Michigan grape scouting report – June 13, 2024

Essential updates on weather, vine growth, disease management and pest control. Stay informed and optimize your vineyard's health and productivity!

A grape vineyard.
Photo by Esmaeil Nasrollahiazar, MSU Extension


Click the following links for detailed seven-day forecasts for various grape production regions.




See the latest agricultural weather outlook from Jeff Andresen, Michigan State University state climatologist.

Report on growing degree days (GDD)

The following table summarizes the GDD base 50 degrees Fahrenheit for the current week and the previous week, as well as the accumulated GDD for each location.

Michigan grape growing regions

Current GDD 50 F

GDD 50 F last week

Collected the past week

Benton Harbor (SWMREC)












Average for southwest Michigan








Average for southeast Michigan




Old Mission








Traverse City (NWMHRC)




Average for northwest Michigan




Vine growth

Southwest Michigan is experiencing an extended bloom period due to the winter cold damage and spring freeze event. On primary shoots, juice grapes and most hybrids have completed bloom. Some early hybrids like Marquette (Photo 1) and Brianna are at buckshot berry. Vinifera with good primary shoots are blooming or just finishing bloom. Hybrid wine grape and juice grape secondary shoots are blooming now. Secondary shoots of vinifera are up to a week or more from bloom.

A cluster of grapes hanging from a tree.
Photo 1. Marquette grapes at buckshot. Photo by Michael Reinke, MSU Extension.

In northwest Michigan, significant developments are seen in the vineyards (Photo 2). Clusters on all vinifera cultivars are expanding. The shoot length varies depending on the cultivar, with later budburst varieties like Pinot Gris and Merlot ranging from 6 to 10 inches. In contrast, earlier budburst cultivars like Chardonnay, Pinot Noir and Sauvignon Blanc measure between 15 and 20 inches.

Grapes hanging from a vine.
Photo 2. Blaufränkisch grape. Photo by Esmaeil Nasrollahiazar, MSU Extension.

In the Tip of the Mitt region, despite a brief period of cool weather this past week, abundant sunshine and moisture have fueled exceptional growth across the vines. Hybrid cultivars, like the Zweigelt from Folklor Wine and Cider in Charlevoix, Michigan (Photo 3), are particularly impressive, boasting 12 to 14 well-separated leaves with well-developed inflorescences. Vinifera varieties are following closely behind, averaging 10 to 12 separated leaves with developing inflorescences, as seen in the LaCrescent from Petoskey Farms Vineyard and Winery (Photo 3).

This encouraging progress is further bolstered by the fact that disease pressure remains low and rose chafer sightings have been minimal thus far. However, shoot thinning should be completed soon to ensure optimal vine health. The Itasca from Petoskey Farms Vineyard and Winery (Photo 3) exemplifies the overall positive development across the vineyard.

Three different types of grape varieties.
Photo 3. LaCrescent, Zweigelt and Itasca varieties. Photo by Derrick Vogel, Folklor Wine and Cider.

See this chart for grape growth stages.


In vineyards in southern Michigan, many growers are bringing new shoots up from the base of the vines to replace older or damaged trunks and cordons as a result of the past winter. In these cases, very little trunk cleaning or shoot thinning is currently being done. In some cases, new canes that were laid down during last winter have been brought up for new trunks and cordons. In these vineyards, some shoot thinning and trunk cleaning has been completed. Shoot thinning and trunk cleaning should be underway in many varieties in northern vineyards.

Shoot thinning plays a crucial role in canopy management, offering multiple benefits such as enhanced air circulation, reduced disease susceptibility, minimized shading, improved spray penetration and, ultimately, elevating fruit quality during the harvest period. It is advisable to perform shoot thinning when the shoots reach a length of 5-12 inches, ensuring they are still easily breakable from the woody tissues.

For more comprehensive information on shoot thinning and other early season vineyard management practices, please refer to the Michigan State University Extension article, "Early Season Vineyard Management."


During this time of the year, the primary diseases of concern for grape growers are phomopsis, black rot, anthracnose and powdery mildew. If you're seeking detailed insights into prebloom fungicide options and the effects of rain on disease spread, we recommend referring to an earlier grape scouting report or exploring an article on early-season disease management.

