Biological Assay Techniques for Detecting Root Leakage of Auxin Mimic Herbicides.

ABSTRACT

Biological assay (bioassay) techniques are a useful tool in determining the presence of herbicides in soil or other potting media. These techniques utilize a plant species susceptible to a known herbicide for this task. 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 exists when applied at labeled rates. It was compared with dicamba, a herbicide known to exude from plant roots and a non-treated check. Bioassay studies were conducted utilizing four graminaceous species including bahiagrass (Paspalum notatum), bermudagrass (Cynodon dactylon), cogongrass (Imperata cylindrica), and tall fescue (Schedonorous arundinaceus) as target species with cucumber representing the sensitive species. The study utilized Marvyn Sandy Loam soil as potting media. Data indicated that dicamba treatments resulted in significantly more damage to bioassay species than did ACPC treatments. Dicamba treated pots exhibited 59, 67, and 85% damage to bioassay species at 1, 2, and 3 WAT respectively. ACPC treatments resulted in 11, 12, and 18% damage to bioassay species across the same time intervals relative to the non-treated. Based on these data, ACPC does exude through plant roots after foliar treatment into the surrounding environment in all species but is minor and less than dicamba.