MSU Extension Grapes

Key takeaways

• Southwest Michigan is advancing fastest, with growing degree days (GDDs) increasing from 472 to a forecasted 556.6 base 50 degrees Fahrenheit. Southern vineyards are generally at early shoot growth, cluster separation and inflorescence development, while northern regions remain mostly at bud swell, bud push or early bud break.
• Monitor for frost risk closely in northern vineyards, especially in the Tip of the Mitt region where cooler nights may approach frost or freeze conditions.
• Nutrient and canopy management should follow vine development. Southern vineyards may begin split nitrogen applications and prepare for shoot thinning within the next one to two weeks, while northern vineyards should delay nitrogen and canopy work until active growth is established.
• Bloom is the key disease-control window for black rot, powdery mildew and downy mildew. Scout carefully, protect open flowers and rotate fungicide FRAC groups.
• Grape berry moth activity is high in southern Michigan, but egg laying is not expected yet. Record Vitis riparia wild grape bloom to support grape berry moth model timing later in the season.
• Early-season pest and weed scouting is important. Flea beetle injury is generally tolerable, while tumid gallmaker should be monitored. Weed control should be based on weed presence, vine age, soil type and label restrictions.
• Soil health and recordkeeping remain priorities. Cover crops, compost, reduced compaction and tools such as the SAM Tool can support vineyard efficiency and long-term productivity.
• Upcoming industry events include P45 Third Thursday sessions, Michigan Viticulture Field Day and Enology Experience, and the 2026 Dirt to Glass Conference in Traverse City on Aug. 20–21.

Regional weather and seasonal progress

Seven-day forecasts for Michigan grape regions are as follows:

• Southwest Michigan: Benton Harbor, Fennville, Lawton, Watervliet
• Northwest Michigan: Old Mission, Suttons Bay, Traverse City, Leland, Northport
• Tip of the Mitt AVA: Petoskey, Harbor Springs, Charlevoix, East Jordan

Weekly in-season weather updates are provided to the MSU Extension fruit team by Jeff Andresen, PhD, MSU agricultural meteorologist. These reports offer timely insights into weather conditions affecting fruit production across Michigan. You can watch recordings of these agricultural weather outlooks.

Growing degree day (GDD) report

You can track vine development using the MSU Enviroweather Growing Degree Day Map. Visit the Enviroweather site to find your nearest weather station, create a free account, and monitor GDDs daily.

Biweekly GDD summary (base 50 degrees Fahrenheit)

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

Vine development

Southwest and southeast Michigan

In locations not damaged by the spring frosts and freezes, juice grapes and early hybrid wine grapes are currently at approximately 3–6 inches of shoot growth, with clusters separating and beginning to elongate. Hybrid and vinifera cultivars are generally between first leaf and about 1 inch of shoot growth.

In southeast Michigan, all cultivars are at the shoot elongation stage with inflorescence development. Wild grapes are also at the inflorescence elongation stage.

Northwest Michigan

Most Vitis vinifera cultivars have advanced beyond full dormancy and are currently pushing bud growth, with the first signs of green tissue visible. In some areas of the Leelanau Peninsula, early cultivars such as Cab Franc are now at bud break. Other cultivars remain in the bud swell stage, but development is expected to move quickly from this point forward if favorable weather continues.

Because development can vary considerably by location, cultivar, and microclimate, some vineyards may be slightly ahead of what was observed during scouting. Continue monitoring over the next several days as conditions change and vines continue to progress toward bud break.

Tip of the Mitt

In the Tip of the Mitt region, hybrid cultivars are at bud push. Vitis vinifera is beginning to push buds at the shoot apices. Closely monitor over the next several days as two cooler nights in the forecast may approach frost or freeze conditions.

For reference, see MSU Extension’s grape growth stages chart.

Viticulture

Early-season nutrient management should be guided by recent soil test results and prior-year petiole analyses. These tools provide essential information on nutrient availability and help inform fertilizer decisions as vines transition from dormancy to active growth.

In southern Michigan, where vines have reached early shoot development, nitrogen applications may begin using split applications to support growth while avoiding excessive vigor. Consider micronutrients such as zinc and boron to support early shoot and reproductive development. Monitor potassium and magnesium levels in vineyards with known deficiencies.

In northern regions, nitrogen applications should be delayed until active growth is established. This period is well suited for reviewing soil test results, finalizing fertility programs, and preparing for timely nutrient applications.

