Physical Modes of Action of Petroleum and Plant Oils on Powdery and Downy Mildews of Grapevines

Abstract

Three petroleum (mineral) oils and two glyceridic plant oils, applied as emulsions (1% vol/vol) in water, were compared with reference materials for the control of powdery mildew on potted vines of Vitis vinifera cv. Chardonnay under greenhouse conditions. The same materials were tested at 15 liters of oil/1,500 liters of water/ha in five-application programs in vineyards of V. vinifera x labrusca cvs. New York Muscat and Canada Muscat. In a series of greenhouse experiments, the petroleum oils provided moderate protection, excellent pre-lesion and post-lesion curative action, and were antisporulative. The plant oils showed significant action only in pre-lesion treatments and as antisporulants in treatments applied to established lesions. In the vineyard, the petroleum oils, Stylet-Oil, Sunspray UFO, and Safe-T-Side, were as effective as myclobutanil (Nova) in suppressing powdery mildew. Canola and soybean plant oils, emulsified with Agral 90, were no better than Agral 90 alone, and reduced the incidence of disease only marginally in comparison with a water check. Potted Chardonnay vines were inoculated with downy mildew and treated one day pre- or one day postinoculation with Sunspray UFO, safflower plant oil, mancozeb, or water. Only the preinoculation application of mancozeb reduced the incidence of downy mildew. Three petroleum oils and two plant oils were inefficacious against downy mildew in vineyard experiments.