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ARS Home » Southeast Area » Auburn, Alabama » Soil Dynamics Research » Research » Publications at this Location » Publication #303061

Title: Bioassay techniques for detecting root leakage of auxinic herbicides

item PARKER, E - Auburn University
item MCELROY, J - Auburn University
item WEHTJE, G - Auburn University
item Price, Andrew

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2014
Publication Date: 2/28/2014
Citation: Parker, E.T., Mcelroy, J.S., Wehtje, G.R., Price, A.J. 2014. Bioassay techniques for detecting root leakage of auxinic herbicides. Southern Weed Science Society. CDROM.

Interpretive Summary:

Technical Abstract: Biological assay (bioassay) techniques are a simple way to determine the presence of herbicides in soil or other potting media. Understanding the fate of herbicides after absorption is important when guidelines for use are developed. Greenhouse studies were conducted with the herbicide aminocyclopyrachlor (ACPC), a hormone disrupting herbicide that exhibits selective broadleaf weed control in tolerant graminaceous species, to determine if root exudation occurs when applied at labeled rates. ACPC was compared with dicamba, another synthetic auxin herbicide known to exude from plant roots, and against a non-treated check. Bioassay studies were conducted utilizing four graminaceous species including bahiagrass, bermudagrass, cogongrass, and tall fescue as target species with cucumber representing the sensitive species. Herbicide treatments were applied only to the grass foliage by placing small plastic cups over each sensitive plant; the soil was then covered with 2 cm of perlite and finally the pots were treated with a standard application rate of dicamba (2.24 kg ai ha-1) or ACPC (0.21 kg ai ha-1) using an enclosed spray chamber. In the second study plants were established in individual hydroponic boxes with an aerated nutrient solution. Treatments were applied as above with one exception. The roots of each grass plant were encased in plastic wrap to protect from the herbicide application. Plants were next placed in the solution and allowed to grow for one week. Grass plants were then removed leaving any herbicide root exudates in hydroponic solution. Cucumber plants were then inserted into the hydroponic solution and allowed to grow for 3 weeks. Sensitive plants were then visually rated, weighed, and measured. Only tall fescue data was utilized in this study due to nutrient toxicity effects. Soil study data indicated that dicamba resulted in significantly more damage to sensitive species than did ACPC. Dicamba and ACPC treated pots exhibited greatest damage to sensitive species at 3 WAT. Dicamba treatments ranged from 80 to 93% control representing bermudagrass and bahiagrass respectively. ACPC treatments provided 8% control with all species with the exception of bermudagrass. Bermudagrass pots exhibited 50% control indicating that bermudagrass exuded the most ACPC. The result of the hydroponic study indicated 71% control to sensitive species treated with dicamba at 3 WAT and 12% control to sensitive species from ACPC treatments. Based on these data, ACPC does exude through plant roots after foliar treatment into the surrounding environment in all species evaluated but the effect is minor and less than dicamba.