Nitrogen management remains critical across all regions. Excessive nitrogen can result in overly vigorous growth, delayed phenology and reduced fruit quality, while insufficient nitrogen may limit vine growth and yield potential. Balanced applications, guided by analytical data, are essential.

Canopy and crop management

In southern vineyards, shoot thinning is expected to begin within the next one to two weeks, depending on site and cultivar. Early canopy management decisions, including shoot thinning and initial crop load adjustments, should be based on vine vigor and uniformity. In northern regions, these practices will follow as vine development progresses and should be planned accordingly.

Soil health

Maintaining soil health remains an important component of vineyard management. Practices such as cover cropping, maintaining organic matter and minimizing soil compaction contribute to improved soil structure, water availability and nutrient uptake throughout the growing season.

For more detailed guidance on shoot thinning and early-season vineyard practices, please refer to the article “Early season vineyard management.”

Pest management

Diseases

Bloom is the most critical period for fruit infection from black rot, powdery mildew and downy mildew. Scout carefully and protect open flowers with fungicides during this period.

Fungicide programs at bloom should prioritize materials with strong protectant and systemic activity, while rotating modes of action to manage resistance. Products in FRAC groups 3 (DMIs) and 11 (QoIs), often used in premixes, remain key options for powdery mildew and black rot, while multi-site protectants such as captan (M4) or mancozeb (M3) provide additional coverage and help reduce resistance risk.

For downy mildew, materials in FRAC groups 40, 45, 21 and 11, as well as phosphorous acid products, are effective choices when conditions favor infection. Careful selection and rotation of these chemistries, combined with thorough coverage during bloom, are essential to protect developing clusters and limit early-season disease establishment.

Insect pests

Grape berry moth traps indicated high activity of male moths across southern Michigan in the recent warmer weather. This first period of activity is not associated with egglaying by females, but we will continue to monitor a few sites to check on young clusters.

The next step for grape berry moth integrated pest management is to identify the timing of wild grape bloom. Track this and record the date for your vineyard site(s) so you have that later for the grape berry moth model timings in July and August.  The date to record is when 50% of the flowers are open on 50% of wild grape clusters. Make sure you have the correct wild grape species. This is Vitis riparia, which has glossy undersides to the leaves and blooms before Concord. The other common wild grape, Vitis aestivalis, should not be used because it blooms after Concord with short, whitish-gray hairs on the leaf underside and red tendrils.

As new leaves expand, “window-pane” damage is visible on leaves where flea beetle activity was observed last month. Vines can withstand this leaf damage and it rarely reaches economic injury levels.

Grape tumid gallmaker symptoms were observed on hybrid grapes this week. This can be isolated to a few vines where infested leaves and clusters can be removed and destroyed. Widespread infestation may require treatment to protect leaves and clusters. Assail is one effective option that can protect from further infestation.

Weeds

Early-season weed management is important in vineyards to reduce competition for water, nutrients and light, especially in young or newly planted blocks. Maintaining a relatively clean undervine strip during early shoot growth can support vine establishment, improve nutrient uptake and reduce competition during a critical period of vine development.

Scout vineyard floors now to identify winter annuals, emerged summer annuals and perennial weeds. Winter annual weeds may already be flowering or setting seed, so timely control can help reduce seedbank inputs. Summer annual weeds such as pigweed, lambsquarters, foxtails and annual grasses will continue emerging as soils warm.

Several herbicide options are listed in the 2026 Michigan Fruit Management Guide. In established vineyards, the first step is to determine whether weeds have already emerged.

If the vineyard floor is clean, a residual herbicide such as Chateau, Prowl H2O, Surflan, Princep, Karmex, Zeus XC, Zeus Prime XC or Alion may be used, depending on vine age, soil type and label restrictions.

If weeds are already present, include a labeled burndown herbicide such as glufosinate, paraquat, glyphosate, Aim or Venue with the residual product. Examples include glufosinate + Chateau, glyphosate + Prowl H2O, glufosinate + Zeus XC or Zeus Prime XC, glyphosate + Princep, or Karmex + Prowl H2O or Surflan, where labeled and appropriate. Apply Zeus XC and Zeus Prime XC to weed-free soil or with a burndown partner if weeds are present. They should not be tank-mixed with Chateau.

For grass-only problems, Fusilade DX, Poast or Assure II may be used when grasses are actively growing. Organic growers may consider caprylic plus capric acid products where labeled.

