Downy Mildew, Powdery Mildew, Black Rot, and other diseases pose an annual threat to grape production in Wisconsin. The yearly battle to control these diseases, combined with a lack of extension material addressing the disease susceptibility among cultivars, has led to several important questions within the industry in recent years: Are there any cultivars that should be avoided in our climate? Are there any cultivars that should be avoided in low-spray or organic systems? Can we trust the susceptibility ratings found in existing extension material?

As part of the Northern Grapes Project viticulture team, we are entering the second season of a two- year project directed toward gaining new insight on disease susceptibility in these cold-climate grape cultivars. During the 2015 growing season, two identical vineyards were studied, one in Sturgeon Bay, WI at the Peninsular Agricultural Research Station (PARS) and the other in Madison WI, at the West Madison Agricultural Research Station (WMARS), USDA zones 5a and 5b respectively. No fungicides were applied at either site, and weekly disease ratings and photos of each vine were taken from bud break through harvest.

Not surprisingly, our work from 2015 indicates that there is a significant difference between cultivars in disease susceptibility throughout a growing season. We also found evidence of a difference between foliar and fruit disease susceptibility, a distinction that is not made in most existing extension literature. While the first season of data indicates cultivar selection may be useful as a tool for combating disease, a second year of data will provide further information, as well as useful disease data and images that can be used by growers over the course of the 2016 growing season.

A third vineyard site is being added at PARS this season, allowing more ratings and images to be collected. With the addition of this third field site, we have an excellent sampling of the cultivars grown here in Wisconsin. This season we will be able to provide information regarding Petite Pearl, Marechal Foch, Leon Millot, Frontenac, Frontenac Gris, LaCrosse, La Crescent, St. Croix, Brianna, Marquette, and Valiant. As in 2015, sites will be scouted weekly and images of each cultivar will be collected.

During the upcoming 2016 season we will be providing regular updates in the Wisconsin Fruits Newsletter discussing disease progression on the cultivars included in our work, particularly emphasizing pictures useful in diagnosing important vineyard disease over the season. We anticipate regular updates on Downy Mildew, Powdery Mildew, and Black Rot. We will also report on additional diseases that appear in any of our test sites, and discuss appropriate action for management. We aim to provide a regular summary of disease findings at both sites to date and a discussion of appropriate action. These publications will be designed to provide an additional resource to help in decision making and disease identification throughout the season. We hope that our photos, observations, and management information will be valuable to growers as they scout their own vineyards.

This article was posted in Disease, Grapes and tagged David S. Jones, disease, grape pathology, Grapes, pathology, Patty McManus.