FLURIDONE CONCENTRATION AND EXPOSURE TIME REQUIREMENTS FOR CONTROL OFEURASIAN WATERMILFOIL AND HYDRILLA

Fluridone concentration and exposure time requirements were evaluated for Eurasian watermilfoil (Myriophyllum spicatum L.) and hydrilla (Hyd rilla verticillata (L.f.) Royle) under controlled-environment conditio ns. Results indicated that fluridone effectively inhibited growth and reduced biomass at rates of 12, 24 and 48 mu g/l. Shoot and root bioma ss and total chlorophyll were reduced from 70 to 98% following 30-, 60 - and 90-days exposures to fluridone. However, removal of fluridone at 30 and 60 days resulted in extensive regrowth following a 30-day reco very period. One exception was milfoil exposed to 48 mu g/l for 60 day s which was reduced by approximately 98% with no evidence of regrowth. The 48-mu g/l treatment often resulted in greater biomass reduction i n both species than the other rates; however, no significant differenc es were noted between the treatment rates of 12 and 24 mu g/l. Results indicate that maintaining fluridone concentrations for >60 days at ra tes as low as 12 mu g/l is critical for successful fluridone treatment s.