Fusarium proliferatumas a Biocontrol Agent Against Grape Downy Mildew

Abstract

Postinfection applications of microconidial suspensions of Fusarium proliferatum G6 reduced sporangial production of Plasmopara viticola on grape leaf disks by 97% and prevented resporulation. Microscopic examination of the hyphal interaction in vitro showed hyphae of F. proliferatum G6 coiled around and inside sporangiophores of P. viticola. In the field from 1992 to 1995, where substantial natural grape downy mildew developed, weekly applications of F. proliferatum G6 microconidia reduced disease development on leaves and fruit clusters of Vitis interspecific hybrid cultivars Chancellor and Lakemont. Severity of downy mildew on Chancellor clusters was reduced by 77% in 1992, 80% in 1993, and 53% in 1994 and was reduced on leaves by 71% in 1992. On Lakemont, disease severity on clusters was reduced by 99% in 1993, 94% in 1994, and 81% in 1995 and was reduced on leaves by 79% in 1992, 67% in 1994, and 60% in 1995. Fumonisin mycotoxins, which are produced by F. proliferatum, including F. proliferatum G6, were not found in grape berries or juice made from berries sprayed with microconidia in the field. Agar tests with fungicides showed sulfur, copper, and metalaxyl to be minimally detrimental to F. proliferatum G6. Biological control with F. proliferatum might be practical in conjunction with a management program in which sulfur and copper are used or in an antiresistance management program with metalaxyl, on moderately resistant cultivars, or in areas where downy mildew is not severe.