Control of sunflower downy mildew with metalaxyl.
Seed dressing with metalaxyl at 1, 2 or 4 g a.i./kg prevented Plasmopara helianthi [P. halstedii] sporulation on seedlings inoculated by dipping the roots into a zoosporangial suspension. Washing seedlings with water before inoculation did not affect the results, suggesting a systemic activity within the seedlings. One or 2 drenches of soil in pots, at 125, 250 or 500 mg a.i./l, reduced symptom severity in infected seedlings and allowed normal growth to resume. Symptom remission was also achieved with field sprays. Highest remission occurred with 3 sprays at 520 mg a.i./l and 2 or 3 sprays at 1040 mg/l.