Science (SUNY-ESF) study has compared the herbicide deposition of four conventional vegetation management techniques (cut-stump, basal, high-volume foliar and low-volume foliar) on New York rights of way (ROWs). Trees were treated with herbicide mixes containing a fluorescent dye to track and measure how much chemical landed off-target with each application technique.

The research results were surprising. On a per-tree basis, basal and cut-stump treatments produced off-target deposition of nearly six times more herbicide than high-volume foliar treatments, and almost 70 times more herbicide than low-volume foliar treatments.

“Foliar treatments can give the wrong impression,” says Ben Ballard, research scientist with SUNY-ESF, “because although you're putting a tenth of the active ingredient down compared to a cut-stump or basal treatment, the area affected — at least in the short term — looks like a lot more.” Ballard explains that what's really happening is vegetation cover catches some of the chemical. This can be seen as brown on the landscape, but most of the area is only temporarily affected and vegetation comes back.

“What's important to note is that the research shows that because they use different application methods and levels of chemical concentration, foliar treatments inherently deposit less herbicide off-target than cutstump and basal treatments,” Ballard concludes.

While foliar techniques deposited significantly less herbicide off-target than the basal and cut-stump applications, the research also showed a notable difference in herbicide deposition between the high- and low-volume foliar techniques. The high-volume foliar application of Tordon K (.06 percent picloram active ingredient by volume) and Garlon 4 (.23 percent triclopyr active ingredient by volume) deposited 11 percent of herbicide off-target, while the Arsenal (.14 percent imazapyr active ingredient by volume) and Accord (2 percent glyphosate active ingredient by volume) low-volume foliar techniques deposited only 4 percent of herbicide off-target.

Researchers found that the deposition difference between high- and low-volume foliar techniques can be minimized by making minor adjustments in application technique. For example, some areas in New York use a technique called a low-volume hydraulic application. With this technique, applicators use the same high-volume equipment but make the application at a lower pressure and with a chemical mix that's closer to the mix of a traditional backpack treatment.

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