Michigan grape scouting report – July 16, 2025

Check out the latest Michigan Grape Scouting Report for timely updates on weather, vine growth, disease management, and pest activity. Stay informed and make proactive decisions to support vineyard health and productivity.

For decorative purposes.
Photo by Esmaeil Nasrollahiazar, MSU Extension

Weather update 

Detailed seven-day forecasts for Michigan grape production regions are available below: 

Agricultural Weather Outlook: Weekly in-season weather updates are provided to the Michigan State University Extension fruit team by Jeff Andresen, Michigan State University (MSU) agricultural meteorologist. These reports offer timely insights into weather conditions affecting fruit production across Michigan.  

Growing degree day (GDD) report 

Track vine development using the MSU Enviroweather Growing Degree Day (GDD) map. Visit the site to find your nearest weather station, create a free account, and monitor GDDs daily: MSU Enviroweather GDD Tool 

Weekly GDD summary (Base 50 F) 

The table below summarizes current GDD accumulation, last week's totals, and the weekly increase for each monitored location across Michigan: 

Location

Current GDD (Base 50 F)

GDD Last Week

Weekly Accumulation

Benton Harbor (SWMREC)

1515.9

1173.0

168.5

Fennville

1369.9

1218.4

151.5

Lawton

1504.2

1337.3

166.9

Average – Southwest Michigan

1463.3

1301.0

162.3

 

Romeo

1365.0

1186.7

178.3

Average – Southeast Michigan

1365.0

1186.7

178.3

Old Mission

1006.3

866.1

140.2

Petoskey

974.7

842.6

132.1

Traverse City (NWMHRS)

1090.9

943.7

147.2

Average – Northwest Michigan

1024.0

884.1

139.8

Weather forecast 

Last week was a seasonable but dry week. Southern Michigan experienced another week of highs in the mid-80s on most days. Northern Michigan was 5-10 degrees cooler. Once again, high humidity kept the lows in the mid-60s in southern regions and mid-50s to low 60s to the north, causing continued concern for powdery mildew infections.

Rain has been extremely variable. Last week, southwest and west central Michigan received less than a quarter inch of rain scattered across a couple of days. Southeast and northwest Michigan saw between 1 and 2 inches of rain Friday and Saturday (July 11-12). This variability has been common this year. Southwest Michigan and other parts of the state are seeing very dry soils. According to the U.S. Drought Monitor, some of the grape growing parts of the state are under drought conditions.

The forecast for the next week calls for slightly warmer conditions in northern American Viticulture Areas (AVA) and continued seasonable weather in southern locations. Most days should see high temperatures near 80 degrees Fahrenheit in northwest Michigan, mid-80s further south. A cool front is predicted to bring some precipitation Thursday, July 17, with another system moving through over the weekend. Predictions are for less than an inch of rain for the northern AVAs, up to an inch in the rest of the state.

Vine growth 

In southwest Michigan, most hybrids and juice grapes are at berry touch as are tight clustered vinifera cultivars. Leaf removal continues. The first round of cluster thinning is beginning. With concerns of harvest restrictions for juice grape growers, some Concord grapes are also being cluster thinned to improve quality at harvest.

In northern Michigan, shoot growth has picked up rapidly over the past week—shoots are now about 20 inches above the top wire, reflecting a strong post-bloom push. Most varieties are currently at bloom or just past fruit set, aligning with the modified E–L phenology stages 29–31:

  • Stage 29: Clusters hang downward, berries about 4 millimeters (mm) in diameter (pepper corn-size).
  • Stage 31: Berries reach about 7 mm (pea‑size) and bunches begin to hang.

This confirms that fruit development is progressing well. For a precise visual reference, consult MSU Extension’s Grape Growth Stages chart.

Pinot Gris grape cluster growing on a vine.
Photo 1. Pinot Gris at Mari Vineyards are thriving, with berries at pea-size stage as of July 15, 2025. Photo by Esmaeil Nasrollahiazar, MSU Extension.

In the Tip of the Mitt AVA, hybrid cultivars are in the berry touch stage and beginning bunch closure. Vitis vinifera cultivars are approaching the berry touch stage. Japanese beetle pressure is increasing. Powdery mildew and downy mildew risk is increasing. Downy mildew being noted in some vineyards.  

In southeast Michigan, fruit set looks good across the region, with most varieties approaching bunch closure. Grape berry moth trap counts in Lenawee and Macomb counties remain at zero.

There is a high risk of powdery mildew infection from July 16-18 and again from July 21-22. In addition, there is moderate risk for downy mildew and black rot conidia infections on July 17-18.

