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Issue No. 9, Article 3/June 1, 2012

Screening Waterhemp for Glyphosate Resistance

A few weeks ago we provided an update on herbicide-resistant waterhemp populations in Illinois (issue 6, May 10). In 2011, the overwhelming majority of sampled plants and fields demonstrated resistance to one or more herbicides. With continued support from the Illinois Soybean Association, we can offer free screening of waterhemp populations for herbicide resistance again this growing season.

To submit samples, follow these directions:

  • After applying glyphosate, select five waterhemp survivors in the field.
  • Remove the top inch or two from each plant (containing young, newly emerged, healthy leaves), and seal it in a sandwich-sized zip-top plastic bag. Use a separate bag for each plant.
  • 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, but if necessary, they can be stored for a day or two in a refrigerator (but do not freeze). Do not send samples on a Friday or Saturday.
  • Print the following submission form (Adobe PDF) and complete a copy for every field sampled.

Not every waterhemp plant that survives an application of glyphosate is resistant to it. If the following conditions all apply, however, you might suspect that a waterhemp population is indeed glyphosate resistant:

  • The appropriate rate of glyphosate (plus proper adjuvants) was applied at the appropriate weed growth stage.
  • Environmental conditions during and after application were conducive for good glyphosate activity.
  • Plants that survived the glyphosate application are found next to plants that did not.
  • The field has a history of glyphosate use.

We will not charge for the screening, but please understand that we cannot promise how soon results will be available. Also, because of the way we conduct the 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, be assured that we respect the privacy of those sending samples: we will not make the exact location of any sample or name associated with them available to anyone without your permission. If you have any questions, feel free to contact Pat Tranel (217-333-1531, tranel@illinois.edu)--Pat Tranel and Aaron Hager

Pat Tranel
Aaron Hager

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