EPIDEMIOLOGY AND INCIDENCE OF TOMATO YELLOW LEAF CURL VIRUS (TYLCV) IN GREENHOUSE PROTECTED BY SCREENS IN ITALY

The tomato yellow leaf curl virus is a limiting factor for tomato yield in Sicily. The disease shows a wide seasonal variation. TYLCV infections have been monitored in 1990 and 1991. The virus incidence was more severe in crops transplanted in August, whereas a low disease level was found in crops transplanted in October. The whitefly penetration into plastichouses and the disease incidence were related with the mesh density of the various screens tested. A delay in infections was observed in the plastichouses protected by screens. A good correlation between whitefly populations and TYLCV disease was found only during hot months. Yield losses ranged from 24.6 to 80.7 % in relation to the infection period. The symptomatology depends on the temperature and the time of infection. The spatial pattern of the virus-diseased plants was not constant during the epidemics studied. In spite of the fact that screens were used to limit spread of the disease in the crops transplanted in August, numerous insecticide treatments were required.