Study on the STOP effect of fungicide combinations to control late blight in potato.

The effectiveness of different fungicide combinations to control late blight and the STOP effect of these fungicide combinations for the control of foliar and tuber blight under high infection pressure was investigated. Last summer late blight development was arrested in July due to high temperatures and lasting drought. In August the weather was cloudy, rather cold and a lot of rain. These weather conditions were very favourable for late blight. Due to the heat waves of June and July the foliage started to die allready in August and P. infestans developped very fast in the second part of August. Because of that no incidence of foliage blight was scored. No significant differences in yield were observed for the different treatments applied. The combination cyazofamid + heptamethyltrisiloxaan (Ranman) + propamocarb + chlorothalonil (Tattoo C) had the highest yield. The percent diseased tubers fluctuated between 14,9 and 45,1 % for the different treatments tested. The amount of blighted tubers was lowest for fluazinam (Shirlan) + cymoxanil +chlorothalonil (Mixanil) and fluazinam (Shirlan) + benthiavalicarb + mancozeb (Valicarb).