Reduction of torpedograss (Panicum repens) canopy and rhizomes by quinclorac split applications.
Two field experiments were conducted in 1999 and 2000 to evaluate the reduction of torpedograss canopy by multiple split applications of quinclorac applied postemergence (POST) to bermudagrass (Cynodon transvaalensis × C. dactylon) golf course roughs in Broward, Florida, USA. In one experiment, quinclorac treatments were reapplied for a second year to the same plots, followed by biomass harvest, to evaluate the reduction of torpedograss rhizomes. Quinclorac sprayed at 1.68 kg/ha (annual rate) visually reduced torpedograss canopy to a varying extent, depending on the number of split applications. The most effective treatment, 0.42 kg/ha quinclorac applied four times each year for 2 years, reduced torpedograss canopy to 10% compared with 86% torpedograss canopy in the untreated plots, and reduced torpedograss dry weight to 1570 kg/ha compared with 8010 kg/ha in the untreated plots. After reapplication for 2 years with the commercially labelled treatment, quinclorac at 0.84 kg/ha applied twice per year, torpedograss canopy was reduced to 45% and dry weight to 4640 kg/ha. Visual evaluation of canopy was too optimistic in representing the herbicidal control of torpedograss by quinclorac because torpedograss regrew from rhizomes, and canopy was a relatively small part of the plant. In plots not chemically treated, pachymorph rhizomes were 63%, leptomorph rhizomes were 24%, and leaves were only 13% of the total dry weight of torpedograss.