MSU Extension Grapes

Key takeaways

• Vine development varies by region. Southwest Michigan grapes range from pea-size berries to bunch closure, northwest Michigan Vitis vinifera berries are about 7–9 millimeters and remain firm and green, and some early cultivars in southeast Michigan are beginning veraison.
• Disease pressure is increasing. Downy mildew is spreading in some southwest Michigan vineyards while downy mildew, powdery mildew and black rot remain concerns in northern regions. Maintain protective fungicide coverage and rotate FRAC groups to reduce risk of resistance.
• Canopy management should match vine vigor. Continue east-side leaf removal where appropriate, monitor canopy density and avoid hedging too early in vigorous vineyards, which may encourage excessive lateral growth.
• Japanese beetles and grape berry moth remain important insect concerns. Scout foliage and clusters, especially in historically high-pressure sites, as second-generation grape berry moth activity continues in southwest Michigan.
• Manage soil moisture and competition. Mow cover crops as needed, avoid unnecessary late nitrogen applications and limit equipment traffic on wet soils to reduce compaction and protect root function.
• Scout summer weeds before they become large or drought stressed. Match herbicides to the weed species present, use directed applications and prevent contact with grape leaves, shoots, green bark and young vines.
• Use weather and growing degree day (GDD) tools to guide management. Michigan State University (MSU) Enviroweather forecasts and growing degree-day maps can help growers track vine development, pest timing and regional differences.
• Several educational events are approaching. Upcoming programs include the Aug. 6 Spray Efficacy Workshop and the Aug. 20–21 Dirt to Glass Conference in Traverse City.

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 southwest Michigan, juice grapes and early hybrid cultivars continue to be near berry touch, while some tight-clustered varieties are beginning bunch closure. Many Vitis vinifera cultivars are near pea-size berry stage. Downy mildew is starting to spread quickly starting last week. Many varieties are getting past susceptibility to black rot. Leaf pulling on east sides of vines has been progressing for a couple weeks. Some growers are beginning to hedge in vigorous locations, but many are holding off as long as possible to reduce side shoot growth.

In southeast Michigan, the first clusters of Marquette are at veraison. Japanese beetles continue to cause damage to foliage. Monitor for spotted lanternfly, which has been found in the region.

Northwest Michigan

Across northwest Michigan, grape berries are about 7–9 millimeters in diameter, ranging from peppercorn size to pea size. The berries remain firm and green. In tighter clusters, they are beginning to touch as the clusters continue to fill out.

Tip of the Mitt

Hybrid cultivars are beginning bunch closure and beginning to soften. Vitis vinifera cultivars are approaching the berry touch stage. Japanese beetle activity is persistent. Black rot, downy mildew and powdery mildew have been noted in some vineyards. Risk for each remains moderate.

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

Viticulture

Maintaining a well-balanced canopy and healthy vineyard soils is essential for sustainable vine growth, high-quality fruit, and effective disease management. The following section highlights important early- and mid-season viticulture practices that can improve canopy function and support fruit ripening.

Early hedging

Early hedging involves trimming shoots shortly after they grow beyond the top catch wire. This practice helps redirect vine resources from continued shoot growth toward fruit development.

Research from Michigan State University suggests that properly timed early hedging can retain young, highly photosynthetically active leaves and encourage moderate lateral shoot growth. These leaves can contribute to sugar accumulation and fruit ripening later in the season.

Timing is important. Hedging too early may stimulate excessive lateral growth and create a dense canopy, particularly in vigorous cultivars or vineyards with high soil fertility. Growers should consider vine vigor, cultivar, and canopy density before deciding when to hedge.

Recommended reading from MSU Extension:

• Early hedging for healthier canopies and better ripening in cool climates
• Cutting to the core: Michigan State research leads a canopy innovation in cool-climate viticulture

Soil health

During berry development, healthy soils help maintain steady vine growth, nutrient uptake and fruit development.

• Manage cover crops: Mow row middles as needed to control excessive growth and reduce competition with vines for water and nutrients. This is especially important during hot, dry periods or in younger vineyards with less-developed root systems.
• Maintain soil moisture: Monitor soil moisture and avoid both prolonged drought stress and saturated conditions. Consistent moisture supports continued berry growth, nutrient uptake and overall vine function.
• Limit late nitrogen: Avoid unnecessary nitrogen applications at this stage. Excess nitrogen can stimulate unwanted shoot and lateral growth, increase canopy density and delay fruit ripening.
• Prevent compaction: Minimize tractor and sprayer traffic when soils are wet. Compacted soils have reduced drainage and aeration, which can limit root growth and nutrient uptake.

