Golf course weeds are developing resistance to the herbicide glyphosate

A report in the current issue of the journal Weed Science focuses on a biotype of bluegrass found at the Humboldt Country Club in Humboldt, Tennessee. This course had been treated with glyphosate once each winter for nearly 20 years to kill bluegrass weeds while the course's bermudagrass turf was dormant.

Turfgrass managers have selected glyphosate as an economic and effective choice for weed management. Other herbicides have not been used as often for weed control, and so many grasses are repeatedly treated with glyphosate. As a result, these weeds have become resistant to this herbicide.

Researchers collected samples of glyphosate-resistant bluegrass from the Tennessee golf course. They then tested this grass and samples known to still be susceptible to the herbicide. In laboratory experiments, the susceptible samples showed a higher chemical concentration than did the resistant species.

In the greenhouse, the samples were treated with six different concentrations of glyphosate. While the susceptible sample was 95 percent controlled at half the concentration that had been used on the golf course, the resistant sample was only 76 percent controlled at the highest concentration tested -- eight times more than that used on the golf course.

Bluegrass is a self-pollinating species. Therefore, pollen dispersal or seed movement that would spread the resistant traits developed in this biotype is unlikely. But strategies for alternative weed control are needed to prevent new resistant biotypes from developing.