SUSCEPTIBILITY OF JAPANESE PLUM CULTIVARS TO TRANZSCHELIA PRUNI-SPINOSAE UNDER ORGANIC AND CONVENTIONAL MANAGEMENT IN SOUTHERN SPAIN

The susceptibility of 14 commercial plum cultivars to rust disease, caused by Tranzschelia pruni-spinosae (Pers) Dietel was tested in two orchards, organic and conventionally managed, from 2007 to 2009. The disease was estimated by measuring both the incidence and severity on the plants. Overall, the rust disease level was higher in the organic orchard despite attempts at treatment using wettable sulphur and Equisetum spp. excerpt. By contrast, in the conventional orchard the disease progression was properly blocked by treatment with cyproconazole and mancozeb. In the organically managed plot, the sporulating leaf lesions appeared in early July in ‘Showtime’, ‘Friar’, ‘Sapphire’, ‘Larry-Ann’ and ‘Santa Rosa’; these five cultivars showed the highest rust severity index. Other cultivars like ‘Songold’, ‘Fortune’, ‘Primetime’, ‘Angeleno’, and ‘Blackamber’ displayed a greater tolerance to the rust disease, and ‘Red Beaut’ and ‘Souvenir’ were the most resistant cultivars. In the conventionally managed orchard when the effect of the latest treatment ceased the rust spreaded and a similar cultivar behavior was observed, although the symptoms appeared later, in late September. The disease level increased in both types of management until late November before autumn defoliation. The rust attack in the organic orchard caused a premature defoliation, especially in the most susceptible cultivars.