Containment of existing potato late blight (Phytophthora infestans) foliar epidemics with fungicides

Critical timing of application of foliar fungicides to limit further infection of potato foliage by Phytophthora infestans and the critical threshold of foliar infection level at which individual or combinations of specific fungicides limited further spread of infection with P. infestans were determined. In most seasons, key application timings at which the foliar late blight epidemic was contained to < 50% of that in untreated control plots, were programs initiated 72 h before and 72 h after inoculation with P. infestans, and when foliar area with late blight lesions was estimated to be 1% or less. Delaying initiation of application of any fungicide until 5% and 10% estimated average foliar area with late blight lesions resulted in late blight development similar to the untreated control. Most fungicides and fungicide mixtures examined resulted in 30 50% reduction of late blight development in comparison to the untreated control as long as they were applied not later than 1% estimated average foliar area with late blight lesions. (C) 2002 Published by Elsevier Science Ltd.