Effect of grapevine training systems on susceptibility of berries to infection by Erysiphe necator

The effect of two training systems on the development of powdery mildew caused by Erysiphe necator in berries of Chardonnay and Cabernet Sauvignon grapevines was examined. Disease development was monitored on berries from vines trained to either vertical shoot positioning or as free-positioned, topped vines with no foliage support wires. No fungicides were applied and powdery mildew development was recorded following artificial inoculation of young berries. Disease incidence was higher in berries collected from the vertical shoot system than in berries from the free-canopy vines. Incubating the berries under the reciprocal training system had a slight effect on PM development with the more susceptible berries of the VSP system but not on berries from the free canopy. The data suggest that the training system decreases disease development mainly through an effect on the susceptibility of the berries. The latter were less vulnerable to artificial inoculation performed in the laboratory after prior exposure to higher radiance intensity. The free-position system may therefore be useful in reducing the use of fungicides.