FUNGICIDES AND PLANT PRODUCTS EVALUATION FOR CONTROL OF POWDERY SCAB OF POTATO

Powdery scab of potato, caused by Spongospora subterranea, is a direct quality-limiting disease which can also reduce crop productivity. Recently, in Merida state, Venezuela, an increase of disease incidence and severity has been observed, reaching up to 100% in crop losses. As there is not a unique effective method of control, integrated management practices must be developed. In order to evaluate the effectiveness of commercial fungicides and plant products on the incidence and severity control of the disease, a field trial was performed under a randomized complete block design. Five commercial fungicides were evaluated (mancozeb, azoxystrobin, propamocarb, difenoconazole and PCNB) as well as two plant species (Lippia origanoides Kunth and Calotropis procera (Ait.) Ait. f) in two forms (ethanolic extracts and powder). Treatments were applied at 4 and 8 weeks after sowing. At harvest, potato tubers were classified according to their size and weight in A, B and C classes. Disease severity reduction (P=0,0365) was found on B class tubers. Mancozeb, L. origanoides (ethanolic extracts), azoxystrobin and C. procera (powder) reduced disease severity by 2.47, 3.20, 3.82 and 4.08%, respectively. There were no significant differences in disease incidence (P>0,05) among treatments. The decrease of the disease severity led to an increase in the yield of B class tubers. The results indicate a potential for the evaluated treatments in control of the potato powdery scab.