Soil moisture and texture effects on herbicide resistance expression in italian ryegrass (Lolium perenne ssp. multiflorum)

Authors: AHLERSMEYER, ANDREW - Auburn University; Price, Andrew; MAITY, ANIRUDDHA - Auburn University

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/21/2025
Publication Date: 2/24/2025
Citation: Ahlersmeyer, A., Price, A.J., Maity, A. 2025. Soil moisture and texture effects on herbicide resistance expression in italian ryegrass (Lolium perenne ssp. multiflorum) [abstract]. Weed Science Society of America, Vancouver, BC February 24-27 2025.

Interpretive Summary:

Technical Abstract: Italian ryegrass is a winter annual grass weed that causes significant issues for corn, soybean, wheat, and small grain production in Alabama. Recent studies have documented resistance to glyphosate, ALS-, and ACCase-inhibitors throughout the southeastern U.S., and reduced control of Italian ryegrass is likely to be exacerbated by various climatic factors. The objective of this study was to document the effects of altered soil textures and moistures on Italian ryegrass growth and development following applications of glyphosate and pinoxaden. A greenhouse trial was conducted in 2024, in which seeds of a suspected-resistant Italian ryegrass population were planted in pots containing field soil. The three soil types used included a loamy sand, silt loam, and clay, representing three unique agricultural production regions of Alabama. Laboratory calibration methods were used to determine the average water holding capacity of each soil, and pots were irrigated daily at 10%, 20%, and 40% of each soil’s water holding capacity to maintain constant moisture regimes (low, medium, and high, respectively). Labeled rates of glyphosate and pinoxaden were applied each pot, and various physiological measurements (injury, mortality, plant height, seed head production) were recorded thereafter. Neither glyphosate nor pinoxaden completely controlled Italian ryegrass, highlighting the significant presence of multiple-resistant Italian ryegrass in Alabama. However, varying soil moistures and textures had fascinating impacts on control using these foliar-applied, systemic products. For both herbicides, greatest injury was noted at low soil moisture levels. Control using glyphosate was significantly higher in the clay soil compared to the loamy sand and silt loam, but this trend reversed for pinoxaden. For plant height and seed head production, plants exposed to either no herbicide or pinoxaden responded as expected, i.e., taller plants and more seed heads with increased moisture and finer soil texture. However, glyphosate-treated plants grew the tallest and produced the most seed heads in clay soil under low moisture. Interestingly, these are the same conditions in which we noted highest visual control. These preliminary findings warrant replications of this research in 2025. Ultimately, we believe that these data will provide vital information to farmers and stakeholders in Alabama and the southeastern U.S.