ÖZETErzurum Pasinler Ovasıııda Zirai Araştırma Enstitüsü ayçiçek denemelerinde1981 yılında dikkati çeken hastalık Plasmopara helianthı' Novot,un oluşturduğuayçiçek mildiyösü olarak belirlenmiştir. O yıl sadece Trakya dan gelirıi/en ayçiçektohumlarından oluşan bazı bitki/erde ortaya çıkan hastalığın, 1982 yılında çevredekiçiftçilerin ayçiçek ekim alanlarına da yayıldığı görülmüştür. Yörede ayçiçeklerindesadece primer sistemik enfeksiyonlara neden olan fungusun sekonder enfeksiyon/arıoluşmamıŞtır.DOWNY MILDEW OF SUNFLOWERS (Plasmapara helianthi Novot.)IN THE PROVINCE OF ERZURUM-TURKEYSUMMARYThe disease recorded on sunflowers in 1981 at the Agricultural ResearchInstitute Station in Pasinler Plain of Erzurum, was identified as downy mildewcaused by Plasmopara helianıhi Novol. In 1981 downy mildew of sunflowersappeared only on some plnnts developed from the seeds brought from Thrace.But in 1982 it was found to be spreaded to the sunflower fields of the farmersaround the research station. So it was believed that the disease was introdueedto this region by the infected seeds brought from Thrace and the residues of theseplants were served as an inoculum source for the next year's crop. In 1982 the di·sease was mainly found on the plants sown before the spring r~ins which providefree soil water for the spread of the pathogen in soil from the plant reSİdues. Nosecondary Jocal infections were observed in the distrlct, although sporüİation \-vasseen after the rainy periods on the leaves of systemicaI1y infected plants.' Thefailure in the oCcurance of secondery infections was attributed ,to the short dura·tin of windy moisı periods during the time of secondery spread.