Monday, November 5, 2007 - 9:05 AM
72-6
Comparison of Four Bioassay Methods for Evaluation of Potential Mitotic-Inhibiting Herbicide Resistant Poa annua.
Dinitroaniline herbicide resistant annual bluegrass (<i>Poa annua<i/> L.) has been reported in North Carolina due to the repeated use of prodiamine in golf course fairways. However, in Tennessee there have been no reported cases of annual bluegrass resistance to any dinitroaniline herbicides. Reduced preemergence control of annual bluegrass with prodiamine was reported at Eagle Bluff Golf Course in Chattanooga, Tenn. Seeds were harvested from Eagle Bluff and evaluated for dinitroaniline and dithiopyr resistance. The four plant response tests utilized to detect resistance were the gel-media, filter paper, petri-dish, hydroponic, and soil container bioassays. Hydroponics utilized tillers from fully developed plants, while all other screens utilized mature seed. All the bioassays revealed that the Chattanooga population was more resistant to dinitroanilines than the sensitive control. More root growth was exhibited by the Chattanooga population than the sensitive at 1.0 mM of the dinitroanilines in all the laboratory screens. No resistance was detected to dithiopyr. The gel-media bioassay was the most accurate screen due to its minimization of confounding variables such as microbial degradation, uneven herbicide distribution, and fungal contamination. Diagnosis was obtained the fastest utilizing the hydroponic bioassay. Hydroponics acts as an accurate screen if a liquid formulation such as an emulsifiable concentrate of a herbicide is used. Formulation such as wettable powders are difficult to agitate in the hydroponic containers. Both hydroponics and gel-media bioassays improve upon previous screening methodologies.
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