Glasshouse evaluation of fungicides for the control of sunflower downy mildew (Plasmopara halstedii).
Sunflower germlings (4-d-old) were inoculated by immersion in a zoosporangium suspension of P. halstedii. Seedlings were then immersed in appropriate concn of the chemicals to be tested. Plants were grown in a greenhouse and assessed on 3 occasions to determine successively antisporulant, curative (systemic fungistatic), and eradicant effects. Sporulation in general was inhibited by lower concn than those required to exert an eradicant effect. There was a highly significant correlation between the ED50 values for visually recognised disease symptoms (stunting, damping off and leaf chlorosis) and for both curative and eradicant effects. Among 13 compounds tested, metalaxyl, RE 26745, furalaxyl, LAB 149202F and cymoxanil showed sufficient eradicant activity, to justify field evaluation for eradication of seed infections.