Control of Eutypa Dieback of Grapes

The ultimate objective of this research is to develop practical measures for the control of Eutypa dieback of grapevines by modifying the pruning wound so that infection cannot take place. The original five objectives were 1) investigate the potential of experimental and registered fungicides to control disease, 2) determine the mechanism by which wounds become less susceptible over time 3) determine the potential for chemicals which increase the rate of wound healing to decrease the period of susceptibility of fresh wounds, 4) screen fungi which commonly occur on wounds for their potential to inhibit germination of Eutypa and therefore control disease, 5) test for the ability of nonpathogenic fungi to increase the wound healing response of the vine. Due to progress made to date, we have terminated objectives 2, 3, and 4 and added three new objectives. Objective 6 is to determine the potential role of Central Valley cherry orchards to serve as inoculum sources for Eutypa. The second new objective (Obj. 7) is to quantify the relationship between vineyard age and incidence of Eutypa dieback. We found that wound healing was dependent on a degree day relationship, which explains why late spring pruning results in a reduced period of susceptibility to infection. Using historical yield data and current disease assessment of different aged vineyards, it was found in vineyards with susceptible varieties of grapes that peak Eutypa dieback was (90%of vines infected with 40%of the spurs diseased) after 20 years correlated with a decrease in yield commonly observed beginning at about the same age vineyard. This relationship was not found in a resistant variety. Cross inoculations resulted in typical dieback symptoms of both grapes and cherries when inoculated with Eutypa fungus originating from either host. Thus, cherry orchards in the Central Valley are a likely source of inoculum for vineyards. For ongoing research, we established two plots to determine the efficacy of Rally and multiple applications of benlate (0 and 14 days after inoculation) to control disease. Degree of control achieved will be determined in the winter of 1994. We also established two field plots to test our most promising biological control agents (2 saprophytic fungi originally isolated from wounds) at two rates. We also are conducting extensive ecological studies of the microbial community on the wound service to further increase the efficacy of the biological control agents.