Using growth-regulator herbicides to sterilize grassy weeds instead of kill them may be an economical and environmentally sound weed control strategy, says a scientist at the USDA-ARS Fort Keogh Livestock and Range Research Laboratory in Miles City, MT.

Rangeland ecologist Matt Rinella points out that annual grasses such as Japanese brome, cheatgrass and medusahead are harming millions of acres of grassland in the western U.S. The herbicides currently used to control them also sometimes damage desirable perennial grasses, he adds.

But growth regulators, often used to control broadleaf weeds in wheat and other grass crops, don’t greatly harm desirable perennials, says Rinella. He and his colleagues knew that, when those herbicides were applied to cereal crops just before seed formation, the plants produced far fewer seeds. So, along with Robert Masters of Dow AgroSciences, they conducted a study on late-season applications to Japanese brome.

In greenhouse experiments, they tested dicamba (Banvel/Clarity), 2,4-D and picloram (Tordon) at typically used rates. They found that picloram reduced seed production nearly 100%. Dicamba was slightly less effective, but still nearly eliminated all seed production, while 2,4-D was much less effective.

Since annual grass seeds only survive in soil a year or two, it should only take one to three years of herbicide treatment to greatly reduce the soil seed bank, says Rinella.

He recently finished field tests that support the greenhouse results, and also tested aminopyralid (Milestone), finding it as effective as picloram. Next he’ll test lower doses of the herbicides in an attempt to cut costs and reduce damage to broadleaf plants.