Apply all postemergence herbicides as directed sprays to the vineyard floor and avoid contact with green shoots, leaves, green bark, suckers, and young vines. Always follow the label for crop age restrictions, rates, adjuvants, preharvest intervals, and tank-mix compatibility. Rotate herbicide sites of action and integrate mowing, cultivation, cover crops, or other nonchemical tactics to reduce herbicide-resistance risk.

Scouting and recordkeeping tools

The growing season is an ideal time to implement efficient scouting, spray planning and recordkeeping systems. The Sustainable Agriculture Management (SAM) Tool, developed for Michigan grape growers, provides a user-friendly platform to support spray and non-spray task management.

Recent updates have improved functionality, including streamlined task planning, easier editing and duplication, improved activity tracking and enhanced communication features. The tool also offers a redesigned mobile interface and supports grower-participatory research.

The SAM Tool is free to use and suitable for vineyards of all sizes. Growers are encouraged to incorporate it into their operations to improve efficiency, organization and decision-making throughout the season.

Personalized onboarding and support are available through the SAM Tool team. For assistance or to schedule a walkthrough, visit the SAM Tool website or contact the team directly at SustainableAg@anr.msu.edu.

Events and announcements

We are pleased to share the upcoming schedule for this season’s P45 Third Thursday events. These sessions are designed to provide timely, field-based insights and practical demonstrations aligned with current vineyard conditions. More details will be shared as the season progresses. We encourage growers and industry members to mark their calendars and plan to attend.

June 18 – Mawby Vineyard | Compost Tea

Join us at Mawby Vineyard for a discussion on compost tea applications and their role in soil health and vineyard management. This session will focus on practical considerations, potential benefits and integration into existing vineyard programs.

July 16 – Northwest Michigan Horticulture Research Center | Sap Analysis

This session will highlight using sap analysis as an in-season tool for monitoring vine nutrient status. Discussion will include interpretation of results and how to incorporate sap data into nutrient management decisions during the growing season.

August 6 – Northwest Michigan Horticulture Research Center | Spray Efficacy Workshop

This workshop will focus on improving spray efficacy in vineyard systems. Timothy Miles, PhD, and Mike Reinke, PhD, will lead discussions on optimizing spray programs, coverage and disease control. The session will also feature demonstrations of drone-based sprayers and newly available autonomous spray technologies. Additional expertise from an invited out-of-state speaker is anticipated.

37th annual Michigan Viticulture Field Day and Enology Experience

Registration is opening soon for the 2026 Michigan Viticulture Field Day and Enology Experience.

The Michigan Viticulture Field Day program will highlight new technologies for grape growers with demonstrations of autonomous and smart spraying systems and electric weeders. Sustainable viticulture practices will also be showcased, such as non-chemical weed management strategies, sheep grazing and the new MSU regenerative and organic demonstration vineyards.

The Michigan Enology Experience will include discussions on innovative winemaking technology, a hands-on tasting workshop and guided tastings of experimental wines from Lake Michigan Vintners and other wineries from southwest Michigan. The day will conclude with a blind comparative wine tasting pitting Lake Michigan Shore wines against international standards.

2026 Dirt to Glass Conference

Registration is open for the fifth annual Dirt to Glass Conference, taking place Aug. 20–21 in Traverse City, Michigan. Early bird pricing is available for a limited number of registrations.

Register for the 2026 Dirt to Glass Conference

The program features 23 speakers covering vineyard management, winemaking, soil science, vine physiology and wine evaluation, combining Michigan expertise with national and international perspectives. The conference is designed as a working forum with moderated panel discussions focused on practical, vineyard-to-winery decision-making.

Highlighted speakers include:

• Nick Dokoozlian (E. and J. Gallo) – vineyard-to-wine quality benchmarks
• Jacopo Miolo (Simonit and Sirch) – pruning and vine longevity
• Tom Plocher – disease-resistant varieties
• Madeline Triffon – sensory evaluation
• Bruno Basso (MSU) – soil health and site-specific management

The program also features applied sessions on scouting, soil biology and vineyard establishment.

A key focus this year includes collaboration with E. and J. Gallo to pair sensory evaluation of Michigan wines with advanced chemical analysis, supporting improved quality assessment and production strategies.

The conference includes a two-day format:

• Day one (Aug. 20): technical sessions, panel discussions and guided tastings at the Cathedral Barn at Historic Barns Park
• Day two (Aug. 21): field tours of vineyards and wineries with visiting experts

Space is limited. Day two participation requires day one registration.

This work is supported by the Crop Protection and Pest Management Program [grant no 2024-70006-43569] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.