向日葵霜霉病Plasmopara halstedii(Farl.)Berl.& de Toni是一个经济重要性很大的种传兼土传的毁灭性病害。在适宜的气候条件下,它能致使田间植株死亡70％～80％,并严重降低种子萌发。在北美地区向日葵是Plasmopara halstedii的主要寄主,它已传播到南北美洲的许多国家、欧洲和苏联(英联邦真菌学研究所植物病害分布图№266),但是在澳大利亚和印度还没有发生的报道。在近15年中,印度的许多地区确定向日葵为大量生产的作 Sunflower Downy Mildew Plasmopara halstedii (Farl.) Berl. & De Toni is an economically important germ-killing devastating disease. Under suitable climatic conditions, it can kill 70% to 80% of the plants in the field and severely reduce seed germination. Sunflower in North America is the main host of Plasmopara halstedii, which has spread to many countries in North and South America, Europe and the Soviet Union (Commonwealth Mycology Institute Plant Disease Map №266), but has not been reported in Australia and India. In almost 15 years, many parts of India have identified sunflower as a mass-produced crop