No. 10 Article 2/June 10, 2011

Screening Waterhemp for Glyphosate Resistance

Earlier this season we provided an update on the occurrence of herbicide-resistant waterhemp populations in Illinois (issue 3, "Herbicide-Resistant Weeds in Illinois: A Cause for Concern"). Much of the data we presented was generated by using molecular biology techniques to screen waterhemp samples submitted from across Illinois.

Waterhemp plants, dead and alive.

During the 2011 growing season, with funding provided by the Illinois Soybean Association, we can again offer free screening of waterhemp populations for herbicide resistance. If you have a waterhemp population that you suspect is resistant to glyphosate, please consider sending us samples and we will test for resistance not only to glyphosate, but also to the PPO and ALS inhibitors.

Details for sampling are as follows:

  1. Following application of glyphosate, select five waterhemp survivors in the field.
  2. Remove the top inch or two (containing young, newly emerged, healthy leaves) from each plant and seal it inside in a sandwich-sized plastic zipper bag. Use a separate bag for each plant.
  3. Place the bags in an envelope and send by overnight delivery to Dr. Chance Riggins, 320 ERML, 1201 W. Gregory Dr., Urbana, IL 61801. Ideally, samples should be sent the same day they are collected. If necessary, however, they can be stored for a day or two in a refrigerator (but do not freeze) until shipped.
  4. Include with the samples your contact information, any details about the herbicide use history in the field, and the location of the field (GPS coordinates if possible; at a minimum indicate the county where the field is located).

Not every waterhemp plant that survives an application of glyphosate is resistant to it, but the following four factors, in combination, might lead you to suspect that a waterhemp population is indeed glyphosate-resistant:

We will not charge you for the testing service, but please understand that we cannot promise how soon results will be available. Also be aware that because of the way we conduct our resistance tests, a result of "sensitive" does not rule out the possibility that the plant actually is resistant, but by a mechanism different from what we are testing for.

Finally, we assure you that we respect the privacy of those sending samples: we will not make the exact location of any samples, or names associated with them, available to anyone without permission. If you have questions, feel free to contact Pat Tranel (217-333-1531; Tranel and Aaron Hager

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