Response of Susceptible and Putative Resistant Goosegrass (Eleusine indica) Populations to Protoporphyrinogen Oxidase Inhibitors

Abstract

Goosegrass is considered one of the five most troublesome weeds in the world (Holm, 1991). Goosegrass is commonly found in high traffic and stress areas where the desired turf is thin and vulnerable for weed infestations. The use of preemergence herbicides has become important for goosegrass control because of limited options for postemergence control. Studies were conducted to investigate oxadiazon suspected-resistant goosegrass populations from Richmond, VA. The SR populations showed minimal response to increasing oxadiazon rates while susceptible populations showed greater tissue damage and plant necrosis. Research suggests that there is a resistance mechanism within the SR populations. Greenhouse studies were conducted to evaluate the response of oxadiazon-resistant goosegrass to postemergence applications of protoporphyrinogen oxidase inhibitors. Studies were conducted to determine response of five goosegrass ecotypes (‘Craft Farms’, ‘CCV’, ‘RB’ ‘Alabama Crop Wild Type’, and ‘Texas’) to oxadiazon, flumioxazin, and sulfentrazone. A dose response curve was developed to predict at which rate a goosegrass population will be inhibited. The rate at which a given herbicide inhibits growth 50 and 90%, also referred to as I50 and I90 values are commonly presented in dose response research. Estimated i values from susceptible (S) seed were several orders of magnitude higher than i values from oxadiazon resistant (OR) plants. The OR populations in Auburn University trials required an estimated 13.65 and 3522 kg ai ha-1, respectively, of the population at 42 DAT while the Craft Farms (S) plants required only 0.23 and 2.52 kg ai ha-1, respectively. These data indicate that oxadiazon rates required to achieve commercially acceptable control (90%) were significantly higher for the SR than the S successions.