Italian Ryegrass Herbicide Resistance Survey and Harvest Weed Seed Control

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. There is a great potential of unidentified widespread herbicide resistance in Kentucky that needs to be investigated further. 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. Survey annual ryegrass populations from across Kentucky for herbicide resistance to pinoxaden, glyphosate, and ALS-inhibitors 2. Investigate the utility of a combine seed destructor for control of annual ryegrass in Kentucky wheat Research Methods: Objective 1: Annual ryegrass seed will be collected from wheat fields from across the state of Kentucky. Seed will be sown in the greenhouse and screened against multiple rates of glyphosate, pinoxaden, and an ALS-inhibiting herbicide. Further investigation of populations that surviving initial screen will be conducted to evaluate levels of resistance. Objective 2: Commercial fields will be evaluated for ryegrass seed retention and seed rain prior to harvest. A commercial combine will then be 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 will be evaluated. If available a seed destructor installed on a combine will also be evaluated for ryegrass seed destruction during harvest. This data will provide insight into the potential utility of such machinery in Kentucky wheat. Budget: This research is projected to cost approximately $27,500 which will include one year of salary for the graduate student who will conduct this work as well as field and greenhouse supplies, in-state travel cost, and equipment maintenance.