POPULATION-DYNAMICS OF EPIPHYTIC MYCOFLORA AND OCCURRENCE OF BUNCH ROTS OF WINE GRAPES AS INFLUENCED BY LEAF REMOVAL

Population dynamics of epiphytic fungi associated with the summer bunc h rot complex of five wine grape (Vitis vinifera) varieties in commerc ial vineyards in the San Joaquin Valley of California were monitored e very two weeks by berry washings during 1989-1992. Vines in the five r eplicated experiments were subjected to basal leaf removal or left una ltered, Although numerous genera of fungi were isolated, species of Cl adosporium, Aspergillus, Penicillium and Alternaria predominated. Popu lation densities of most fungal taxa increased at or after veraison. L eaf removal in the fruiting zones of bilateral cordon-trained vines ge nerally reduced (P < 0 . 05) mid to late season numbers of epiphytic m ycoflora; species of Penicillium, Botrytis and Aspergillus were most c ommonly reduced. Populations of Alternaria spp. and yeasts were not co nsistently affected by leaf removal. Numbers of fungi were no lower on berries when leaves were removed from both sides of vines than when l eaves were removed only from the shaded side, Incidence and severity o f bunch rots (sour rot, rots caused by Botrytis cinerea, Aspergillus n iger, and total rot) at harvest were consistently reduced where leaves had been removed in comparison to vines where no leaves were removed. In one experiment, berries from vines sprayed with the grower's choic e of pesticides at 50% or 100% of label rates had similar numbers of e piphytic mycoflora in both cases frequently lower than those from unsp rayed controls, There was a significant interaction between chemical r ate and leaf removal on the incidence of sour rot at harvest, Timing a nd extent of leaf removal did not affect population dynamics of epiphy tic fungi, or incidence or severity of bunch rots (P < 0 . 05) at harv est in other trials.