Biotic and abiotic factors associated with grape root borer (Lepidoptera: Sesiidae) infestations in Virginia vineyards

Grape root borer, Vitacea polistiformis (Harris) is an oligophagous and endemic pest of grapevines in portions of the eastern United States. Larvae feed on roots of wild Vitis species and commercially important Vitis species and rootstocks, posing a significant threat to vineyard health and productivity under some circumstances. Season-long infestation status surveys based on weekly pupal exuviae sampling in Virginia vineyards from 2008 to 2012, revealed that the 50 blocks surveyed varied substantially in this regard, ranging from heavily to lightly infested. There has not been a comprehensive assessment of the biotic or abiotic factors underlying this variation and the objectives of this study were to identify key risk factors associated with grape root borer infestations and to develop a predictive model. Horticultural (cultivar, rootstock, vine age, block size, proximity to wild grapevines), cultural (insecticide use, ground cover, weed control, irrigation) and environmental variables (soil texture, moisture, pH, organic matter, bulk density, cation exchange capacity) were measured in each vineyard block and included in the model. Variable data (nominal, ordinal, and continuous) were subjected to optimal quantification using Categorical Principal Component Analysis (CATPCA). CATPCA was used to reduce the number of original variables to a few uncorrelated principal components which were used in multiple regression to develop a relationship between vineyard factor and level of grape root borer infestation. Results are discussed in relation to the degree of infestation among Virginia vineyards and the potential implications of a predictive, risk assessment model for commercial vineyards.