MSU Extension Grapes

Weather Update

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

• Southwest Michigan: Benton Harbor | Fennville | Lawton
• Southeast Michigan:  Romeo
• Northwest Michigan: Old Mission | Petoskey | Traverse City

Agricultural Weather Outlook

Weekly in-season weather updates are provided to the MSU Extension fruit team by Jeff Andresen, 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:

Weather forecast

The first week of June was seasonable for Michigan. Much of the state saw temperatures in the 70s with an occasional day up into the 80s. Low temperatures hovered near 50 degrees. Degree day development was average this time of year. 

A pair of storm systems crossed through Michigan on Wednesday of last week. One moved on a west to east track through the southern tier of counties, dropping up to an inch of rain in some locations. A second passed over the northwest portions of the lower peninsula in a northeastern track, leaving about two-thirds of an inch of rain. Some scattered rains on Sunday and Monday brought another tenth of an inch of rain. Weekly rain totals for much of the grape growing regions of Michigan were close to an inch.

This next week should see a continuation of the seasonal weather. Temperatures are expected to stay near 70 degrees in northern Michigan, upper 70s in southern areas. Models are indicating a chance for a weather system to stall over Michigan in the latter part of the week. The entire state is expected to see rain on Thursday through Saturday with the possibility of the system lingering later. No severe storms are expected, but up to an inch of rain is possible. 

Even with the rains last week, parts of Michigan are seeing dry soils. The rain amounts last week were enough to meet the water needs for grapes. At this time of year, the evapotranspiration models indicate plants want an inch to an inch and a quarter of water per week. Last weeks rains and this week’s forecast are enough to satisfy these needs, but not enough to recharge soils with surplus. Parts of Southern Michigan are still seeing abnormally dry soils: https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?MI. As we get to bloom, the vines will potentially need some additional water. For those that have irrigation installed, testing the systems ahead of the need can save emergency repairs later down the road. 

Vine growth

In southern Michigan, Juice grapes and early hybrids are in bloom. Clusters are separating in the remaining varieties. Shoot thinning is continuing for a third week. Wild grape bloom is widespread. Early wild grape bloom was seen near Memorial Day, but became more widespread after the warmup that started near the first of June. 

In northern Michigan, Vitis vinifera varieties are making steady progress, with shoots now measuring 5–11 inches and initial clusters becoming clearly visible.

Following last week’s mild weather, shoot growth continues at a healthy pace. This is an ideal time to prioritize canopy management activities such as shoot thinning, and nutrient scheduling. Tracking phenology at this stage enhances decision-making for pest management, fertilization, and canopy work. For detailed staging, refer to MSU Extension’s Grape Growth Stages chart.

Additionally, wild grapes are now in full bloom, which marks an important phenological milestone. This bloom is used as the “biofix” to calibrate MSU’s Enviroweather grape berry moth degree-day model—critical for predicting the timing of the first, second, and third moth generations.

In the Tip of the Mitt AVA, hybrid cultivars are in the 10-16 inch shoot stage with clusters clearly visible. Some hybrid cultivars in warmer areas of the AVA are in the immediate pre-bloom stage. Vitis vinifera cultivars are in the 4-8 inch growth stage. 

In Southeast Michigan, the very first blossoms have been seen in ‘Canadice’ in Britton. Hybrid wine grapes as well as table grapes in the region are still at the pre-bloom stage with continued shoot extension. Grape berry moths have been caught in traps at Kapnick’s and Youngblood’s. Powdery mildew risk is high this week, though fruit is not present for infection.

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 what nutrients the vineyard needs. Petiole analysis should be done at bloom and veraison. Petiole analysis should be conducted 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 percent 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. The accuracy of petiole analysis depends heavily on sampling the correct leaf position. At full bloom, the petiole should be collected from the leaf that is directly opposite the basal grape cluster, typically the fourth to sixth leaf from the base of the shoot. This leaf is considered physiologically mature and reflective of the vine’s nutrient reserves at bloom. At veraison, petioles should be collected from recently matured leaves, generally located around the fifth to seventh leaf from the shoot tip. A representative sample should include petioles from a sufficient number of vines across the block or variety, ideally 60 to 100 petioles collected from at least 20 to 25 randomly selected, healthy vines. Leaves chosen for sampling should be free of visible disease, pest damage, or physical injury. To avoid contamination, petioles should be collected with clean tools and placed in a paper bag (not plastic) to allow for air drying. Samples should be clearly labeled with block, variety, date, and phenological stage, and should be dried or delivered promptly to a testing laboratory.  Properly conducted, petiole analysis provides a clear snapshot of vine nutritional health and supports informed management decisions that contribute to balanced growth, fruit development, and overall vineyard sustainability.

