EFFECT OF APPLICATION TIMING ON PYRITHIOBAC PERSISTENCE

Experiments were conducted in 1993 and 1994 to determine persistence o f pyrithiobac as determined by bioavailability following different app lication times in a silty clay. Pyrithiobac was applied at PPI, PRE, p inhead square (PHS), and first bloom (FB) application timings. Greenho use studies were also conducted in 1993 and 1994 to determine pyrithio bac persistence under controlled conditions on a sandy loam soil. Slop e comparison indicated no difference in degradation patterns in the fi eld for any application timing of pyrithiobac within years; thus, appl ication timings were combined for 1993 and 1994. Slope comparison also indicated no difference in slope between 1993 and 1994; thus, years w ere combined to determine pyrithiobac persistence. The initial concent ration was 30 eta g g(-1). The half-life of pyrithiobac was 62 d in th e field. Analysis of covariance indicated no difference in slope for t he 1993 and 1994 greenhouse studies, and years were combined to determ ine the half-life. The initial concentration was 43 eta g g(-1). The h alf-life was 43 d in the greenhouse study.