After last year's wildfires, expect more weeds on rangelands. Here are some strategies to cope.

Last year's wildfires in the West could fuel a healthy crop of weeds on those rangelands this growing season, says Steve Dewey, a Utah State University Extension weed specialist.

“Noxious weeds often invade and spread rapidly in response to the natural disturbance of fire,” Dewey says. In a recent study in central Utah, the amount of squarrose knapweed on rangeland nearly doubled within one year following a wildfire, Dewey reports.

Weeds to watch for after a fire include: yellow starthistle, knapweeds, medusahead, dyer's woad, toadflax, thistles, hoary cress, leafy spurge and many others.

On the bright side, fire can actually help control of some weeds, Dewey says.

His research indicates treating squarrose knapweed with herbicides soon after a wildfire resulted in excellent weed control. More importantly, the level of control was much higher than with herbicides alone.

“In other words, the combination of fire followed by a herbicide application resulted in much better squarrose knapweed control than if we sprayed and had no fire,” Dewey says.

In another study, knapweed control two to three seasons after a single herbicide application (Tordon + 2,4-D) averaged only 20% on non-burned land, compared to 86% on land where the application was preceded by burning, he adds.

In that same study, forage grass yields were five times greater on plots that were both burned and sprayed (2,307 lbs./acre) compared to 456 lbs./acre on plots that were just sprayed.

“Whether a wildfire will result in the improvement or worsening of your weed problem depends on what you do in the first few months,” Dewey says.

Dewey recommends land managers inspect burned areas for weeds soon after any fire. If a weed problem is noted, map where the infestations are and start control efforts promptly.

He says fall or spring applications of herbicides work well to control weeds. But, he adds, “For best results follow label instructions for the proper application timing on each weed species.”

“If nothing is done following a fire, the weed situation is almost certain to worsen. If fire is combined with timely weed control efforts, the results can be impressive,” Dewey says.