Leveillula taurica (powdery mildew of cotton)

The host organ most affected by Leveillula is the leaf blade. Petioles, stalks and flowers are rarely affected and fruits are occasionally infected. L. taurica penetrates the interior leaf tissues and symptoms are usually apparent on the ventral side as powdery, whitish spots that gradually expand. On the dorsal side, yellow spots of varying intensity develop opposite the spotted ventral side. On the dorsal side, powdery spots may also develop. Spots may later become necrotic.The spots are bright yellow on leaves of tomato, pepper and lucerne, while on cucurbits, aubergines, onion, cotton, sesame and olive the spots are pale yellow.Leaf shedding occurs on pepper, guar, cotton, some varieties of aubergine, poinsettia and olive. Once leaves are shed the fruits may be exposed to direct sun irradiation and damaged.

Crops suffer significant losses due to Leveillula powdery mildew when attack starts at younger growth stages and develops fully at stages before ripening of fruits. The epidemics develop well in dry and warm regions. The potential for losses is greater in crops that are irrigated.Minor losses are reported for crops such as castor bean, jute, chickpea, broad bean, mung bean, potato, onion and garlic whereas lucerne, coriander, kenaf, sesame and safflower suffer occasional yield reductions due to L. taurica (Palti, 1988). Crops that may suffer major reductions in yield are pepper, aubergine, tomato, artichoke, fenugreek, guar, cucurbits, mulberry, nasturtium, hollyhock, calla lily and Euphorbia spp. (Palti, 1988).On pepper (Capsicum), data from open field experiments with fungicides showed that unsprayed controls yielded 50% less than plots protected by fungicides (Barak et al., 1980).On tomatoes, crop losses of 40% have been reported (Jones and Thompson, 1982) while on legumes, 54% crop loss has resulted from infection (Sharma and Sohi, 1981).