Fungicides considered as most effective method of controlling powdery mildew diseases on cucurbits, but there remains more than one challenge facing this method, and one of major challenges is resistance in pathogen populations, as well as their harmful impact on the ecosystem.Six commercial algae products besides green algae extract were applied to estimate their effectiveness against powdery mildew disease in squash plants under field condition during two successive seasons 2020-2021. In addition to studying the role of algal formulations used in increasing the resistance of squash plants against powdery mildew, this is through its effect on some biochemical changes within the plant, which in turn increases the plant's ability to resist disease. The results of this study showed that the correlation between the incidence of the disease and the content of the leaves of total soluble phenols is negative, and the value of this correlation reached 28%. The same result was obtained with the leaves content of total proteins, the correlation value reached 51%. PPO and acid invertase showed the same trend. In the end, we can say that the use of algal extracts and their formulations may provide an ideal choice to control powdery mildew disease on squash plants, whether by its direct effects on the disease or even through the indirect effect by increasing the level of phenolic substances and proteins as well as stimulating some enzymatic systems through which the plant can defend itself against disease.