Grape foliar and fruit diseases: Early-season management

Article written by Madeline K Wimmer, UMN Extension Fruit Production Educator.  Infographic: Early-season grape diseases are often managed proactively before infections occur. Above are the top five pathogens to be aware of during early-season management. Disease symptoms can vary in appearance based on the severity of infection, and the grapevine growth stage, varietal type, and other factors. Infographic created by Madeline Wimmer, UMN Extension Fruit Production Educator.

In the Upper Midwest, where rainy springs and humid summers are common climatic features, grapevine foliar and fruit diseases become a large part of pest management planning. There are a number of different diseases that infect grapes, some that can more severely affect fruit quality and crop yield. The five main pathogens managed during early-season vineyard management include phomopsis cane and leaf spot (Phomopsis viticola), anthracnose (Elsinoe ampelina), downy mildew (Plasmopara viticola), black rot (Guignardia bidwellii), and powdery mildew (Uncinula necator). Disease symptoms of these pathogenic infections may not immediately appear, or progress to the point of concern during this time. However, many pathogens do begin infecting plants early-season from bud break until berry set, especially during and after rain events. 

Because of this, it’s recommended to take a proactive approach to managing grapevine foliar and fruit diseases, as post-infection treatments are often limited in options and their effectiveness. 

 

Removing infected materials

Many pathogen spores overwinter in fruiting bodies (similar to microscopic mushrooms) on remaining fruits, mature shoots (i.e. canes), and older wood (i.e., old spurs, cordons, and trunks). Proactive management starts with removing infected materials away from a vineyard, or destroying them on site to reduce the total spore count in the vineyard. This includes removing mummified grape clusters and pruning wood, which is often burned or repurposed off-site. Wild grapevines growing near the perimeters of a vineyard can also be removed as they can passively host various diseases.

Pruning and canopy management:

How well grapevines are pruned and managed throughout the summer determines shoot density for each grapevine canopy, which impacts how well air flows throughout the canopy. 

Many pathogen spores thrive in high humidity conditions and long periods of leaf/fruit wetness to cause an infection. Thus, following pruning with early season shoot thinning can ensure adequate shoot density. 

Additional practices like exposing fruit clusters by leaf removal, as well as secondary and/or lateral shoot removal are two ways to also encourage clusters to dry faster after rain events and increase their exposure to any organic or conventional pesticide product being applied.

Fungicide programs:

Fungicides that adhere to conventional and USDA Organic regulations exist to proactively manage and, in some cases, treat grapevine diseases. Grapevine conventional fungicide programs are thoroughly covered in the Midwest Fruit Pest Management Guide starting on page 136. Growers who manage their vineyard under USDA Organic standards may apply sulfur or copper products as a part of a fungicide program for grape varieties that do not exhibit sensitivity. Copper specifically can also cause injury to tolerant vines when applied during hot conditions. All growers should take time to understand fungicide classifications to prevent fungicide resistance. The Midwest Fruit Pest Management Guide lists general fungicide effectiveness against various pathogens, along with other important information that can be found on product labels. 

Information in this publication is for educational purposes only.