North Dakota farmers and agriculture professionals report new cases of weeds overcoming herbicides each year. As herbicide resistance (HR) continues to spread, identifying where and what HR traits are lurking in local weed populations can inform control strategies. Genetic testing is a newer method to rapidly screen for HR in field-collected weed samples, which reduces the demands on greenhouse trials that are often limited by space, time, and funding. Last year, our collaborative project used both greenhouse trials and genetic testing to investigate HR in pigweeds collected from 16 counties in North Dakota. We confirmed widespread resistance to imazamox (Group 2) and glyphosate (Group 9), but a patchy distribution of resistant weed populations to fomesafen (Group 14). Importantly, genetic testing for markers associated with resistance to glyphosate and fomesafen strongly agreed with the greenhouse work in both waterhemp and Palmer amaranth. Here, we propose to expand this survey by 1) piloting a farmer- and agronomist-driven sampling program, and 2) validating genetic tests in kochia to include in future surveys. This new program answers the call for increased awareness to the growing HR crisis and offers new diagnostic technologies for farmers to identify the HR potential of weeds in their fields.

1. Increase genetic screening for herbicide resistance in pigweeds by distributing pre-labeled envelopes and cover testing fees.
2. Generate distribution map showing counties where genetic tests indicate possible pigweed resistance to specific groups of herbicides.
3. Develop genetic screening tests for herbicide resistance in kochia to add to the sampling program.

1. North Dakota submitters will receive electronic, personalized reports with the HR results from pigweed samples they collected.
2. County-level maps showing where HR genotypes were located.
3. Up to three genetic tests for HR screening in kochia for future use in the program.

Our proposed weed sampling program will be the first in North Dakota where collection is farmer-driven and supported by multiple commodity groups. The annual program will provide farmers a unique opportunity to test both existing and newly discovered populations in their fields. Collection can be performed at any time during the growing season, including before or after the timing of herbicide applications. Genetic results will help participating farmers improve their current herbicide practices. For instance, if particular HR traits are detected by genetic testing, then farmers can tailor herbicide mixes to provide the maximum return, potentially on a field-to-field basis. The statewide map will show county-level hotspots to share with the agriculture community, and provide clarity on where more resources, such as extension and outreach, are needed to combat HR weeds in North Dakota.