Five soybean cultivars; Crawford, Clark, Giza 21, Giza 35 and Giza 82 were
evaluated for the control of downy mildew infection under greenhouse and field
conditions using three different fungicides. In vitro studies show that Sandofan M-8 and Ridomil plus were more effective against the spore germination and germtube length of Peronospora manshurica the causal pathogen. Complete inhibition of the spore germination and germtube was obtained at 100 ppm of Sandofan M-B, and 200 ppm for Ridomil plus and Dithan M 45. The fungicide application under greenhouse conditions, 2 days before or 2 days after inoculation by the pathogen spore suspension at the rate of 1x10⁵ sporeslml was also studied. It was observed that, the cvs. Giza 35 and Giza B2 showed lower infection than the other tested cvs., however Crawford gave the highest infection. The fungicide Sandofan M-8 was the most effective on downy mildew followed by Ridomil plus and Dithan M 45 either two days before or after inoculation. Field studies at both Sakha and Itay EI-Baroud in the growing season 2000 gave as similar results as the greenhouse. The obtained results indicated that three sprays of Sandofan M-8 or Ridomil plus, at the recommended rate of each fungicide
when the first disease symptoms appeared and.t 15 days intervals, gave low downy
mildew infection and high seed yield when compared with the check plots.