Submitted to: Western Society of Weed Science Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/5/2003
Publication Date: 4/6/2003
Citation: Molin, W.T., Vaughn, K.C., Hirase, K. 2003. Engame causes cotyledon and leaf surface lesions and collapse of sub-epidermal tissues of glyphosate-sensitive species. Western Society of Weed Science Meeting Proceedings 45:123-124. Interpretive Summary:
Technical Abstract: The efficacies of Roundup UltraMax and Engame formulations of glyphosate were compared for control of velvetleaf (Abutilon theophrasti Medik.), hemp sesbania (Sesbania exaltata (Raf.) Rybd. ex A. W. Hill), barnyardgrass (Echinochloa crus-galli (L.) Beauv.), and yellow nutsedge (Cyperus esculentus L.). Estimates of the I50 for inhibition of growth decreased with time and stabilized at about three WAT. The I50 for the Engame formulation was 2- to 4-times lower than Roundup UltraMax for each of the weed species. Engame was also evaluated on Roundup Ready® cotton and soybean, and injury was transient and did not exceed 20%. Cotyledon and leaf surface injury on cotton was observed within one hour after application of the Engame formulation, but no perturbations were observed with the Roundup UltraMax formulation. Scanning electron microscopy of the glyphosate-sensitive cotton cotyledons following Engame treatment showed that cuticular waxes were perturbed resulting in the formation of cuticular pits. AMADS (1-aminomethanamide dihydrogen tetraoxosulfate), a proprietary mixture of urea and sulfuric acid used in the Engame formulation, did not cause cuticle perturbations unless applied with a surfactant. Transmission electron microscopy of Engame-treated leaves showed catastrophic cell death beneath the cuticular pits. Perturbations of the cuticular waxes, rapid uptake and cell death may account for the greater efficacy of the Engame formulation of glyphosate.