Herbicide Resistant

The shortage of glyphosate (Roundup, Gly Star, etc.) and glufosinate (Liberty, Interline, etc.) herbicides are forcing farmers to seek other options for burndown and postemergence spray. No one anticipated this shortage and very little research has been done to address this issue. Many of us had to dust off our notes from the early 1990’s, the time before cheap glyphosate was available. One thing is certain, alternative weed control options will require more targeted management. The key is to plan ahead, select herbicides based on the weeds in the field, and make timely applications. Your mindset needs to be that you are not substituting a herbicide for glyphosate, rather you are using a different herbicide that has its own set of recommendations and limitations. Author: Kurt Vollmer, Univeristy of Maryland Extension Weed Management Specialist, and Mark Van Gessel, University of Delaware Weed Management Specialist; Title: Suggestions for Dealing With Herbicide Shortages for 2022

Herbicide resistant common ragweed (Ambrosia artemisiifolia L.) is prevalent on the Lower Eastern Shore of Maryland and other areas in the region. In 2019, common ragweed populations on the Eastern Shore of Maryland and Delaware were found to have two or three-way mode-of-action resistance to herbicides. They were resistant to glyphosate (group 9), cloransulam (Firstrate; group 2 “ALS inhibitors”), and/or fomesafen (Reflex; group 14 “PPO Inhibitors”). Early-season management of common ragweed is strongly dependent upon reducing seed emergence and controlling ragweed populations prior to soybean planting. However, due to the limited herbicides with efficacy against common ragweed, it is even more critical to utilize alternative and multiple means of control.

In Maryland, populations of common ragweed have developed resistance to three herbicide groups, Group 9 (glyphosate), Group 2 (FirstRate, Synchrony), and Group 14 (Flexstar, Valor). These herbicide-resistant populations limit options for effective postemergence control. Even though alternative herbicides are available, control can be inconsistent when applied to common ragweed plants exceeding 4” tall (Figure 1). 

Greenhouse Herbicides for Vegetables

Important Herbicide Groups for Commercial Vegetables

Herbicide Effectiveness on Common Weeds in Vegetables