Abstract: Relationship between nutritional status of open field grown Thompson Seedless grapevines and powdery mildew incidence was studied for two years at two growth stages. Amongst different nutrients, potassium showed highest degree of significant and negative correlation with the powdery mildew disease rating (r= -0.817 and -0.875) at two growth stages. Regression analysis also revealed the importance of potassium nutrition in powdery mildew incidence. During the first year of the study, N, P, K, Ca, Mg and Na when regressed together accounted for 82.7 % (R² = 0.826) variation in disease incidence and potassium alone accounted for 66.8 % variation in disease incidence (R² = 0.667). During the second year N, P, K, Ca, Mg and Na when regressed together accounted for 85.7 % (R² = 0.857) variation in disease incidence and potassium alone accounted for 76.6 % variation in disease incidence (R² = 0.765).