In order to save the Egyption ecosystem from pollution with pesticides, under laboratory conditions . application of potassin (P) , mixed with (N + P + K) , potassium sulphate and potassin (N)  at 800 ppm in vitro decreased conidia germination and length of germ tube of Erysiphe cichoracearum . However the least effective treatment was Urea (N) .Under field condition , all tested macroelements as foliar spray reduced powdery mildew disease severity . Application of (N + P + K), potassin- F , potassium sulphate and calcium supper phosphate resulted the best effects . Disease severity was reduced to 18.14 , 18.95 , 19.78 and 20.96% respectively compared with control 63.65% . Observed results clear The Topase and sulpher micronized fungicide gave the best disease control .Two field experiments were carried out on squash cv . Eskandrani in the two summer season 2003 and 2004 to study the effect of foliar application with Urea 1% , calcium super phosphate 1% , potassium sulphate 1% + potassium sulphate 1% , potassin-N 2.5 ml/l , potassin-F 2.5 cm/l , Topas 0.25 ml/l and sulpher 2.5 gm/l on growth , sex expression , yield , chemical composition and disease severity of powdery mildew of squash plants . The results revealed that , vegetative growth (number of leaves , plant height , fresh and dry weight ) were significantly increased by foliar application with all treatments compared with control .Spraying squash plants with Topase gave the highest values of number of fruits per plant , morever , foliar spray with salpher micronized gave the highest values of fresh and dry weight plants . Average fruit weight , early yield and total were obtained by foliar application squash plants with Urea 1% + calcium super phosphate 1% + potassium sulphate 1% and potassin-N 2.5ml/l . The chemical composition of the leaves revealed that different treatments used significantly increased N , P and K compared with control . In general , it can be stated that foliar application with Urea 1% + calcium super phosphate 1% + potassium sulphate 1% and potassin-N 2.5 ml/l were recommended to raise squash production under the environment condition of this investigation .