Agriculture and Natural Resources-Weed Science

Issue:  The U.S. Environmental Protection Agency (EPA) and Weed Science Society of America (WSSA) have worked together in recent years on a number of weed management issues facing farmers, natural resource managers, and weed scientists.  The Mid-Atlantic Region of the United States has been dealing with herbicide resistant weeds since 1972 when triazine resistance was identified in Maryland. Glyphosate- resistant horseweed was identified in 2000 in Delaware and, more recently, acetolactate synthase (ALS) -resistant smooth pigweed, ALS-resistant common chickweed , and glyphosate-resistant Palmer amaranth  have been confirmed in the region. While, glyphosate-resistant weed species in grain crops have impacted the largest number of acres, ALS-resistant smooth pigweed remains a very big challenge for their vegetable industry (over 125,000 acres in the Delmarva region).

 Response:  A one-day tour was organized to provide an opportunity for EPA staff and WSSA members to discuss herbicide resistant weeds and the impact they are having on agricultural production in this region.  Twenty-seven EPA staff representing all of the divisions within the Office of Pesticide Programs participated on the tour along with 4 members representing the WSSA. The hosts of the tour were Dr. Mark VanGessel, University of Delaware, and Dr. Ron Ritter, University of Maryland. The objectives of the tour were:

  1. To demonstrate the complexity of herbicide resistant weed management.
  2. To demonstrate the severity of herbicide resistance in a variety of crops in the  Mid-Atlantic region, including vegetable crops.
  3. To discuss how farmers in the Mid-Atlantic region are dealing with the  problem, and discuss some of their constraints to management.
  4. To discuss how weed resistance has evolved to several herbicide families I  impacting all crops grown in the region.
  5. To discuss how approaches to weed management are often site and region  specific.

Four stops were included in the tour representing agricultural production and weed management issues on the Delmarva Peninsula. Stops included:

  • University of Maryland’s Wye Research Farm where the group viewed research plots evaluating weed control programs in conventional and herbicide-resistant crops
  • A commercial soybean field near the DE/MD state line where the group discussed the programs designed by the University of Delaware for management of glyphosate-resistant horseweed and the effect of environmental conditions on the success of that program
  • A commercial lima bean field near Greenwood, DE where the management of ALS-resistant smooth pigweed has become a challenge due to the limited herbicide registrations
  • A soybean field near Denton, MD that was planted with soybean rather than corn (original choice, higher income potential) because of the weed spectrum in the field.

Program Impact:  The tour participants were surveyed at the end of the tour to determine the usefulness of the tour:

  • 83 % rated the overall educational portion of the tour as very informative
  • 74% indicated that they have a better understanding of issues related to herbicide-resistance
  • 65 % indicated that they will use the information gained during the tour in their duties with EPA

For more information about the University of Delaware Extension’s Weed Science program, please visit the program’s webpage. A photo set of the tour can be viewed on the University of Delaware College of Agriculture and Natural Resources Flickr account.

Submitted by Mark VanGessel and Joanne Whalen