EFFECT OF DROUGHT STRESS, ABSCISIC-ACID, AND ABSCISIC-ACID ANALOGS ONTHE EFFICACY OF DICLOFOP-METHYL AND TRALKOXYDIM

The effects of drought stress, abscisic acid (ABA), and four ABA analo gues on diclofop-methyl and tralkoxydim efficacy were investigated in oat (Avena sativa). Drought stress conditions (6% soil moisture conten t) reduced the efficacy of diclofop-methyl at 350 g ha(-1), but not at 700 g ha(-1). Similarly, tralkoxydim efficacy was reduced by drought stress at 62.5 and 125 g ha(-1), but not at 250 g ha(-1). ABA (100 mu M), applied as a root drench 2 days before the herbicide, protected oa t plants against all rates of diclofop-methyl and against low rates of tralkoxydim. Two ABA analogues protected oat plants from diclofop-met hyl injury, whereas two others had no effect. Foliage applications of ABA were much less effective than root applications in protecting agai nst herbicide injury. Protection by ABA and the two active analogues w as dependent on the relative time of application with respect to the h erbicides. Optimal protection by ABA and analogue I was obtained when they were applied between 2 days before and 1 day after diclofop-methy l application. Analogue IV protected plants when applied between 3 day s before and 1 day after diclofop-methyl application. Partial protecti on against tralkoxydim activity by ABA was observed when it was applie d between 1 day before and 1 day after herbicide application. Analogue I did not afford any protection against tralkoxydim, and analogue IV afforded partial protection when applied the same day or 1 day after t ralkoxydim. The results indicate that protection against these posteme rgence herbicides, similar to that conferred by water stress, can be i nduced by ABA and structural analogues that apparently mimic the actio n of ABA.