Michigan grape scouting report – June 19, 2024

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

Grapes blooming.
Photo 1. LaCrescent hybrid grape bloom at Petoskey Farms and Winery. Photo by Derrick Vogel, Folklor Wine and Cider.


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 (NWMHRS)




Average for northwest Michigan




Vine growth

Bloom is finished in most juice grape and hybrid blocks in southwest Michigan. Some early hybrids like Marquette and Brianna are at buckshot berry. Vinifera bloom on primary shoots is almost finished and fruit set is looking good. Vinifera varieties with secondary shoots are blooming now (Photo 2).

With bloom complete in juice grapes, growers are assessing crop estimations. The spring freeze has caused more damage than earlier expectations. The current estimate is for harvest volumes of Michigan juice grapes to be approximately 10-20% of average.

With the heat and humidity over the next week, growers are preparing for potential powdery mildew management. Spray schedules have been difficult with the high temperatures as some locations have been observing low temperatures near 80 degrees Fahrenheit and highs in the mid-90s.

Shoot positioning in wine grapes continues. Combing has begun for juice grapes.

Concord grapes in bloom.
Photo 2. Concord bloom. Note fruit set (upper portion), current bloom (lower left) and pre-bloom (lower right) on the same plant as a result of the freeze on April 25, 2024, causing substantial secondary shoot development. Photo by Michael Reinke, MSU Extension.

In the Tip of the Mitt region, hybrid cultivars are in the middle of bloom. Vinifera varieties have not begun bloom but are close. With the increased heat and humidity over the past week, disease pressure has increased. Black rot (Photo 3) as well as phomopsis are being observed. Rose chafer observations are also becoming more common. Populations have increased in some locations to the point where management has been warranted. Shoot positioning is underway, especially for vigorous cultivars.

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 LaCrescent from Petoskey Farms Vineyard and Winery (Photo 1) exemplifies the overall positive development across the vineyard.

Black rot spots on a leaf.
Photo 3. Black rot (as seen here) and phomopsis are being seen more in northern Michigan as the temperature and humidity have increased. Photo by Derrick Vogel, Folklor Wine and Cider.

See this chart for grape growth stages.


In vineyards in southern Michigan, many growers are training new shoots from the base of the vines to replace older or damaged trunks and cordons as a result of the past winter damage. 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 the 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, reducing over-cropping 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 can be found in grape clusters in southwest Michigan vineyards, especially those with low cropload that have not been treated with insecticide yet. Scouting vineyards along the edges and into blocks can quickly show whether your locations have activity of grape berry moth larvae and their stage of development. Some insects develop more slowly when it is extremely host, but we don’t yet know how to adapt the grape berry moth model for extreme heat days, so it has been accumulating heat units quickly during this warm spring.

Based on the degree day model calculations for grape berry moth, and using wild grape bloom observations from this spring in southwest Michigan to set the starting point for adding degree-days, the start of second generation egglaying is coming early. That’s not too surprising given this year’s weather. The model is predicting second generation egglaying in southern Berrien County starting around June 25 and proceeding into late June and early July at further north locations.

It is important to realize that this model predicts the start, but there will be an extended period of egglaying and larvae developing into July. Based on the conditions in your region and the vineyard cropload, consider the need for repeat applications during this period to protect clusters from grape berry moth. Products with extended activity and those with performance under high heat and sunlight conditions should be considered given this year’s weather and the extended egglaying from berry moth during the summer.

The first sightings of grape tumid gallmaker infestation and rose chafers were detected recently in southwest 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. Grape leafhoppers can also be found in their first generation on interior canopy leaves in some unsprayed vineyards. These insects need continued monitoring this season as a second generation is predicted with the warm spring. Neonicotinoid insecticides such as Assail and Admire Pro can provide protection against leafhoppers, rose chafer and tumid gallmaker if present in the same vineyard site.

Additional information

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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