Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2006
Publication Date: 1/1/2007
Citation: Henry, W.B., Shaner, D.L., West, M.S. 2007. Shikimate accumulation in sunflower, wheat, and proso millet after glyphosate application. Weed Science 55:1-5. Interpretive Summary: In this manuscript we describe the various effects of herbicide application on three crops grown in the Central Great Plains, sunflower, proso millet and wheat. Roundup is one of the most commonly used herbicides throughout the world. Because it is so widely used under so many different environmental conditions, this herbicide could be misapplied or drift onto neighboring crops. Because organic producers are wary of any herbicide exposure on their crops and conventional producers with non-roundup ready crops could be subject to herbicide injury from roundup drift, it would be good to be able to identify crops that had been exposed to roundup. The objective of our research was to examine a test that is useful for identifying crops that have been sprayed with roundup. We found that we could identify a peak in plant response to roundup application between 4 and 7 days following herbicide exposure. In summary, further refinement of this procedure may lead to an assay that can detect roundup drift or roundup resistant weeds.
Technical Abstract: Experiments were conducted to examine the utility of a spectrophometric leaf disc assay for detecting shikimate accumulation following glyphosate application in sunflower, proso millet, and wheat. The assay was conducted on both greenhouse and field grown plants. Glyphosate was applied at five rates ranging from 840 kg ae ha-1 to 53 kg ha-1. Shikimate accumulation data were generated at 1, 4, 7, and 14 days following application. Sunflower accumulated shikimate more rapidly and at lower glyphosate application rates than the other two species. At 14 DAA, the two highest glyphosate rates remained detectable in all three species. Plants receiving lower rates (210, 105, and 53 g ha-1) of glyphosate had begun to grow out of the injury or at least the excess shikimate remaining in the plants was not greater than that present in untreated controls. This spectrophotometric assay is both rapid and simple, with respect to other means of detecting shikimate, and it can be used to detect glyphosate drift. In summary, for this assay to be used by crop managers, samples from potentially drift affected crops should be taken as soon as possible following the suspected drift event or immediately after the appearance of glyphosate injury.