Evaluation of Pruning Wound Susceptibility and Protection Against Fungi Associated with Grapevine Trunk Diseases

Abstract

Trunk diseases diminish vineyard longevity and productivity in nearly every raisin, table, and wine grape production region worldwide. Fungi causing these diseases infect primarily through pruning wounds. One way to control these diseases is to protect pruning wounds with fungicide applications, which can be problematic because of the limited number of registered products; the difficulty for these products to control numerous taxonomically unrelated organisms; the challenge of these products to protect for the entire period of wound susceptibility; and the difficulties and costs associated with hand application of protection treatments. Our goal was to compare the susceptibility of grapevine pruning wounds to various fungi associated with trunk diseases and to evaluate the efficacy of selected fungicides to control these pathogens when applied as pruning wound protectants. The study was conducted over two consecutive years in two separate vineyards in Sonoma and Colusa counties, California. Nine pathogenic fungi were tested: Eutypa lata, Botryosphaeria dothidea, Diplodia seriata, Dothiorella viticola, Lasodiplodia theobromae, Phaeomoniella chlamydospora, Pleurostomophora richardsiae, Togninia minima, and Phaeoacremonium parasiticum. Results showed differences in the infection rates of pruning wounds by these fungi. Species of Botryosphaeriaceae were the most infectious, T. minima, P. parasiticum, P. richardsiae, and E. lata were less infectious, and Pa. chlamydospora was intermediate. Four selected fungicides were tested: 1% Topsin M, Biopaste (5% boric acid in a wound-sealing paste), 1% Cabrio EG, and Garrison. Although results highlight the difficulty of these products to control the entire spectrum of pathogens efficiently, Topsin M was overall the most efficacious product.