May 15, 2015
I have received several requests for information on organic disease management in Vermont vineyards. I must say from the beginning that organically-certified options for managing some diseases are very limited. For some diseases, primarily powdery mildew and to some degree downy mildew, organic options are available to manage the disease fairly well. However, for phomopsis, anthracnose, and especially black rot, you will face an uphill battle. This does not mean it cannot be done, but expect significant frustration.
The first line of defense for organic disease management is strict vineyard sanitation. This entails removal of all diseased and dead wood during pruning and removal of spur stubs (blind or dead wood on spurs beyond the point where shoots emerge in spring) after bud break. It is too late in this season to apply now, but a dormant application of liquid lime sulfur may reduce inoculum for some diseases, however this material is unpleasant to apply (to put it mildly), as it is extremely caustic to applicators and equipment and requires much care in its use. During the growing season, removal of diseased berries and clusters must be completed on a regular (i.e. weekly) basis. Application of biological or (more effectively) mineral-based copper and/or sulfur fungicides will be required in most vineyards on a regular 7-10 day schedule, season-long, to reduce disease incidence on fruit and foliage. The most effective materials are copper-based products, which do not degrade and will accumulate in the soil.
Coming from a background in apple production, where disease management typically requires 8-12 applications of synthetic fungicides for disease management, I have been encouraged by the reduced spray schedule of as few as four sprays of conventional/non-organic materials that may manage disease in grapes. However, organic disease management will require many more applications in the vineyard to produce reasonable results. Growers who pursue this strategy should refer to the 2014 Cornell Production Guide for Organic Grapes, and prepare to be vigilant in vineyard sanitation and application of mineral and/or biologically-derived products whose efficacy is questionable.