It's worth noting that some growers have recently observed isolated cases of downy mildew infections in northern vineyards. Southern vineyards have been seeing early infections of phomopsis and are beginning to see black rot lesions.

As bloom continues in southwest Michigan, start choosing fungicides that control all the fruit diseases. For example, with downy mildew we are most concerned with fruit infection at this time and sprays should be timed prior to bloom and at bloom for optimal control. Downy mildew is caused by a fungal-like organism, so many site-specific systemic fungicides that target other spring diseases do not work on downy mildew. Effective fungicides for downy mildew include products in FRAC codes 4, 11, 21, 40 and 45 as well as phosphorus acid salts and some biologically-based products.

With the exception of powdery mildew, these spring disease infections typically require rain events. It only takes 0.1 inches of rain above 50 degrees Fahrenheit to trigger a possible infection. Viticultural practices that reduce canopy wetness such as good irrigation timing, leaf removal and good weed management can reduce many of these diseases in a vineyard. Typically, DMIs (FRAC 3), captan and EBDCs (FRAC M3) are effective for phomopsis, black rot and anthracnose.


First generation larvae of grape berry moth have been detected in grape clusters in recent weeks in SW Michigan. Based on the degree day model for this pest, the start of the second generation egglying is expected in late June/early July in SW Michigan, proceeding later into July at further north locations. Also, the first sightings of grape tumid gallmaker infestation, and the first rosechafers, were detected last week in SW Michigan. Potato leafhopper has also been found in grape vineyards and is active across the state from recent spring invasion on warm winds from the south (Photo 4). Protect susceptible cultivars, especially in young vineyards where PLH can stunt shoot growth. Neonicotinoid insecticides such as Assail and Admire Pro can provide protection against PLH, rosechafer, and tumid gallmaker if present in the same vineyard site.

Potato leafhopper on a grape leaf.
Photo 4. Potato leafhopper. Photo by Cheyenne Sloan, MSU Extension.

Call to action

The Sustainable Agricultural Management (SAM) Tool is a comprehensive software application designed to assist grape growers in managing vineyards more effectively. Please sign up to access the SAM Tool. The application is developed by Karen Chou of Michigan State University (MSU) Extension in collaboration with MSU’s Department of Computer Science and Engineering. Dennis Phillips is the lead software developer.

The application offers a range of features designed to save time and enhance vineyard management efforts. It employs robust data security and accuracy measures and can be used for mapping sub-fields, generating auto-populated spray records, and issuing warnings about the consecutive use of the same pesticides to minimize the development of pesticide-resistant pests.

Additionally, the app displays your spray tasks on a calendar and helps to identify restricted entry fields and manage preharvest sprays using the restricted-entry interval and preharvest interval databases. It also facilitates task assignments, sends task reminders for managers and workers, and allows the upload of photos and scouting notes directly from the field, which can be viewed later within the application.

You can also help the Michigan Wine Collaborative pilot the Michigan Vine Balance Workbook, a sustainability certification program, through the website. Please fill out this brief survey to answer one question and enter your contact information for Chou to offer you personalized guidance on beginning to use this application.

Upcoming events

Parallel 45 Vines & Wines Pre-Veraison Meeting: Boost Grapevine Productivity. Gain valuable insights from industry experts at our upcoming hybrid meeting on July 12. We'll focus on presentations about compost tea, biochar and organic compost from Krull's. Don't miss out – pre-registration is required!

The 35th annual Michigan Viticulture Field Day and inaugural Michigan Enology Experience are approaching. MSU’s famous field day and steak dinner is back on July 31. We are now adding a second day just for the winemakers.

Dirt to Glass™ 2024: Elevating Michigan Wine from the Ground Up, Aug. 22-23. Dirt to Glass aims to connect growers and producers each year and provides information to support the Michigan grape and wine industry in understanding the critical relationship between better farming and world class wine.

As a collaboration between Michigan State University, Michigan State University Extension and industry innovators and educators, this groundbreaking event disseminates the most current research and cutting-edge practical information to elevate the grape and wine industry.

This year's conference will continue the journey started in 2022, aiming to elevate the Michigan grape and wine industry through a deeper understanding of soil health and fertility, carbon cycle and sequestration, and soil-vine interaction, all crucial sustainability elements in producing high-quality grapes and wines from vineyard to economic sustainability. Each technical session will be complemented by wine educational sessions.


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