Redistribution of foliar surface deposits of prochloraz by simulated rainfall and the control of eyespot disease of winter wheat

Abstract Outdoor-grown wheat plants sown in troughs and infected through indirect inoculation with the eyespot pathogen ( Pseudocercosporella herpotrichoides ) were sprayed with prochloraz in a spray chamber at Zadok GS 37. Prochloraz was applied in either low (151/ha) or normal (2001/ha) spray volumes to plants standing vertically or laid on their sides and masked to preclude spray deposition on the stem bases. After spraying, plants were kept in a glasshouse and a proportion were exposed to one or more light (0·4 mm total) or heavy (4·0 mm total) artificial rainfall regimens. Immediately after spraying with recommended amounts of fungicide, only traces were found on stem bases of plants sprayed vertically and, in the absence of rain, eyespot incidence was unaffected. Heavy rain applied one day after fungicide application redistributed from the foliage to the plant base c . 5·5 μg prochloraz/g stem tissue and decreased eyespot severity. Light rain redistributed less fungicide and had a smaller effect on eyespot. Spray volume had no effect on redistribution or disease control. The half-life of prochloraz on unweathered foliage was c . 6 days, but at the stem base, deposits changed little over two weeks.