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Issue No. 18, Article 2/August 6, 2010

Screening Waterhemp for Glyphosate Resistance

In the July 2 issue of the Bulletin, we announced that we would accept samples of waterhemp from Illinois for herbicide-resistance screening using molecular biology assays. Several recent inquiries suggest that interest among producers remains high. Please observe the following procedures to submit samples:

  • Select five waterhemp survivors in the field.
  • Remove the top inch or two from each plant--with young, newly emerged, healthy leaves--and seal it inside in a sandwich-sized plastic zippered bag. Use a separate bag for each plant.
  • Place the bags in an envelope and send by overnight delivery to 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. Please do not drop off samples for herbicide-resistance screening at the Plant Clinic.
  • Include with the samples your contact information, any details about the herbicide 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).

Please keep in mind the following combination of conditions that might lead you to suspect a waterhemp population of being resistant to glyphosate:

  • 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 were controlled.
  • The field has a history of glyphosate use.

We will not charge you for the screening service, but please understand that we cannot promise how soon results will be available. We also point out 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.

If you have any questions, feel free to contact either of us (tranel@illinois.edu, 217-333-1531; hager@illinois.edu, 217-333-4424).--Pat Tranel and Aaron Hager

Pat Tranel
Aaron Hager

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