Fredonia grapes growing on a vine.
Photo 2. Fredonia grapes in Romeo, Michigan, on July 9, 2025. Photo by Derek Plotkowski, MSU Extension.
Frontenac grape cluster growing on a vine.
Photo 3. Frontenac grapes at Youngblood Vineyard in Ray Township, Michigan, on July 9, 2025. Photo by Derek Plotkowski, MSU Extension.

Horticulture 

Accurate assessment of vineyard nutrient requirements is essential for optimizing vine health, fruit quality and yield. Implementing soil testing and petiole analysis provides critical data to inform nutrient management strategies. A quality soil test or a previous year’s petiole analysis is important in understanding which nutrients the vineyard needs. 

Petiole analysis should be done at bloom and veraison, and at specific stages of vine development when nutrient concentrations in the petiole are most stable and representative of the vine's overall status. The most widely recommended timing for petiole sampling is at full bloom, which occurs when approximately 70% of the flowers on a cluster are open. This stage provides the most reliable data for key nutrients such as nitrogen, phosphorus, potassium and micronutrients. 

An alternative or complementary sampling period is at veraison, when about half of the berries on a cluster begin to change color or soften. Sampling at veraison can be useful for monitoring nutrients like potassium, magnesium and boron later in the season or for tracking changes in nutrient dynamics over time. 

Early hedging for healthier canopies and better ripening in cool climates

Early hedging, or cutting shoots shortly after they reach just above the top wire, can improve canopy efficiency and fruit ripening in cool-climate vineyards like those in northwest Michigan. Research from Michigan State University (MSU) shows that early hedging preserves younger, highly photosynthetically active leaves and promotes lateral growth, which supports ripening during late summer. It also reduces fruit zone shading and disease pressure while directing vine energy toward fruit development.

Timing is critical. Too early can cause overly dense canopies, especially in vigorous cultivars. When done correctly, early hedging improves canopy balance, fruit quality and ripening consistency in regions with short growing seasons.

Read more in the article “Early hedging for healthier canopies and better ripening in cool climates” from Michigan State University Extension.

Cluster zone leaf removal: Timing and technique 

To regulate grape quality in cool-climate regions, growers employ various canopy management practices to counter the challenges of a short growing season. One of the most impactful techniques iscluster zone leaf removal, which plays a key role in reducing disease pressure and enhancing fruit quality. 

This practice improves spray coverage and airflow around the fruit, lowering humidity and minimizing the risk of harvest season cluster rot complex, includingBotrytisand sour rot. Increased sunlight exposure also encourages development of a thicker wax cuticle on the berry skin, providing natural resistance to fungal infections and enhancing grape quality. 

Leaf removal can be performed manually or mechanically, and the industry is rapidly transitioning toward mechanization to improve both efficiency and economic sustainability. The effectiveness of this practice depends heavily on timing, particularly in relation to grapevine phenology. 

Leaf removal is typically applied between fruit set and veraison to improve cluster zone microclimate and increase disease resistance. When implemented around bloom or shortly before, it can also reduce fruit set and result in looser clusters, a valuable outcome for tight-clustered cultivars like Pinot noir and Riesling, which are prone to rot due to berry compression. 

Early leaf removal, at pre-bloom or pea-size stage, offers additional benefits under climate change conditions: 

  • Promotes flavonol synthesis, protecting berries from UV damage. 
  • Reduces incidence of cluster rot, potentially lowering fungicide use. 

Mechanical early leaf removal systems (Collard leaf remover) usecompressed airto remove leaves and dead flower tissue from the fruit zone. Removing dead ovaries is critical, as they serve as an entry point and nutrient base forBotrytisspores. The pathogen can remain latent until berry sugar levels rise and acidity drops, after which rot symptoms develop rapidly in warm, humid conditions. 

Read more in the MSU Extension article, “Cutting to the core: Michigan State research leads a canopy innovation in cool-climate viticulture.” 

Diseases 

In southwest Michigan, disease management of downy mildew, powdery mildew and botrytis fruit rot are the primary focus. The morning dews we will begin to experience are an important reminder to maintain protection against downy mildew. With tight clustered varieties, this is the last chance to get botrytis bunch rot sprays into the tight crevices of the clusters.

In northwest Michigan, disease pressure is still low but continues to increase in specific areas where black rot is becoming more apparent. Black rot symptoms are beginning to show up throughout the state (Photo 4), but it is largely too late to control these infections and fruits will begin to become resistant.

In this growing stage, consider choosing fungicides that control all the foliar and fruit diseases. For example, with downy mildew we are most concerned with foliar infection, and sprays should be timed regularly throughout the season when we experience heavy dews 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.

