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University of Minnesota Extension Grape Crop Update

Grapes in the southern half of Minnesota are moving along quickly, many ranging from 4-6 in. tall showing clusters at the bud stage.
Canopy management
At this growth stage, shoots are still tender enough to be removed by hand. Cold climate grapes are typically thinned to 6-8 shoots per linear foot of canopy. Secondary shoots can also be thinned. Secondary shoots are visible when there are two shoots emerging out of the same node (see picture below), in which their emergence is more common in some cultivars than others.
Photo showing primary (P) and secondary (S) buds emerging from a single node on a Concord grapevine cane. The arrows indicate the direction each shoot will grow. Often times, the secondary shoot will be at a 45 degree angle, but this is not always the case. Photo taken at Firefly Berries on 05/07/2024 (Zone 4a). Note: the woody shoot branching from the cane at the same node is a lateral shoot that can be pruned.
Diseases
Growers can continue routine conventional or organic fungicide spray programs to proactively manage fungal pathogens at this time. To learn more about grape diseases and appropriate fungicides to apply, refer to the Midwest Fruit Pest Management guide.
A grape leaf showing early signs of Grape phylloxera (Dactylosphaera vitifoliae) galls, circled in yellow.Photo taken at the UMN Horticultural Research Center, near Chaska, Minnesota (Zone 5a; photo taken by John Thull- UMN HRC Vineyard Manager).
Insect pests
 
Grape phylloxera: The UMN Horticultural Research Center reported some early signs of Grape phylloxera (Dactylosphaera vitifoliae) on grape foliage.

About:

  • Grape phylloxera is an insect pest that can affect both the roots and foliage of grapes, but most cold climate interspecific hybrid grapes grown in Minnesota are mostly susceptible to foliar damage.
  • Grape phylloxera exhibits multiple generations per growing season and the first generation, known as “crawlers”, emerge in the spring from mother eggs on the trunk and cordons and migrate to the newest grape foliage, potentially leading to 40-50 galls per leaf. Thus, the University of Minnesota recommends managing the crawlers as the most critical management stage, especially when growing more vulnerable cultivars like Frontenac.
  • For vineyards with an extensive history dealing with Grape phylloxera, time insecticide applications during early gall detection. UMN Extension recommends conventional growers use Danitol (pyrethroid) or Movento (systemic) for conventional grape phylloxera management. To learn more about grape phylloxera and management, visit this UMN webpage and refer to the Midwest Fruit Pest Management guide. — By Madeline Wimmer, University of Minnesota Extension Educator

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