Abscisic acid as a protectant of Avena fatua L. against diclofop‐methyl activity

Summary The imposition of water stress before or al the time of spraying diclofop‐methyl reduced efficacy against wild oat (Avena fatua L.). Similar reductions in herbicide performance were obtained by application of 20 μg of the methyl ester of abscisic acid (ABA) to plants with three to four leaves before spraying with I kg ha−1 diclofop‐methyl. Application of 40–100 μg ABA per plant effectively protected plants against damage from diclofop‐methyl applied at 1 5–2 0 kg ha −1. The application of 20 μg ABA induced rapid stomatal closure and a reduction in leaf extension rate, which were sustained for 7–8 days after treatment. These changes were associated with an overall reduction in shoot growth. ABA‐treated plants that were additionally sprayed with diclofop‐methyl sustained ABA symptoms, but no additional weight loss or leaf chlorosis. The mechanism of the protective action of ABA on diclofop‐methyl has not been determined.