Herbicide Resistant

Updated: July 25, 2023

Managing Herbicide Resistant Common Ragweed (FS-474)

Common Ragweed (Ambrosia artemisiifolia) is a native summer annual weed of many cropping systems in the mid-Atlantic. It is often encountered as weed in agronomic crops as well as vegetable, orchards, roadsides, and abandoned fields. Common ragweed can thrive in lower fertility soils and is often more severe in reduced or no-tillage situations. In Maryland, populations of glyphosate resistant common ragweed were first confirmed in 2014. Resistance to ALS herbicides was also confirmed the same year. In most areas of Maryland, common ragweed has two-way resistance to both glyphosate and ALS chemistry. In 2017, pockets of three way resistant common ragweed plants were confirmed in parts of Delaware and the Eastern Shore of Maryland to PPO, ALS and glyphosate. Herbicide resistant common ragweed can be very difficult to control in agronomic crops, particularly soybeans. Authors: Benjamin Beale, and Matthew Morris; Title: Managing Herbicide Resistant Common Ragweed (FS-474)

Updated: April 8, 2022

Suggestions for Dealing With Herbicide Shortages for 2022

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

Updated: March 17, 2022

Understanding Glyphosate and Other Pesticides (FS-1193)

Recent concerns about the widespread use of glyphosate and its potential impacts have propelled this herbicide into the national spotlight. This article provides an overview of the regulatory processes glyphosate and other pesticides must undergo to ensure they do not pose unreasonable risks to human health or the environment. Author: Kurt Vollmer; Title: Understanding Glyphosate and Other Pesticides (FS-1193)

Updated: March 11, 2022

Control of Large Palmer Amaranth and Common Ragweed in Soybean or Corn (FS-1192)

Herbicide-resistant Palmer amaranth and common ragweed are two weed species that pose a major challenge to farmers. It is recommended that an effective postemergence herbicide be applied before these weeds are 3- to 4-inches tall. Palmer amaranth and common ragweed plants that exceed this height are challenging to control. This report summarizes research and discusses the challenges of managing large Palmer amaranth and common ragweed plants. Authors: Kurt Vollmer, Michael Flessner, Dwight Ligenfelter, Vijay Singh, Mark Vangessell, and John Wallace. Title: Control of Large Palmer Amaranth and Common Ragweed in Soybean or Corn (FS-1192)

Updated: November 16, 2021