Evaluation of the efficacy of seed treatments against Plasmopara halstedii.
Downy mildew caused by Plasmopara halstedii is an economically important disease of sunflower. The risk of damage is particularly high in a damp spring. As there are no genetically resistant sunflower cultivars, seed treatment with a systemic product appears to be the only solution for control. This study was carried out to analyse, under growth-chamber conditions and in the field, the effectiveness of 11 fungicides applied as seed treatments. Only combinations including metalaxyl or oxadixyl gave good control of P. halstedii. These fungicides gave total protection, without phytotoxicity, at 2.5 g of commercial product kg-1 seed for 10% metalaxyl + 48% mancozeb, and at 3 g kg-1 seed for the combinations 10% oxadixyl + 56% propineb and 8% oxadixyl + 56% mancozeb + 3.2% cymoxanil.