Black rot on grapes growing on a vine.
Photo 4. Black rot observed at the Trevor Nichols Research Center on July 16, 2025. Photo by Randy Smith.

If powdery mildew is the only concern, there are a number of effective products (FRAC codes 3, 7, 11, 13, U8, 50, and U13 as well as sulfur). Combining fungicides from different FRAC classes should also be effective while helping with resistance management.

Yellow spots on a grape leaf, a symptom of downy mildew infection.
Photo 5. Downy mildew on Niagara grapes at the Trevor Nichols Research Center on July 16, 2025. Photo by Randy Smith.

As we approach bunch closure in southwest Michigan, consider botrytis management. Several strategies contribute to good botrytis bunch rot management including opening up the canopy, properly applying fungicides, and using resistant cultivars when possible. Good botrytis control depends on getting good coverage. Just before bunch closure is the last chance to apply a fungicide to the inner part of the developing cluster. Fungicide resistance management is also important. The most effective products for botrytis are site specific and prone to resistance development. A Michigan Grape Fact Sheet is available for managing botrytis bunch rot.

As you choose a fungicide, check the guide for potential phytotoxicity of certain sprays on Concord grapes especially (this has been particularly noted for fungicides like Revus Top). Phytotoxicity risk is higher with high temperatures and quickly growing vines. Also, there is a significant phytotoxicity risk with specific contact products such as copper and sulfur for Labrusca type grapes (Concord and Niagara).

Insects  

In southwest Michigan, grape berry moth second generation continues to develop. Moth catches in traps have fallen to low levels over the past week, indicating the flight is close to being over in this region. This may also reflect growers applying insecticides to protect clusters from second generation larvae. For many sites in the southwest, the timing is approaching for two weeks following treatments applied at 810 or 910 degree days in early July. This treatment just before bunch closure is also important for getting coverage inside clusters where it can be challenging to reach with sprays once we are in August.

In northwest Michigan, the timing for protecting clusters against grape berry moth is coming this week (see table below), reflecting the much later phenology in northern Michigan this summer.

Farms in Berrien and Van Buren counties had mostly second and third stage grape berry moth larvae in clusters. We expect the ones that have survived to start pupation next week. The third generation is expected to start in early August in this area, and we will be using the Enviroweather degree day model to guide the timings for those applications. Many of the berries we observed with grape berry moth larvae had split following recent rains, and are likely to dry and fall off the vines before harvest (Photo 6).

Photo 6_Grape Report 071625.jpg
Photo 6. Grapy berry moth larva in a split open grape.

Treatment for grape berry moth at this time of the season can overlap with the need for protection against Japanese beetle, foliar phylloxera and leafhoppers, all insects that have been observed during scouting in southwest Michigan. Please check your own vineyards to determine the pest complex present at the sites. The MSU Fruit Pest Management Guide(bulletin E154) has recommendations of efficacy against key insect pests. A hard copy or a PDF version can be ordered from shop.msu.edu.

Japanese beetle on grapes.
Photo 7. Japanese beetles are becoming more active in northwest Michigan. Photo by Esmaeil Nasrollahiazar, MSU Extension.

Location 

Wild grape bloom biofix 

Predicted start of Gen 2 egglaying (810 GDD) 

Predicted start 
of Gen 2 egg hatch (910 GDD) 

Berrien Springs (Berrien Co.) 

June 2 

July 3 

July 6 

Lawton (Van Buren Co.) 

June 3 

July 4 

July 7 

Fennville (Allegan) 

June 4 

July 5 

Later than July 8 

Deerfield (Lenawee) 

May 28 

July 1 

July 5 

Romeo (Macomb Co.) 

May 30 

July 4 

Later than July 8 

NW Station (Leelanau) 

June 10 

Later than July 8 

Later than July 8 

SAM Tool 

TheSustainable Agricultural Management (SAM) Tool 's scouting function has been upgraded to better support scouting needs. Users can now upload photos up to 16 MB in size, a major increase from the previous 2 MB limit. This update significantly reduces the likelihood of encountering frustrating “file too large” errors—especially helpful when using newer smartphones that produce high-quality images.

While the file size of a photo depends on resolution, compression and content, most everyday smartphone cameras capture photos in the 12-16 megapixel (MP) range. These typically result in JPG files between 4-6 MB—well below the new 16 MB limit. Even 24 MP photos may now fit within the updated limit.

To illustrate the difference: The composite image below shows how much visual clarity is retained even when a 12 MP photo is resized down to 2 MP and 0.5 MP. At typical scouting scales, differences may appear minimal to the naked eye. However, when scouting for insects, diseases, or subtle damage, full-resolution images (12 MP or higher) may be valuable for accurate records or future diagnosis.

