Differences in grape phylloxera-related grapevine root damage in organically and conventionally managed vineyards in California

Abstract

Secondary infection of roots by fungal pathogens is a primary cause of vine damage in phylloxera-infested grapevines (Vitis vinifera L.). In summer and fall surveys in 1997 and 1998, grapevine root samples were taken from organically (OMVs) and conventionally managed vineyards (CMVs), all of which were phylloxera-infested. In both years, root samples from OMVs showed significantly less root necrosis caused by fungal pathogens than did samples from CMVs, averaging 9% in OMVs vs. 31% in CMVs. Phylloxera populations per 100 g of root did not differ significantly between OMVs and CMVs, although there was a trend toward higher populations in OMVs. Soil parameters, percent organic matter, total nitrogen, nitrate, and percent sand/silt/clay also did not differ significantly between the two regimes. Cultures of necrotic root tissue showed significantly higher levels of the beneficial fungus Trichoderma in OMVs in 1997 but not in 1998, and there were significantly higher levels of the pathogens Fusarium oxysporum and Cylindrocarpon sp. in CMVs in 1998 but not in 1997. Implications for further research and for viticulture are discussed.