Effects of spray adjuvants on grape (Vitis vinifera) berry microflora, epicuticular wax and susceptibility to infection by Botrytis cinerea

Spray adjuvants were tested for their effects on epicuticular wax morphology, grape berry microflora and susceptibility of berries to Botrytis cinerea on Chardonnay, Shiraz and Cabernet Sauvignon cultivars. The four adjuvants used in this trial altered epicuticular wax morphology. Disintegration of the wax platelets was least for the wetter-spreader recommended for sensitive crops, and greatest for the crop oil concentrate and the activator-penetrant. Waxes did not regenerate over the season after treatment with the adjuvants. A cyprodinil/fludioxonil fungicide was effective at controlling B. cinerea infection, but when combined with an adjuvant, was less effective in the three grape cultivars. Irrespective of whether a fungicide was used, adjuvant application resulted in lower yeast and fungal populations on Chardonnay berries. There were no effects of the adjuvants on the microflora of Shiraz and Cabernet Sauvignon berries, except for the crop oil concentrate which resulted in higher bacterial populations on Cabernet Sauvignon berries. We hypothesise that spray adjuvants increased the susceptibility of grape berries to B. cinerea through epicuticular wax alteration and, in some circumstances, through the reduction of the indigenous microflora on the berry surface.