Italian Ryegrass Herbicide Resistance Survey and Harvest Weed Seed Control - Year 2

21-22 KySGGA Executive Research Proposal Summary Italian Ryegrass Herbicide Resistance Screen and Harvest Weed Seed Control – Year 2 Travis Legleiter - Assistant Extension Professor: Weed Science Justification: Italian ryegrass (annual ryegrass) continues to be problematic in Kentucky wheat acres and has shown rapid increases in infestations over the past two growing seasons. This weed species has proved to be the most problematic weed for Kentucky wheat growers with our previous research identifying at least one population of glyphosate-resistant and one population of pinoxaden (Axial XL) resistant annual ryegrass in Kentucky wheat fields. Since the identification of the single population of pinoxaden resistant ryegrass from Simpson County in 2017, we have observed numerous fields through the state with late season ryegrass escapes. In addition to those escapes we have also received multiple complaints of failed glyphosate burndowns of this weed. The number of complaints of failed burndowns increased exponentially in 2021. Herbicide resistance in ryegrass is inevitable and Kentucky wheat acres are on the brink of widespread herbicide resistance. The lack of potential postemergence herbicides and limits of currently effective preemergence herbicides call for additional control tactics such as seed destruction at harvest. Rigid ryegrass seed destruction at harvest has been implemented by Australian farmers for over a decade with much success. The investigation of the potential of this technology in Kentucky wheat acres is warranted at this time as Kentucky wheat farmer continue to struggle with annul ryegrass and herbicide resistance. Objectives: 1. Conduct dose response studies on ryegrass populations that showed lack of control initial greenhouse screenings 2. Continue to investigate ryegrass seed retention, seed rain, and combine dispersal to further understand the utility of harvest weed seed control Research Methods: Objective 1: 22 populations of Italian ryegrass were screened against a susceptible population of ryegrass in 2020/21 using glyphosate, pinoxaden, and pinoxaden plus fenoxaprop. At least two populations had significantly lower control using glyphosate and at least seven had significantly lower control with pinoxaden as compared to the susceptible population. The suspect populations will be further screened using dose response techniques to further quantify potential herbicide resistance within the populations. Objective 2: Ryegrass seed retention and seed rain samples were collected prior to the 2021 wheat harvest. A commercial combine was also used to harvest wheat and ryegrass seed shatter at the combine head, seed dispersal through the back of the combine, and ryegrass seed contamination in the grain tank were collected. The samples will be processed in the fall and winter of 2021/22. This data will provide insight into the potential utility of harvest weed seed control in Kentucky wheat. Budget: This research is projected to cost approximately $17,663 which will include salary for Amber Herman (graduate student) who is conducting this work as well as field and greenhouse supplies.