| The powdery mildew on cucurbits was researched in Jilin Province China. The pathogen mainly infected leaves and petiole. Powdery mildew was first seen as whitish colonies on the both side of the leaves. The colonies enlarge and coalesce to cover much of the leaf surface that look as if flour or lime had been dusted over the leaves. The conidia were 23-46μm×13-24μm, and produced on conidiophores. The conidia were in chain or single, ellipse, colorless. Cleistothecia was not found. The results of pathogenicity test showed that the disease index of muskmelon was the highest, pumpkin's was the lowest. The pathogeny on Cucumis sativus, Cucumis sativus, Cucurbita pepo(Squash) and Cucurbita pepo(Marrow) besides watermelon could invaded each other after the it inoculated each other.The biological characters of the pathogens were systematically studied. The result showed: the spores began to germinate after 4 hours during the culturing, the germination rate was 90.5% after 24 hours. The spores could germinate between 10-35℃, and they couldn't germinate under 10℃or above 35℃; the optimal temperature of conidia germination was 23-28℃. The higher of the humidity was, the higher of germination rate was. The change of light and dark was good for conidia germination. The conidia could germinate in all carbon resources, the germination rate was the highest in glucose. The conidia germination rate was much low or the conidia couldn't germinate in nitrate resources tested. The germination rate of high spore density was higher than that of low density. The temperature causing conidia death was about 55℃.The studies on the incubation period and symptomatic appearance and expanding of the lesion showed: the incubation period of the powdery mildew on melon, cucumber, Squash and Marrow was 4-5 days. The temperature had much effect on incubation period. The incubation period under 10℃was the longest. Symptomatic appearance could last 5 days. During the different growth period of melon plant, the incubation period was same. The size of lesion on different cucurbits was different, and was the biggest on melon. The speed of spores production was affected by humidity, and was the fastest under RH 100%. There was little different on the number of spore of single lesion among various cucurbits. The number of spores on a single lesion was the most under the change of light and dark. And there was no relationships between the scale of lesion and the age of lesion. The lesion could product many spores under the humidity of 80-90%. The earlier planting time was, the more was the number of spore. A small quantity of nitrogenous fertilizer could suppress lesion to produce spore, the effect of excessive nitrogenous was opposite; phosphate fertilizer could accelerate lesion to produce spore, the potassium fertilizer was opposite.The studies on the disease cycle showed that rotation could decrease the disease. The results of resistance research showed that all the tested cucurbits were susceptible to the disease. The susceptibility of marrow was the lightest, and the melon was the heaviest. With the growth of plant, the resistance to infection was weaker and weaker.The spores disseminated mostly in the daytime. The distribution model of powder mildew was assemble.The best chemical for the control of powdery mildew was Diniconazole, Difenoconazole, Myclobutani and Azoxystrobin were also effective. The worst was Carbendazim and Daconil which were less used nowadays.
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