2016 University of Illinois Plant Clinic Herbicide Resistance Report

Glyphosate and PPO inhibitor Summary: 593 field samples representing approximately 2,000 waterhemp or palmer amaranth plants were tested for herbicide resistance at the University of Illinois Plant Clinic in the 2016 season. The Plant Clinic started offering herbicide resistance testing of waterhemp for resistance to two groups of herbicides (glyphosate and PPO inhibitors) in 2015. We added palmer amaranth testing in 2016.  Almost twice as many whole fields were tested 2016 compared to last year, 593 vs. 338.  The tests use qPCR protocols to determine if the most common site of action for resistance to these two groups of herbicide is present in the plants.

Samples from 10 states across the Midwest were submitted in 2016. The following chart details the number of field samples from each state, along with the number of fields that were positive for glyphosate resistance and PPO inhibitor resistance.  Fields with plants that are positive for both glyphosate and PPO inhibitor resistance are of particular concern due to the limited possibilities for control of these weeds.

2016 University of Illinois Plant Clinic Herbicide resistance testing results.
State No. of Field samples No. of Glyphosate resistant fields No. of PPO Inhibitor resistant fields No. of Fields Positive for both Glyphosate and PPO Inhibitor resistance % of Fields Positive for both Glyphosate and PPO Inhibitor resistance  
IL 378 280 244 182 48.1 %
IA 87 77 70 65 74.7 %
IN 9 9 6 6 66.6 %
KS 1 1 0 0 0 %
KY 3 1 1 0 0 %
MI 1 0 1 0 0 %
MN 78 58 34 27 34.6 %
MO 11 10 10 9 81.8 %
NE 8 5 1 0 0 %
WI 17 15 4 2 11.8 %
 

In Illinois, we received samples from 52 counties that had at least one sampled field that had waterhemp or palmer amaranth plants that tested resistant to both glyphosate and PPO inhibitors.

 

Palmer amaranth issues: Until the 2016 season, palmer amaranth in Illinois was not known to be resistant to PPO inhibitors.  However, several samples from southwestern Illinois were confirmed to be PPO inhibitor resistant (3 from Madison,  and 1 from St. Clair counties) in our testing.

Due to difficulties in positively identifying related amaranth species, and concern regarding possible contamination of seed with amaranth weed seeds including palmer amaranth, the Plant Clinic is now offering a molecular identification service to positively identify palmer amaranth. This protocol was adapted and tested in fall of 2016, and will be offered to the public starting in 2017.   Find our sample forms for this testing on the Plant Clinic website.

Authors: Diane Plewa and Suzanne Bissonnette


Herbicide Resistance in Waterhemp: PPO inhibitor and Glyphosate Testing University of Illinois Plant Clinic 2016

What is your waterhemp doing ? Waterhemp glyphosate and PPO inhibitor resistance testing was offered by the Plant Clinic for the first time in 2015. Due to the strong demand for this testing, we are offering it again this year. We adapted protocols developed by Dr. Tranel’s lab in the Dept. of Crop Sciences to transition the molecular protocols for glyphosate and for PPO Inhibitor resistance from a research laboratory to a service lab offering. In 2015, we screened plants from 338 fields (approx. 1350 plants) in 5 states, including 240 fields from Illinois. To the best of our knowledge, we are the only Plant Clinic in the country offering this service.

The data  generated showed that the majority of the fields sampled contained waterhemp resistant to at least one of these two classes of herbicides. The Plant Clinic was sponsored by the Regional Crop Management Extension Conferences to purchase some of the necessary equipment for this endeavor.

2015 Counties with waterhemp samples testing positive for PPO inhibitor or glyphosate resistance, University of Illinois Plant Clinic.

2015 Counties with waterhemp samples testing positive for PPO inhibitor or glyphosate resistance, University of Illinois Plant Clinic.

To submit waterhemp samples for testing: After applying herbicide, select up to 5 waterhemp survivors. Remove the top inch or two from each plant (containing young, newly-emerged, healthy leaves. Older leaves and leaves that are damaged by herbicide will be more difficult for us to work with), and seal it in a sandwich-sized tip-top plastic bag. Use a separate bag for each plant. Place the bags in an envelope and send via overnight delivery to the University of Illinois Plant Clinic, along with a Waterhemp Testing sample submission form (see below). Ideally samples should be sent the same day they’re collected, but if necessary they can be stored for a day or two in a refrigerator. Do not freeze the samples. Do not send samples on Friday or Saturday.

Select top few inches from the waterhemp  for testing

Select top few inches from the waterhemp for testing

Sample submission forms are available for download on our website: http://web.extension.illinois.edu/plantclinic/downloads/WaterhempForm.pdf Fill out a new form for each field. There is a $50 fee for the testing, which includes both the glyphosate and PPO-inhibitor resistance tests. Authors: Suzanne Bissonnette and Diane Plewa