Updated February 1, 2021:
Current agriculture systems are compromised by the evolution of glyphosate-resistant weeds. Over 30 species have evolved resistance to glyphosate worldwide and 15 of these are found in the U.S. Nine of these glyphosate-resistant biotypes are major threats to soybean production because they are resistant to more than one herbicide site of action. No new herbicide sites of action have been introduced since the early 1990’s. However, industry has introduced herbicide resistance traits into soybean that allow the use of corn herbicides in soybean, which will offer short term help with controlling herbicide-resistant weeds. Many people were concerned that the introduction and widespread use of the dicamba and 2,4-D resistance traits and the concomitant use of the herbicides will result in off-target movement of the herbicides to sensitive crops, landscape plants, nurseries, and trees. Data from state pesticide regulatory agencies fully support the off-site movement concerns with dicamba (Xtend soybean) and there is much work to be done by industry and applicators to reduce incidences of off-target movement. Enlist (2,4-D resistant) soybeans will be launched in 2019 and there are similar concerns with off-target movement because of the time of the year when 2,4-D herbicide will be used postemergence in soybean. In the near future, soybean varieties with resistance to glyphosate, glufosinate and either group 27 herbicides, dicamba, or 2,4-D will be commercially available. This will undoubtedly speed the evolution of weeds resistant to multiple sites of action.
Despite documented evidence of higher grower awareness of herbicide-resistant weeds, the number of herbicide-resistant weeds continues to grow, and areas infested are increasing at an alarming rate. There continues to be a need for grower and retailer education about the impact of herbicide-resistant weeds, how to manage these problems, how to diversify weed management, and how to properly use the new herbicide resistance traits to slow the inevitable evolution of weeds resistant to the herbicides that will be used in the new technology.
This multi-state project was started 6 years ago to inform growers about best management practices for new soybean herbicide resistance traits. Because there was a greater need for information to control herbicide resistant weeds in the early years of this effort, and there were delays in trait regulatory approvals, most of the early work focused on workshops and development of training materials for control of herbicide-resistant weeds in Roundup Ready and non-GMO soybeans. More recently, utilization of Liberty Link and Xtend soybean has grown, cover crop adoption has expanded, thus, the emphasis has shifted towards education and demonstration using these technologies to control weeds. However, there is still a need to continue the education and demonstration process as we learn more about application technologies to keep herbicides from moving off-target, use of diverse cover crops as a weed control tool, and with the recent approval of Enlist soybean and additional herbicide-resistance traited soybean varieties which will be grown commercially in the near future.