Studies on shiny spot symptom development on grapevine leaves and its effect on fruitfulness, disease incidence and vine yield.

Shiny round or elliptical spots were observed on the leaves in many table and wine grape varieties. Initially a reflecting surface was formed which appears like shallow colourless oil spot. Nutrient composition of vines having no symptomatic leaves (healthy) and vines exhibiting symptoms (affected) vine tissues was compared to find out association of mineral nutrients with the symptoms. Petioles collected from affected vines contained significantly lower K content (0.59% K) compared to petioles collected from healthy vines (1.17% K) exhibiting no symptoms. The differences with respect to other nutrients in petioles viz., N, P, Cl, Cu, Zn, Fe, and Mn were not significant. The K content was also significantly lower in the leaf blades of the affected vines compared to healthy vines. The symptom development could be controlled by foliar as well as soil application of K fertilizers. Fruitful canes/vine, yield/vine and average bunch weight were significantly reduced in affected vines compared to healthy vines. The vines having symptomatic leaves were highly sensitive to powdery mildew infection.