Combining host plant resistance and managed fungicide applications for control of late blight in potatoes

Fluazinam, a new protectant fungicide with excellent residual activity and active in relatively small doses, was applied on potato foliage in combination with cultivar resistance. Three rates [33, 66 and 100% of the manufacturer's recommended application rate (MRAR)] of fluazinam were applied on 5, 7, 10 and 14-day application intervals in 2001; two rates [50% and 100% MRAR] on 5, 10 and 15-day application intervals in 2002 and examined for foliar late blight control. The results of this study showed that reduced amounts of fluazinam were either partially or fully effective at all application rates tested on all cultivars compared to the non-treated controls at P = 0.05. On susceptible cultivars, applications of fluazinam at 10-day spray intervals or above were partially effective for controlling late blight at the doses tested. All cultivars treated at 100% and 50% MRAR of fluazinam were effectively protected against late blight on a 5-day spray interval and partially protected at all other rates and application intervals. Application of fluazinam at reduced rates and frequencies could successfully be used into a control program using host resistance. The impact of plant age and leaf position on susceptibility to potato late blight infection was also assessed. Susceptibility to potato late blight infection decreased with plant age and leaf position; from young plants to the old ones and from leaf 5 to leaf 15 in the cultivars tested.