Mechanism of control of eyespot disease in winter wheat by the fungicide prochloraz

Abstract Winter wheat plants grown in troughs and infected with the eyespot pathogen ( Pseudocercosporella herpotrichoides ) were sprayed with prochloraz at growth stage (GS) 31 and 39 using a hydraulic nozzle sprayer and with a drop-leg spray system at GS 39. Some plants received artificial rain (4 mm) 1 or 4 days after spraying and were compared with those not receiving rain, with respect to foliar and stem-base fungicide deposits, as well as control of eyespot disease. Single pot-grown plants were treated topically with prochloraz inside the leaf axils and examined for redistribution of the fungicide by rain as well as the effect on eyespot disease. Rain redistributed the fungicide deposited by the hydraulic nozzle spray system from the initial site of deposition to the base of the crop at GS 31 and 39 and significantly suppressed eyespot disease development. No similar effects were found on the crop sprayed by the drop-leg system. The effect of rain on plants treated by topical placement of the fungicide in leaf axils was to redistribute prochloraz downwards between the outer leaf sheath and the stem, thus suppressing eyespot disease.