The NegFry model used for timing the chemical control of potato late blight was validated in field trials at Bonin in the years 2001-2002 (4 trials). In these trials the number of fungicide treatments recommended by NegFry was about 34.5% lower (on average) than the number of treatments in a routine spraying scheme. This reduction was mostly the results of a delay in the time of the initial fungicide application and longer spraying intervals recommended by Negfry.