Epidemic outbreaks of downy mildew caused by Plasmopara halstedii on sunflower in Thrace, part of the Marmara region of Turkey.
During the spring of 2007 and 2008, a serious outbreak of downy mildew caused by Plasmopara halstedii at the V4 (four true leaves) stage of development was observed on sunflower plants grown in commercial fields in Thrace, part of Marmara, the main producing area in Turkey. It is thought that low temperature and extensive spring rains encouraged the disease, resulting in approximately 85% yield loss and lower quality of sunflower production in some areas. Plants carrying systemic downy mildew infection were stunted and leaves showed characteristic green and chlorotic mottling along the main veins and over the lamella. Under moist conditions, a white downy growth composed of sporangiospores and sporangia of the fungus appeared on the leaf surface. P. halstedii is listed as an A1 quarantine pest by IAPSC, but not by any other regional plant protection organization. However, Australia treats it as a major quarantine pest. EPPO is currently examining its quarantine status.