Control of trunk diseases by protecting new pruning wounds, and by trunk
Our long-term goals are to increase the options and cost-effective measures for control for grapevine cankers/dieback. In our current collaboration with Sutter Home vineyards in Arbuckle CA, we have determined that vines that historically would have been diagnosed with ?Eutypa dieback? are actually primarily infected by pathogenic strains of the fungus Botryosphaeria obtusa. Similar to Eutypa lata, B. obtusa, at least primarily, infects through pruning wounds. Last year, we surveyed paints for use as protectants, and selected for those with high elasticity (i.e., are less likely to crack), ?breathability? (i.e., presumably less likely to build up mold under the painted surface), durability for exposure to uv light and rain, and fungal-resistance.
We had excellent results last year in both the laboratory and the field with Duration Exterior Paint (Sherwin-Williams), a ?self-priming? paint; we demonstrated it was non-phytotoxic, and even allows shoot out-growth if it?s accidentally painted over a bud. Moreover, it forms a film on freshly-cut surgical and pruning wounds on grapevines in the field that prevents fungal penetration for our current one-year study period, and we predict, for the remaining life of the vines. The California Department of Pesticide Regulation (CA DPR) indicated that Duration ?would be considered a physical barrier and would not require registration as a pesticide.? A Fusarium lateritium biocontrol formulation and an inferior paint were also included in our trials, but were deemed insufficiently impressive after year one, and have been discontinued.
In addition to selection of Duration for long-term testing, we have developed a pruner that dispenses the paint during pruning. In order to determine the extent to which the Duration paint will reduce spur death and improve vine productivity in comparison to untreated controls, the industry needs a long-term trial. To this end, in collaboration with Sutter Home vineyards, vines with symptoms of dieback (i.e., at least one dead spur) were surgically cut on the trunk in February of 2005. The surgical cuts were either treated with Duration or not, and new cordons were trained; our results show that new growth has been excellent. We have proposed to continue and expand this project with treatment (or not in the untreated controls) of all pruning cuts on these vines with Duration for the next several years until assessments can be made of spur death and vine productivity in aregenerated vineyard.
For part of our project last year, we examined grapevines for insights into the life cycle of B. obtusa. Results that will be useful in developing an efficacious control strategy include the following. We observed relatively few B. obtusa pycnidia (the spore-bearing structures) on the intact vines. However, shoots were asymptomatic but infected, and after prunings were dropped to the ground, pycnidia were produced. Consequently, we propose to further examine whether prunings on the ground are an important source of inoculum. In regenerated one year-old vines, we had shoot infection occur in the spring, and consequently the infection period may be longer than previously assumed. Finally, we developed a new spore trap device for rainstorm-splash disseminated spores.
