Shikimate Accumulation in Sunflower, Wheat, and Proso Millet after Glyphosate Application

Experiments were conducted to examine the utility of a spectrophometric leaf disc assay for detecting shikimate accumulation after glyphosate application in sunflower, proso millet, and wheat. The assay was conducted on both greenhouseand field-grown plants. Glyphosate was applied at five rates ranging from 840 to 53 g ae ha. Shikimate accumulation data were generated at 1, 4, 7, and 14 d after application (DAA). Sunflower accumulated shikimate more rapidly and at lower glyphosate rates than the other two species. At 14 DAA, glyphosate at the two highest rates remained detectable in all three species. Plants receiving lower glyphosate doses (210, 105, and 53 g ae ha) had begun to grow out of the injury, or at least the shikimate levels in the plants were no longer significantly different than that present in the 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. For it to be used by crop managers, samples from potentially driftaffected crops should be taken as soon as possible after the suspected drift event or immediately after the appearance of glyphosate injury. Nomenclature: Glyphosate; proso millet, Panicum miliaceum L. ‘Sunup’; sunflower, Helianthus annus L. ‘Triumph 765C’; wheat, Triticum aestivum, L. ‘Stak-Tite N25550’.