Weeds are a major production concern for soybean producers throughout the state of Oklahoma. Weeds compete with the soybean crop for sunlight, moisture, and nutrients throughout the growing season. Weed management programs are based on the weed species present, however, other factors such as soil type, pH, organic matter, and rotational crops must all be considered when making a herbicide recommendation.

The introduction of Roundup-Ready technology revolutionized weed control in many crops including soybean. Due to the relative effectiveness and simplicity this system led many growers to rely solely on glyphosate as the only herbicide used in their soybean production system. Herbicide resistance to glyphosate has reduced the effectiveness of this system for many growers. Many Oklahoma growers also deal with acetolactate synthase (ALS) resistance. Due to this fact there has been a heavy reliance on protoporphyrinogen oxidase inhibitor (PPO) herbicides to control these weeds. Recently, there has been anecdotal evidence that there may be PPO resistance in Oklahoma. Therefore, other weed management systems and combinations of multiple mode-of-action herbicide programs must be evaluated to determine systems that are both efficacious and economical.

This research falls under the Production Priority Area regarding production systems to reduce cost, increase yields and suppress weeds. It also addresses one of the high priority areas: Glyphosate Resistant Weeds.

This research will focus on weed management practices to most effectively and economically control weeds. Studies will be conducted to investigate the use of residual weed management systems. These will include both preemergence and postemergence residual herbicides used in conjunction with glyphosate, glufosinate, dicamba, and 2, 4-D. Conventional weed management systems will also be investigated evaluating preemergence and postemergence herbicides. Weed management technologies (depending on seed availability) will include Balance GT (tolerance to isoxaflutole, glyphosate, glufosinate), Liberty-Link (tolerance to glufosinate), Roundup Ready Xtend (tolerance to glyphosate and dicamba), Enlist (tolerance to 2, 4-D, glyphosate, glufosinate), HT3 (tolerance to glyphosate, glufosinate, and dicamba) depending on seed availability will be investigated. These studies will not only look at developing weed management systems that will most effectively control weeds but also systems to protect the future utility of this technology. Primary soybean research has been conducted at the Oklahoma Experiment Stations near Bixby on a known glyphosate resistant location for several years. Additional studies have been conducted at Chickasha, Fort Cobb, and Lane.

Information from these studies will be used in extension presentations, publications, and other educational events. Dicamba trainings were conducted throughout the state in 2018 and 2019 with additional support in 2020. Efforts will also include updating of extension soybean publications.

Research projects will be developed in 2020 to further develop knowledge on new and existing technologies for weed control in soybean. Weed management is an ever-evolving issue in soybean production. Weed management projects will be continued in future years as well.