While weed shifts are certainly more prevalent than with other forms of tillage, following some common-sense strategies should help you successfully navigate through a changing weed spectrum.
The problem is your no-till weed control program dictates a shift to surviving weeds and not to those you effectively controlled.
“All weed control programs select or separate out weeds that are able to survive,” says Bob Hartzler, an Iowa State University weed scientist. “Weeds that survive a control tactic, such as a particular herbicide chemistry, produce seed and therefore increase populations. Weeds that are killed fail to produce seed, reducing their populations. So your weed spectrum shifts to the surviving weeds.”
When dealing with weed escapes, Dirk Drost, a technical brand lead for Zeneca Ag Products, suggests rotating herbicide chemistry and using tankmixes to keep weed gaps under control.
One of the worst weed shifts Midwestern no-tillers witnessed in the ‘90s dealt with waterhemp. This obscure relative of pigweed quickly became a major weed problem.
When ALS-inhibitor herbicides came on the market in the late ‘80s, a number were very effective against waterhemp. But widespread use of ALS inhibitors caused a weed shift within a few years. Mike Owen, another Iowa State University weed scientist, says infestations of common waterhemp soon became a major weed problem throughout the Midwest.
While he says reduced tillage systems contributed somewhat to the weed shift, Owen believes selection pressure from the ALS inhibitors was the major factor. These herbicides demonstrated excellent activity on a…