Powdery mildew of squash caused by Sphaerotheca fuliginea is more prevalent in Egypt, in Summer and Nili plantations than in the Winter . The effect of spraying different salts on disease incidence was studied. Results revealed that KCl, KH2PO4 and K2CO3 were generally effective in powdery mildew control. It was also concluded that potassium salts at concentrations of 750 ug/ml decreased infection, as compared with the fungicide Prochloraz either applied after or before symptom development. Biochemical changes associated with salt application possibly induced systemic resistance. The presence of common protein bands were recognized. Electrophoretic analysis of extracted proteins on polyacrylamide gel showed greater number of protein bands with fungicide treatment as compared withK2CO3, KCL, KH2PO4 and the control.