New genetic test provides rapid confirmation of herbicide-resistant kochia and pigweeds

Herbicide-resistant kochia is problematic for farmers in North Dakota, says Joe Ikley, North Dakota State University Extension weed specialist.

NDSU weed scientists first confirmed resistance to PPO-inhibiting (Group 14) herbicides in kochia in 2022. In a collaborative effort, BASF scientists discovered a target-site mutation in kochia that provided resistance to Group 14 herbicides. Once the target-site was identified, the National Agricultural Genotyping Center (NAGC), located on NDSU’s campus, developed a rapid test to detect the mutation from DNA extracted from leaves.

″We are happy to announce that this DNA-based test is now available for public submissions of kochia samples,″ shares Ikley.

In addition to testing for Group 14 resistance in kochia, the NAGC offers DNA tests for resistance to Group 14 herbicides in waterhemp and Palmer amaranth, as well as Glyphosate (Group 9) and ALS-inhibitors (Group 2) in kochia, waterhemp and Palmer amaranth. The NAGC can also test for Group 2 resistance in any pigweed species.

Standard turnaround time for results will be 7 days from arrival at NAGC.

Thanks to sponsorships from the North Dakota Corn Utilization Council, North Dakota Soybean Council, North Dakota Specialty Crop Block Grant and Minor Crop Utilization Grants, funding is available to test the first 1,000 North Dakota pigweed or kochia samples for no charge.

Each NDSU Extension county office will have testing kits on hand with instructions on how to collect and send samples. Once kits run out at county offices, samples can be submitted following the self-mailing instructions and submission form at https://genotypingcenter.com/product/kochia/.

Free testing is currently limited to four samples per farming operation. For additional tests, as well as samples originating from outside of North Dakota, refer to the NAGC website for charges. Please use the non-North Dakota submission form provided on the website.

To get the most impactful information from these DNA tests, leaves should be collected from plants that survive the herbicide in question. The application will remove susceptible plants and increase confidence of the resistance determination.

Individual sample results will remain confidential. Test results will be sent directly from the NAGC to the e-mail provided on the submission form. The NAGC will aggregate results to provide data at the county-level, but no individual information will be released.

The sampling program using DNA testing began in the Fall of 2023. To date, the NAGC has received 51 kochia samples from 21 counties in North Dakota.

Results found 33% of samples contained a mutation that confers resistance to Group 14 herbicides, 82% of samples contained a mutation that confers resistance to glyphosate and 51% of samples contained mutations that confer resistance to Group 2 herbicides.

″It is important to note that DNA testing can only detect known target-site mutations that confer resistance,″ says Ikley. ″There could be unknown mutations, or other mechanisms of resistance that these tests cannot detect.″

To collect a sample for testing:

1. Locate pigweeds or kochia in the field. Proper ID is important before collecting leaf samples.

2. Collect two leaves near the top of the plant (leaves must be larger than a standard hole-punch to allow for adequate DNA extraction). Place two (2) leaves from a single plant into one (1) zipper bag or small envelope. Do not mix leaves from multiple plants.

3. With a marker, label the outside of the collection bag with a unique Sample ID. The Sample ID can be in the following format: Year-Month-County-Personal Field ID (Example: 24-05-Cass-SE4). Make sure to also write the Sample ID on the submission form.

4. Sample additional weeds in fields of your choice by following Steps 1 to 3. Send a maximum of four (4) total plants for testing. Keep samples dry and at room temperature before shipping.

5. Mail the submission form and individually-packaged samples in a large business envelope to: National Ag Genotyping Center, 1616 Albrecht Boulevard North, Fargo, North Dakota, 58102.