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Ideas On Herbicide Resistance Shared Among Growers, Retailers, Consultants, And Industry At Regional Meeting

Posted: February 1, 2017

Participants to a listening session on herbicide resistance in Lancaster, PA inspired a productive and insightful discussion on the challenges, successes, and needs going forward for managing herbicide resistant weeds.

A listening session on Herbicide Resistance in the Northeast was held on January 18 in Lancaster, PA. The event assembled approximately 75 farmers, ag retailers, crop consultants, government employees and others from Pennsylvania, Delaware, New York, Maryland, New Jersey, and Ohio to discuss their experiences and ideas on managing the herbicide resistant weed problem. Most attendees were already dealing with resistant weeds, while others anticipate that weeds such as Palmer amaranth, waterhemp, and marestail will become a larger problem in their areas soon. This listening session was hosted jointly by Penn State, University of Delaware, and the Weed Science Society of America, with funding from the USDA, United Soybean Board and Syngenta.

Challenges Facing Resistance Management


Each participant was asked what they see as challenges to managing herbicide resistant weeds. Many felt one main challenge is that when individuals fail to identify, prevent, and control resistant weeds, it causes the weeds to increase and spread in the region. Some reasons for ineffective management were listed as: 1) growers not knowing when they have resistant weeds, 2) complacency towards the resistance issue because of the success of past herbicide technologies, or 3) not using appropriate prevention and management tactics to eradicate the problem early on before it becomes severe.

Several vegetable growers stated that limited herbicide options for resistant weeds in vegetable crops create an additional challenge. Some also felt that resistant weeds are spreading along roadsides and suggested that state DOTs could play an increased role in resistance management. While hand-pulling is often a necessary chore for aggressive weeds like Palmer and waterhemp, some growers are hesitant to hand-pull because of the time and labor involved. Others cited low commodity prices as an obstacle to investing the necessary inputs and energy to eradicate stubborn weeds.

Experiences In Managing Resistant Weeds

Preventing resistant weeds from entering new fields is key to managing the problem economically. One producer stating that “prevention will always be cheaper than eradication” when it comes to Palmer amaranth and waterhemp. Prevention strategies suggested at the meeting included:

  1. Scouting for problem weeds “early and often,”
  2. Avoiding the transport of potentially contaminated commodities, feed and supplies from areas where resistant weeds are prevalent (For example: Palmer amaranth is widespread in the Midwest, mid-south, and southeast), and
  3. Making sure that any harvest equipment that enters a field is not contaminated with pigweed seeds from other fields

In addition to prevention, participants described the practices that they’ve had success with once weeds do reach the field. Many said that Integrated Weed Management (IWM) tactics have been critical. The idea of IWM is to employ multiple crop management strategies that help optimize herbicide programs and increase the likelihood of success for specific weed species.

Some tactics mentioned include: scouting, choosing appropriate crop rotations that discourage weed growth, planting early to establish a competitive canopy, using multiple herbicide modes of action, considering mechanical control (i.e. cultivation, hand-pulling) and applying herbicides when the weeds are young. In vegetables, one experienced producer said that marestail control can be improved by extending the rotation and cultivating prior to planting – but some marestail still appears.

Several consultants stated that a healthy grower-advisor-salesperson relationship has been important for them in helping to ensure successful management. According to them, this collaboration fosters trust in recommendations by delivering a consistent message about what is needed for successful management.

What Else Can Be Done To Improve Resistant Weed Management?

Still, there is plenty more work to be done. There are specific things that agronomists, extension, industry, and state governments can do to help overcome the resistance challenge and make sure certain resistant weeds do not take hold in our state. Some suggested that state-supported programs could provide incentives or if necessary, regulations to encourage management of resistant weeds on individual farms. For example, several participants mentioned a desire to have Palmer amaranth added to the PA Noxious Weed List, as it is in other states including Delaware. They felt this might be necessary to motivate prevention and control before it spreads to neighboring farms or counties; through providing oversight to the movement of contaminated commodities, as well as state-funded eradication programs. Many also expressed a need for increased education about resistant weeds, especially to reach growers who may not have frequent interaction with state extension or crop consultants. Penn State Extension will continue to do our best to provide materials and recommendations regarding herbicide resistant weeds, and will strive to expand our reach to all stakeholders who can benefit from this information.

Below are several resources on managing herbicide resistant weeds:

Contact Information

Annie Klodd
  • Extension Associate
Phone: 814-863-7643
William S. Curran
  • Professor of Weed Science
Phone: 814-863-1014