THE INFLUENCE OF SOIL PROPERTIES ON THE DEVELOPMENT OF GRAPE PHYLLOXERA POPULATIONS IN AUSTRIAN VITICULTURE

Over a period of four years, different study sites were monitored by sampling roots and soil. To assess the possible influence of soil characteristics on phylloxera infestation, in addition to the monitoring of nodosities on rootlets, chemical and physical soil properties were analysed. Furthermore, the structure, porosity and water permeability were described for some study sites. A significant correlation between phylloxera infestation and several soil properties could be stated. Permanent soil properties like pH, carbonate content, organic carbon (C_org) and soil texture had an impact on phylloxera infestation. The soil pH of the investigated vineyards ranged from 5.0 to 7.8 and was negatively correlated with phylloxera infestation. With increasing clay and humus content, the abundance of nodosities increased. The specific formation of clay humus complexes, being a very important part of the micro structure of the soil, might be the main factor enhancing the infestation. The sand and carbonate contents of the soil had a negative effect on the infestation. Phylloxera infestation was also closely related to the nutrient availability, especially of phosphorous, potassium, magnesium, copper and zinc. Furthermore, a highly significant correlation between infestation frequency and the K/Mg-ratio could be stated. Surplus or deficiency situations for magnesium and potassium, especially in the lower soil layer, enhanced the phylloxera infestation. In contrast to other investigations, the N_min-content and the total N content did not show any correlation to the infestation. For other physiochemical soil parameters like soil type, silt content, manganese, boron and electric conductivity, but also for soil microbial parameters like soil respiration, microbial biomass, N-mineralization, soil enzyme activities (xylanase, arylsulfatase), no influence could be stated.