Evaluation of Phosphonate, Fosetyl-Al and Several Phenylamide Fungicides for Post-Infection Control of Grapevine Downy Mildew Caused by Plasmopara Viticola.

Abstract

Post-infection efficacy of phosphonate for the control of grapevine downy mildew was tested in two glasshouse and one field experiment on Vitis vinifera cultivars. Significant inhibition of sporulation occurred when phosphonate was applied up to 17 days after inoculation of leaves with Plasmopara viticola. In a field experiment it reduced disease incidence, hastened the necrosis of oilspots, and delayed the appearance of oilspots of P. viticola. In two experiments, fosetyl-Al, metalaxyl, benalaxyl, and ofurace similarly inhibited sporulation and reduced disease incidence. This was the first in vivo demonstration of the control of P. viticola by phosphonate, which is now registered as the first systemic fungicide with symplastic ambimobility for P. viticola in Australia. It has potential for use in anti-resistance strategies as an alternative to metalaxyl and the other phenylamides. All fungicides tested have the capacity to reduce the rate of development of epidemics of P. viticola.