Project Overview

Reports

Commodities

• Agronomic: rye, triticale, wheat

Target Pests

• Target Pests: weeds

Practices

• Pest Management: monitoring/scouting, pesticide resistance management, pesticides

• Sustainable Communities: sustainability measures

The problem or opportunity:

Wheat is the number one cash crop in Oklahoma with a production value of  approximately 627.7 million dollars. Oklahoma planted approximately 4.3 million acres of wheat in 2022 (USDA NASS 2023), roughly one acre of wheat for every person living in the state. Weeds present major limitations to wheat producers and are barriers to progress in conservation tillage systems. Annual winter grasses like Italian ryegrass, cheat grass and wild oats are among the most troublesome wheat weeds as they compete with the crop throughout the growing season (Manuchehri et al., 2022; Peterson & Stahlman, 1995). Chemical control is one of the most prominent weed control method due to its efficiency and cost effectiveness (Derksen et al., 2002). Furthermore, no-till and conservation tillage systems have favored deployment of herbicide-tolerant crops coupled with chemical management strategies. Even though herbicides are effective for weed control in terms of production cost and benefits, over-reliance on herbicides has led to selection for grass weeds, i.e., those with similar phenological development to wheat, and evolution of herbicide-resistant weeds. In the United States, 86 unique cases of herbicide resistant wheat weeds have been reported to date (Heap I, 2023). Wheat weeds from different US states have developed resistance to various modes of action including WSSA Group 1 (ACCase inhibitors), 2 (ALS inhibitors), 3 (Root growth inhibitors), 4 (Auxin mimics), 9 (EPSP synthase inhibitors) and Group 15 (Very long chain fatty acid inhibitors) (Heap I, 2023). In Oklahoma, the first case of herbicide resistance wheat weed was reported in Kochia species in 1992. The species was resistant to Group 2 mode of action. After that, herbicide resistance in Oklahoma wheat weeds have been severely under reported and the extent of herbicide resistance is not well documented. This is demonstrated by the lack of reporting from Oklahoma compared with neighboring states in the International Herbicide-Resistant Weed Database (Heap I, 2023), paired with anecdotal reports of undocumented herbicide resistance from previous and current Oklahoma state weed scientists and extension specialists.

Approach:

Knowing the distribution of troublesome grass weeds and prevalence of herbicide resistance in these species is one of the fundamental steps in development of integrated weed control and resistance management strategies in wheat and small grains. However, the current science-based knowledge of the distribution of grass weeds and prevalence of herbicide resistance in Oklahoma wheat fields is inadequate to the best of our knowledge. In response to these knowledge gaps, this study aims to conduct scientific surveys of major wheat fields in Oklahoma and understand the distribution of grass weeds and herbicide resistant weed populations.

Anticipated impact:

The long-term impact of this study will provide updated best management practices for controlling problematic grasses in Oklahoma wheat. The short-term outcome of this study will involve quantifying which herbicides are less effective due to resistance within target weed populations. The best management practices and knowledge of resistance will enable growers to make more informed decisions around chemical weed management in wheat and small grains. This knowledge will drive behavioral shifts to avoid over-reliance on specific herbicides, use alternative herbicides if available and adopt integrated weed control strategies. Additionally, this project will promote awareness and trust between university staff and members of the largest commodity group in Oklahoma, increasing the likelihood for sustained funding and cooperation for future research endeavors.

1. Identification of most problematic grass weeds in Oklahoma wheat fields.  
2. Determine the degree and extent of herbicide resistance across grass weeds in Oklahoma.
3. Report findings and update chemical control best management practices.