Soil tests evaluate nutrient content, pH levels, and other soil characteristics, offering insights into the soil's fertility and potential nutrient deficiencies. Petiole analysis, which involves testing the leaf of grapevines, directly measures the nutrients absorbed by the plant, providing a more immediate understanding of the vine's nutritional status. Regular monitoring through these methods allows for timely adjustments to fertilization practices, ensuring optimal nutrient availability throughout the growing season. During the early stages of vine growth, particular attention should be given to the application of nitrogen (N), zinc (Zn), and boron (B), as these nutrients are vital for shoot development and flowering. Potassium (K) and magnesium (Mg) are also important during this period, supporting various physiological processes within the vine.

Nitrogen plays a crucial role in vegetative growth and fruit development. However, its application must be carefully managed:

• Excessive Nitrogen: Can lead to delayed flowering and excessive vegetative growth, potentially compromising fruit set and quality.
• Insufficient Nitrogen: May result in reduced vine vigor, leading to lower yields and diminished fruit quality.

Therefore, precise nitrogen management, informed by soil and petiole analyses, is essential to balance vegetative growth and fruit production effectively. Shoot thinning will begin in the southern vineyards in the next week or two. Shoot thinning is an important canopy management tool to improve air circulation, minimize disease pressure, reduce shading, and improve spray penetration. The right time for shoot thinning time is when the shoots are 5-12 inches long.

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

Diseases

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 pre-bloom fungicide options and the effects of rain on disease spread, I recommend referring to a grape scouting report from earlier 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.

Insects 

Continued thrips activity has been observed in vineyards in SW Michigan this week, with activity mostly on clusters that are in bloom. These are tiny insects that can best be sampled by tapping clusters over a phone screen or sheet of paper. We have also deployed yellow sticky boards, and some of those had high densities of thrips when checked this week. We don’t have thresholds developed for these pests, but their feeding in spring can lead to reduced fruit set and “giraffe skin” scarring on clusters at harvest time. 

Grape berry moth adult catches in traps are still high across southern Michigan sites where we are monitoring, but we are not yet finding GBM eggs or larvae in clusters. With bloom underway we expect first generation egglaying in the coming weeks. However, this early-season activity is usually very low and clusters can compensate for low levels of early season feeding. Getting a close read on the bloom timing of Vitis riparia (wild grape) is important for initiating the grape berry moth model that is posted on MSU’s Enviroweather system. Although there were some early sites with bloom in late May, there was widespread wild grape bloom in Berrien County around June 2. We should be checking the wild grape vines with a shiny underside which distinguishes them from summer grape.

Yellow sticky trap showing high thrips density at some vineyards where bloom is underway—highlighting the need for vigilant monitoring and control.

Potato leafhopper has been detected in SW Michigan, which was predicted given the recent weather systems with airflow from the southern sections of the Mississippi Valley. Growers of grapevines that are stunted by this pest are advised to scout their plants to check for leafhoppers, and should protect susceptible cultivars especially young vineyards where this pest can stunt shoot growth. Neonicotinoid insecticides such as Assail and Admire Pro can provide protection against potato leafhopper, rose chafer and tumid gallmaker if present in the same vineyard site.

SAM Tool New Mobile App for Vineyard Scouting & Recordkeeping

Whether you’ve used the SAM Tool before or are just getting started, this year’s updates are designed to make recordkeeping and task management easier and more efficient—right from your smartphone or desktop.

New Mobile App – Please Delete the Old One

If you have the older version of the SAM Tool mobile app on your phone, please delete it and download the new version to ensure full access to the updated features. Use the QR codes below to install the latest version:

• Download mobile app from the Google Play
• Download mobile app from the Apple Store

Roles and Access:

• Managers and workers can access their associated vineyards on both the desktop and mobile apps.
• Managers can create, edit, and perform tasks.
• Non-managerial workers can view and perform assigned tasks only.
• To add workers to your digital workforce:
1. Ask your workers to download the app and sign up using their email.
2. As a manager, use the "Add User" function and enter the worker's email to bring them into your team.
3. Once added, workers can use their phones to view and complete their assigned tasks.