A composite image of grapes shown at 12MP, 2MP and 0.5MP file sizes.

In rare cases, some smartphones may capture photos larger than 24 MP. If this causes upload issues, resizing the image or adjusting camera settings (e.g., to “medium” photo quality) should resolve the upload problem.

For new users: Explore more functions at the web app and download the mobile app 

In addition to scouting, the SAM Tool helps manage vineyard activities such as assigning tasks, tracking restricted-entry intervals, maintaining farm calendars, and keeping searchable records.

Once workers or collaborators have signed up, farm managers can add them to the digital workforce using the “Add User” feature on the SAM Tool website. If you have suggestions or would like help getting started, please contact us atsustainableag@msu.eduor reach out to Karen Chou, PhD, directly atchouk@msu.edu. We’d be happy to show you how SAM Tool can support your vineyard’s recordkeeping, compliance and research efforts. 

Need help or have ideas for improvement?

We’re here to help—and we also need your help. The SAM Tool is being developed through the shared knowledge, feedback and dedication of many growers and MSU researchers. Your input is essential to shaping a tool that truly serves the needs of Michigan vineyards. If you have questions, want help getting started, or have suggestions for improvement, please contact us at sustainableag@msu.edu or reach out to Karen Chou directly at chouk@msu.edu. Let’s keep building the SAM Tool together!

Party on the Piazza: Volunteers needed plus Georgian wine tasting

For decorative purposes.

Join us for an evening of community, connection and celebration at Party on the Piazza on Thursday, Aug. 21, from 5-9:30 p.m. at the Grand Traverse Commons.

This relaxed, festive gathering brings together friends and colleagues from across Michigan’s wine and grape industry. One of the evening’s highlights will be a Georgian wine tasting led by Nino Sachaleli, PhD, a visiting expert from the Republic of Georgia. She’ll be sharing wines and stories from one of the world’s oldest winemaking traditions.

We’re also looking for volunteers to help make this event a success, whether it's setting up, pouring wine or helping with coordination. If you're interested in being part of the team, fill out the volunteer registration form by July 30.

You're also invited to bring a bottle of your own wine to share. Let’s make this a memorable celebration of wine, culture and connection. Raise a glass and celebrate the season together!

Michigan wines featured nationally at American Society for Enology and Viticulture Eastern Section wine tasting

For decorative purposes.

Thank you to the following wineries for their generous wine contributions to the American Society for Enology and Viticulture Eastern Section Wine Tasting. Their support was instrumental in highlighting the diversity and quality of Michigan wines on a national stage:

  • Brengman Family Wines
  • Chateau Chantal Winery
  • Filkins Vineyards
  • Mari Vineyards
  • Walloon Lake Winery

Thanks to their support, wines from all of Michigan’s major grape-growing regions—northwest, southwest, and the Tip of the Mitt—were proudly represented. The tasting highlighted the diversity and quality of Michigan wines to a national audience of growers, researchers, and wine enthusiasts.

Attendees responded with enthusiasm and curiosity, reinforcing Michigan’s growing reputation in cool-climate viticulture. MSU Extension also appreciates the many wineries and growers who offered to contribute. While time and logistics limited full participation, their support is valued.

These efforts are helping raise Michigan’s profile as a producer of world-class wines.

Upcoming events 

Third Thursday – Gibberellic Acid Vineyard Trial 

Join us for an on-site vineyard presentation and tour focused on the ProGibb trial. We’ll explore the use of Gibberellic Acid in Pinot Blanc and Riesling, testing its efficacy alone and with two surfactants (Embrece-EA and Talavera) to reduce cluster compaction and mitigate Botrytis risk. 

Date:Thursday, July 17, 2025 
Time:3:00 PM – 5:30 PM 
Location:Hawthorne Vineyards, 1000 Camino Maria Dr, Traverse City, MI 

Register 

The 36th annual Michigan Viticulture Field Day and 2nd annual Michigan Enology Experience 

Michigan State University’s famous Viticulture Field Day on July 30 is a staple for the state’s grape growing community. The latest local viticulture research will be showcased. New last year for the winemakers, MSU partnered with Lake Michigan College to add a second day for wine making education. The Michigan Enology Experience on July 31 provides hands-on education for new and established enologists alike.View more information and registration details. 

Register 

2025 Dirt to Glass Conference: Elevating Michigan Wine from the Ground Up 

Join grape growers, winemakers, researchers and industry leaders Aug. 21-22 in Traverse City, Michigan, for two days of insight, collaboration and innovation. From site selection to sustainable practices and wine marketing, this event is designed to strengthen Michigan’s wine industry—one vine and one voice at a time.Register nowand be part of the movement from intention to impact. 

Register 

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