DISSIPATION OF GIBBERELLIN SYNTHESIS INHIBITORS IN SMALL-SCALE AQUATIC SYSTEMS

Water, plant and soil samples from 67-L barrels planted with Eurasian watermilfoil (Myriophyllum spicatum L.) and exposed to the gibberellin synthesis inhibitor flurprimidol ([alpha-(1-methylethyl)-alpha-(4-tri fluoromethoxy) phenyl]-5 pyrimidinemethanol) were analyzed for flurpri midol using gas chromatography. Half lives of flurprimidol in water an d plant tissues were 8.4 and 9.1 days, respectively, at an initial tre atment concentration of 75 mug a.i. L-1 and 9.8 and 8.8 days, respecti vely, at an initial treatment concentration of 200 mug a.i. L-1. Half life of the compound in sediment at an initial treatment concentration of 1000 mug a.i. L-1 was 178 days. Approximately 14.5% of the flurpri midol initially applied was recovered after 28 days of exposure. An in ternal threshhold level of 20-30 ng flurprimidol per gram dry weight m ilfoil tissue appeared to be necessary for maintaining adequate stem h eight reduction. Dissipation characteristics of two other gibberellin synthesis inhibitors, paclobutrazol -chlorophenyl)-4,4-dimethyl-2-(1,2 ,4-triazol-1-yl) penten-3-ol]) and uniconazole hlorophcnyl)-4,4-dimeth yl-2-(1,2,4-triazol-1-yl)-1 penten-3-ol), differed from those of flurp rimidol. Half lives of paclobutrazol and uniconazole in water were 24. 4 and 5.2 days, respectively. The half life of uniconazole in soil was 102 days whereas paclobutrazol did not dissipate over the 168 day sam pling period.