Desktop or Mobile – Use What Works Best for You

While the mobile apps offer powerful on-the-go access, some users may still prefer the desktop version for creating and managing tasks. You can use both—the SAM Tool is designed to support your workflow in the field and in the office.

To learn more about the SAM Tool or to get started, visit https://sustainableag.msu.edu/ or contact Karen Chou at chouk@msu.edu. For this growing season, we are offering one-on-one assistance to help growers migrate their management plans into the SAM Tool.

Upcoming Events

Michigan Grape Society’s June Twilight grape growers social - June 18th

The June growers’ social will be at St. Julian’s Mountain Road vineyard. In addition to the great wine and pig roast, Paolo Sabbatini will be leading a discussion on canopy management. Activities begin at 6:00pm. Register here: https://michigangrapesociety.simpletix.com/

 You're Invited: Third Thursday – Biochar & Drone Demonstrations

• Thursday, June 19 | 1:00–4:30 PM
•  Shady Lane Cellars, Suttons Bay, MI
•  Hybrid Event (In-Person & Online Options)

Join us for our June Third Thursday event featuring two hands-on demonstrations:

Biochar Production & Vineyard Applications

Learn about biochar production and its potential to improve soil health and sustainability in vineyards.

Drone Spray Demonstration

Explore the latest in aerial spray technology and strategies to reduce chemical use in vineyard pest and disease management.

This informal, educational event is open to all and will include RUP credit opportunities (pending approval).

Stay tuned—we’ll be sharing more details and the registration link soon!

The 36th annual Michigan Viticulture Field Day and 2nd Michigan Enology Experience are approaching - July 30-31

Michigan State University’s famous Viticulture Field Day 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 provides hands-on education for new and established enologists alike. More information and registration can be found here: https://www.canr.msu.edu/news/2025-michigan-viticulture-field-day-and-michigan-enology-experience-july-30-31

Register for 2025 Dirt to Glass Conference – August 21–22, Traverse City

Join grape growers, winemakers, researchers, and industry leaders 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 now and be part of the movement from intention to impact.

MDARD Seeks Wine Grape Grower Input

Advisory committee nominations accepted through June 11, 2025

LANSING, Mich. – The Michigan Department of Agriculture and Rural Development (MDARD) is seeking input on the potential establishment of a legislatively enacted Michigan wine grape commodity group after growers submitted enough signatures to pursue organization. The department is currently taking nominations for a temporary advisory committee composed of industry members, which will oversee the process moving forward.

“MDARD is committed to maintaining a diverse food and agriculture industry within Michigan and highlighting unique agricultural opportunities,” said MDARD Director Tim Boring. “The potential establishment of a wine grape commodity group would support Michigan craft beverage producers and businesses to continue to grow their product, expand their knowledge and improve their economic impact.”

In Michigan, Public Act (P.A.) 232 provides an avenue for commodity growers to organize and vote on whether or not to establish a legislatively enacted commodity group. Two hundred signatures or 25 percent, whichever is lower, from growers are first needed to start the process, which are then submitted to MDARD as required by the statute. MDARD currently has legal, fiscal and program oversight responsibility for 15 legislatively established commodity boards.

Michigan wine grape growers, and businesses affiliated with the purchase of Michigan wine grapes, are encouraged to submit their contact information to receive updates about the P.A. 232 process, including information on committees, public hearings, and referendums.

Using this form, grape growers may also nominate themselves to participate in the temporary advisory committee. Survey responses are due June 11, 2025 to be considered for the committee.

The responsibilities of a temporary advisory committee will include developing program recommendations to be considered by fellow wine grape growers at future public hearings. If the feedback at those hearings is positive, a referendum date will be set for qualified producers of the commodity. A successful referendum is the final step in enacting a wine grape P.A. 232 group.

Media contact: Lynsey Mukomel, 517-290-1734

Related Articles: 

• Early season vineyard management
• Early season control of grape berry moth in Michigan vineyards for 2022
• Rose chafer management for northwest vineyards
• Fruit insecticide registration update for 2023 
• Southwest Michigan fruit update – June 4, 2024
• https://www.canr.msu.edu/news/michigan-grape-scouting-report-june-15-2022 
• 2022 MSU Fruit Pest Management Guide (E-154)
• Grape growth stages
• Early season vineyard disease management
• Early season vineyard management
• A Mobile Guide for Grape IPM Scouting in North Central and Eastern U.S.
• Using the MSU Enviroweather grape berry moth model in 2018