Do herbicide resistant GMOs lead to higher herbicide usage?

Expert response from Shawn Askew

Extension Specialist and Associate Professor, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University

Wednesday, 24/09/2014 00:00

Generally speaking, probably not. Glyphosate, the active ingredient in most herbicides used on GM crops, is used at a rate of 0.9 to 1.9 pounds per acre. By comparison, standard preemergence herbicide mixtures are typically used at two to more than three pounds active ingredient per acre. Comparisons, however, can also be made to the contrary. If you were using glyphosate for Johnsongrass control, for example, and compared that with nicosulfuron, the glyphosate would equate to 40 times more active-ingredient weight than the nicosulfuron. The relationship of herbicide usage all depends on the herbicides being compared.

The problem is that low-use-rate herbicides like nicosulfuron, like all herbicides, control only a specific set of weeds. To produce a harvestable corn crop, farmers must use an assortment of conventional herbicides and nonchemical methods to control the weed population at a given site. Glyphosate can replace most of the conventional herbicides that were once used. Since some of those herbicides were used at rates higher than those of glyphosate, and others were used at rates lower than those of glyphosate, the net result of GM crop introduction would be a small change in the amount of herbicide used.

Another missing component in most discussions related to herbicide "amount" is the relative biological activity of one herbicide compared with another. Some herbicides are applied at very low rates but have extremely high biological activity. There is currently no way to quantify biological activity in terms that would be meaningful for this discussion, but suffice it to say that simply knowing the total active-ingredient load per acre is not necessarily a meaningful assessment of an herbicide’s impact on the environment.