Do you think you have a resistant waterhemp population? If so, send your waterhemp samples to the University of Illinois for a free screening. The Illinois Soybean Association is providing funding for the 2011 growing season to test Illinois waterhemp samples for resistance to glyphosate, PPO inhibitors and ALS inhibitors.
Aaron Hager, University of Illinois Extension weed specialist, says just because a waterhemp plant survives following an application of glyphosate does not mean it's resistant to glyphosate. He offers a few points to help growers recognize glyphosate resistant populations.
1. The appropriate rate of glyphosate (plus proper adjuvants) was applied at the appropriate weed growth stage.
2. Environmental conditions during and after application were conducive for good glyphosate activity.
3. Plants that survived following the glyphosate application are found next to plants that were controlled.
4. The field has a history of glyphosate use.
U of I professor of weed science Pat Tranel says waterhemp samples should be collected following application of glyphosate. He recommends selecting five survivors in the field after the glyphosate application. Then, remove the top inch or two (containing young, newly emerged, healthy leaves) from each plant and seal inside a sandwich-sized Ziploc bag. Each plant must be enclosed in a separate bag.
Then, 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, Tranel adds. If necessary, they can be stored for a day or two in a refrigerator (but do not freeze) until shipped.
Be sure to include 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 in which county the field is located) with the samples.
This is a free service. However, turnaround time cannot be guaranteed. Because of the way in which U of I conducts the resistance tests, a test result of "sensitive" does not rule out the possibility that the plant actually is resistant, but by a mechanism that is different than what they are testing. Privacy will be respected of those sending samples – the exact location of samples, or names associated with samples, will not be made available to anyone without the grower's permission.
For more information about weeds and other crop-related information, read The Bulletin at http://bulletin.ipm.illinois.edu.