3.7.60
CONTROL OF POWDERY MILDEW OF GRAPES (OIDIUM TUCKERI) WITH ULTRA FINE SUN SPRAY MINERAL OIL

JR MONTEALEGRE, JL HENRIQUEZ, W LIRA, G VASOUEZ, H MERY and X CHAVEZ

Dept. Sanidad Vegetal, Facultad de Ciencias Agrarias y Forestales, Universidad de Chile, Casilla 1004, Santiago, Chile

Background and objectives
Powdery mildew of grapes in Chile is one of the most important diseases, affecting both table and wine cultivars. Its control is generally obtained with sulphur or IBE fungicide sprays. The use of mineral oils against powdery mildews as a different alternative to the actually existing fungicides to control this disease has been studied by Pearson and Riegel [1] and Northover and Schneider [2]. In this line, the Department of Sanidad Vegetal of the University of Chile and Sun Company, Inc., have conducted research from 1993 to date on the uses of Ultra Fine Sun Spray Mineral Oil (UFSS), to determine its mode of action and efficacy, optimum dosage of application, uses in mixture with IBE fungicides to increase persistence and diminish risk of selecting strains of this fungus resistant to these fungicides, the effects on berry sugar contents, and toxicity to diverse table and wine grape cultivars.

Results and conclusions
We determined that UFSS act as an artificial protecting barrier on the plant organs, inhibiting or difficulting the infection by 0. tuckeri>/i>, destroying also directly the fungus conidia and hyphae when applied onto established infections. UFSS also has preventative, curative and erradicant effects of such infections, having and effect better than sulphur, and comparable with that of IBE fungicides such as fiuzilasol or myclobutanil. The optimum UFSS concentration to control powdery mildew of grapes is 1% (0.5-1.0%). When mixed with myclobutanil, UFSS increases the persistence of this IBE fungicide and diminishes the risk of appearance of resistant 0. tuckeri strains, achieving also a very good control of the disease with only 4 sprays during the season, compared with the 7 or more sprays needed when using only sulphur or IBE fungicides. Berries harvested from plants treated with UFSS showed no decrease in sugar contents. With respect to the phytotoxic effects on diverse table and wine grape cultivars when applying UFSS followed by incompatible fungicides like sulphur or captan, Thompson Seedless was the most susceptible cultivar, followed by Merlot, Red Globe, Cabernet Sauvignon, and Chardonnay. The waiting period between a spray of UFSS and another of sulphur or captan must be at least 20 days. It is concluded that UFSS is another tool to control 0. tuckeri on table and wine grape cultivars, applied alone or in mixture with an IBE fungicide, increasing its persistence and diminishing the number of sprays during the season, and the risk of appearance of strains resistant to IBE fungicides.

References
1. Pearson RC, Riegel DG, 1993. Fungicide and Nematicide test 48, 79.
2. Northover J, Schneider KE, 1996. Plant Disease 80, 544-550.