Sunflower (Helianthus annuus) is the most important oil crop in Serbia, that produces high quality oil for human consumption and technical purposes as well. Sunflower is attacked by more than 40 different diseases of which only a certain number causes serious problems in the production process. Among these, the most important are phytopathogenic fungi. One of the most damaging diseases is downy mildew which is caused by Plasmopara halstedii fungus (Farl.) Berl.et Toni. (syn. Plasmopara helianthi Novit.). In conditions that favour its development it can reduce the yield of the sunflower by 50%. Many physiological races of this fungi hinder the control of the disease and that's why agrotechnical, chemical and quarantine measures should be applied. As the dominant race in our country is race 730, the testing of the selected material is aimed at creating hybrids of high resistance to this particular race of downy mildew. Other races are also taken into consideration and evaluated. As downy mildew occurred during the vegetation period in 2008, this research was designed to investigate the efficiency of fungicides, applied in case of secondary infection. We have measured oil and protein contents, germination and pathogen presence in seed of treated plants. Crops infested with Plasmopara helianthi and treated with Ridomil, developed healthy seed with unchanged oil and protein contents in comparison with non-treated healthy crop. According to given results, we can confirm that, when secondary infection of downy mildew appears, treatment with fungicides are reliable. Following NS hybrids in Serbian commercial sunflower production that contain Pl-6 gene, conferring resistance to most important races of downy mildew are recommended: Sremac, Duško, Plamen, Kazanova,Velja and Rimi PR.