Updated January 5, 2024:
Project Title: Sampling Program to Screen for Herbicide Resistance in ND Weeds
Principal Investigator: Zack Bateson (NAGC)
Co-Investigators: Joseph Ikley (NDSU), Quincy Law (NDSU), Brian Jenks (NDSU), Michael Christoffers (NDSU), Missy Berry (NAGC), and Megan O’Neil (NAGC)
Research Overview:
Herbicides have been essential in weed control for the last 70 years. However, widespread use has allowed many weed species to evolve resistance to multiple classes of herbicides. The rapid spread of herbicide resistance (HR) has motivated researchers to find mutations in the target sites associated with resistance. As target-site mutations become known, rapid DNA-based tests can be created to search for these mutations in other weed populations and species. This project makes DNA-based tests accessible to soybean growers to screen for HR pigweeds and kochia across North Dakota. The National Agricultural Genotyping Center (NAGC) has partnered with weed scientists from North Dakota State University to launch a new statewide sampling program to evaluate the distribution of specific mutations that result in resistance to Group 2, 9, and 14 herbicides in pigweeds. The project also provided initial funds to validate new screening tests for HR in kochia. We have distributed mail-in kits across North Dakota for participants to collect and ship leaves for DNA testing at NAGC. Confidential results are provided to participants that are useful for discussions for in-season and future weed control strategies. Lastly, compiled results are used to create a county-level map that highlights herbicide resistance issues across the state.
Objectives:
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.
Completed Work: Deliverables and/or Milestones:
In August and September, we distributed 400 collection kits across North Dakota (Objective 1). Kits were shipped primarily to county extension offices for pickup, but several agronomists and farmers received kits directly. Each sampling kit consisted of one large pre-paid envelope containing four smaller envelopes to collect leaf samples from three pigweeds and one kochia. All participants have received HR results (Groups 2, 9, and 14) for pigweed samples submitted to NAGC. The kochia samples submitted remain in storage until DNA tests have been validated.
Progress of Work and Results to Date:
Submitted Samples - In the first three months of the sampling program, 34 collection kits have been returned to NAGC. In total, NAGC has received 61 pigweed and 50 kochia samples from 24 counties in North Dakota (Fig.1).
The pigweed samples originated from 17 counties and were tested at three DNA markers linked to resistance to ALS-inhibitors (Group 2), EPSPS-inhibitors (Group 9), and PPO-inhibitors (Group 14). We found 59% (10/17) of the surveyed counties had pigweed samples with genetic markers associated with HR (Fig. 2; Objective 2).
Kochia HR tests – We have ordered the necessary diagnostic reagents to explore DNA-based tests for known mutations associated with resistance to Groups 2, 4, 9, and 14 herbicides. Most of the work to date has focused on a test to detect resistance to PPO-inhibitors (Group 14). So far, we have a series of positive controls from North Dakota kochia populations with known resistance to PPO-inhibitors as well as a very promising assay to detect two distinct mutations recently discovered.
Work to be Completed:
Collection kits – We will create 100 - 200 more collection kits prior to spring planting season (Objective 1). These kits will be distributed to county extension offices and given to anyone who may request kits during the winter meetings and conventions.
Reporting and Maps – We will test and report HR results on pigweed samples that are shipped to NAGC by mid-June 2024 (Objective 2). Reports are usually released in less than 10 days from arrival to NAGC. An updated county-level map will be created in June that contains results from new submissions.
Kochia HR Test – We will continue to develop and validate new HR tests in kochia (Objective 3). Currently, we are working to obtain known positive controls for kochia resistant to Groups 2, 4, and 9 herbicides from researchers that have previously published their HR tests for kochia. Once positive controls are found and assays are validated, we will provide HR results to those that submitted kochia to NAGC.
Other relevant information: potential barriers to achieving objectives, risk mitigation strategies, or breakthroughs: The success and future growth of the sampling program is contingent on Ag professionals’ willingness to collect leaf samples across the state. While we have had relatively few kits returned (8.5% return rate), we anticipate that collection will be at its greatest during the second half of the project period. HR screening results are more useful early in the planting season when shifts in weed control strategies may still be possible. Thus, we plan to continue advertising the sampling program to reach our quota of free tests to North Dakota soybean growers.
Summary: Weed populations are evolving resistance to an increasing number of herbicides. There is an HR crisis and new surveillance tools are needed to describe the distribution of HR weed populations across the landscape. NAGC and NDSU scientists have organized a sampling program to detect potential HR weeds using DNA-based tests. So far, we have released 24 individual reports to participants that collected a total of 61 pigweeds. The preliminary maps provide a broader view of where possible HR hotspots occur in the state. As the sampling program continues, we hope results will help growers develop more effective weed control strategies.
View uploaded report 