Biology, Epidemiology and Control of Cladosporium spp. on Pinot Noir

Twelve fungicides, of different chemistry, were tested, each at two different rates for the control of Cladosporium spp. Eleven of the fungicides are currently registered for grape and one in the process of being registered. Two fungicides, Stratego & Switch, belonging to different fungicide families were found to effectively kill Cladosporium spp. Based on poison agar assays. Three other fungicides, Bravo, Maneb, and Ziram, also controlled the fungus, but the degree and duration of control was less pronounced when compared to Stratego and Switch. The seven other fungicides did not provide any significant Cladosporium spp. Control.Field spray trials were conducted, to test six different fungicides, in Santa Rosa-Chardonnay and Santa Rosa-Pinot Gris. We examined their ability to affect Cladosporium spp. Populations on grape clusters after one application around verasion. We found two fungicides, Flint and Elevate that produced statistically significantly decreases in the fungal populations. The four other fungicides had no effect on fungal population. The population survey showed how Cladosporium spp. Population changes from bloom to harvest, depending on location and variety. In North Coast vineyards, which includes Santa Rosa-Chardonnay, Santa Rosa Pinot Gris, and Sebastopol-Pinot Noir, we initially saw low, steady populations of Cladosporium spp. However, between mid June and late July, we saw an exponential increase in the fungal population. This was followed by a change in Cladosporium spp. Population; it became either stationary or decreased. The population data also showed that a large population of Cladosporium spp. Existed on berries prior to any signs of infection. This information advises future research on the timing of fungicide sprays. The large decrease in Cladosporium spp. Population in the Santa Rosa vineyards in late July cannot be correlated to any chemical application, but may be related to temperature, humidity or varietal effects. We observed that Cladosporium spp. Preferentially grew on clusters as compared to leaves. In the Carneros vineyards we saw a steady state in terms of the number of populations of Cladosporium spp. At bloom and harvest, which were also significantly lower than the North Coast vineyards. However, we did see a relatively large decrease in the Carneros-4 Pinot Noir vineyard from early June to mid July, and we did not see this decrease in Cladosporium spp. Population in the Carneros-7 vineyard. This may have been due to several factors, including temperature and humidity. Carneros-4 and 7 are the same Pinot Noir clone and on the same hill but the slopes face different directions. Carneros-4 has a Southeast-facing slope, while Carneros-7 has a Northeast-facing slope. The decrease in fungal number in Carneros-4 may also be due to unknown chemical applications; we have been unable to obtain spray records for the Carneros sites, though we are still trying.The population and temperature growth profile data suggested that in seasons with many cool days, greater then 5C and less then or equal to 25C, during the bloom to harvest time period, may result in increased disease pressure, while prolonged temperatures of 30C or higher is detrimental to fungal growth. Finally, using weather data, we hypothesize that humidity may play a pivotal role in disease incidence and severity.Cladosporium spp. grew little or slowly at temperatures at or above 30C, or at or below 5C. It grew well at 10-25C. Fungal growth increased when the Cladosporium spp. fungi were inoculated on a berry skin based media compared to PDA, and a berry pulp based media. This suggests that the berry skin may be a preferential substrate for this fungus. Also, from microscopic observations, no fungal sexual reproductive structures have been found. The fungus has septate hyphae and asexual reproduction occurs rapidly, often in 1-2 days, on PDA over a wide temperature range.