Recommended MSU resources:

• Rooting the future: The untapped power of cover crops in Michigan vineyards
• Building climate resilience in vineyards: Carbon sequestration as a tool for sustainable winegrowing

Pest management

Diseases

Fungicide programs 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

Japanese beetles and grape berry moth are the main insect pests to focus on in mid-July. They are highly variable across sites, with some typically affected berry moth vineyards showing low infestation levels. This could be from effective treatments, the stress of extreme heat on berry moth populations, or both.

The grape berry moth model on MSU Enviroweather has reached the predicted timing for continued activity of the second generation in Southwest Michigan. Growers that typically get infestations should do some cluster scouting during the next few weeks to see if there’s continued activity of berry moth that needs control in August. 

Weeds

Summer weed management in vineyards should focus on scouting and controlling weeds that escaped spring preemergence herbicide programs or emerged after residual activity began to decline. This is especially important during hot, dry periods because weeds compete with vines for soil moisture and nutrients at a time when vines may already be under heat and water stress. Young or newly planted vineyards are especially vulnerable, but even established vineyards can lose vine vigor when large weeds are allowed to remain in the undervine strip.

Growers should scout vineyard floors now and identify which weeds are present, their size, and whether they are broadleaves, grasses or perennial weeds. Summer annual weeds such as pigweed, lambsquarters, ragweed, foxtails, crabgrass, barnyardgrass and other annual grasses may continue to emerge through the summer, especially after rainfall or irrigation. Perennial weeds such as Canada thistle, bindweed, quackgrass, yellow nutsedge and dandelion may also be present and often require repeated management. If spring residual herbicides were applied earlier in the season, some breakthrough is expected as those products begin to lose activity, especially where weed pressure is high or where rainfall patterns affected activation or persistence.

Postemergence herbicides are most effective when weeds are small and actively growing. During heat waves or droughty periods, weeds may be stressed, dusty, hardened off or less actively growing, which can reduce herbicide performance. If possible, target applications before weeds become large and avoid waiting until weeds are moisture-stressed. Good spray coverage is especially important for contact herbicides. Also consider vine stress: avoid drift, use directed sprays, and do not allow herbicides to contact grape leaves, green shoots, green bark, suckers or young vines.

Several postemergence options are listed in the 2026 Michigan Fruit Management Guide for grapes. In established vineyards, glufosinate can be used as a directed application to actively growing weeds and is generally more effective on smaller weeds; higher labeled rates may be needed for larger weeds. Paraquat provides contact control of emerged annual weeds, but coverage is critical and it must be kept off green grape tissue. Aim can be used for burndown of small broadleaf weeds and is often most useful when weeds are small. Venue can be tank-mixed with glyphosate or glufosinate to improve desiccation of small broadleaf weeds. Gamma may also be used in grapes established at least two years and should be applied with another postemergence herbicide to improve control of established weeds. Glyphosate can control annual and perennial weeds, but it must be used with caution in grapes because contact with leaves or green shoots can cause serious injury, and applications after bloom should generally be avoided based on label and guide precautions.

For grass-only problems, products such as Fusilade DX, Poast, or Assure II may be used when grasses are actively growing and within the labeled size range. These products will not control broadleaf weeds, so growers should match the herbicide to the weed spectrum present. For mixed broadleaf and grass populations, a broader postemergence program or tank mix may be needed where labeled and appropriate.

At this point in the season, adding another residual herbicide may only be useful if the label allows the timing and if rainfall or irrigation is expected to activate the product. In established vineyards, some residual options such as Prowl H2O may be applied during the growing season where labeled, but residual herbicides will not control large emerged weeds by themselves. If emerged weeds are present, a labeled burndown partner is needed.

Always follow the product label for grape age restrictions, rates, adjuvants, maximum seasonal use, preharvest intervals, restricted-entry intervals, tank-mix compatibility and crop-safety precautions. Apply all postemergence herbicides as directed sprays to the vineyard floor and avoid contact with green grape tissue. Rotate herbicide sites of action and integrate mowing, cultivation, cover crops or other nonchemical tactics where possible to reduce herbicide-resistance risk and improve long-term vineyard floor management.

Scouting and recordkeeping tools

The Sustainable Agriculture Management (SAM) Tool continues to evolve through close collaboration with Michigan vineyard managers. By observing day-to-day vineyard operations and listening to grower feedback, the SAM Tool team is identifying opportunities to reduce bottlenecks in task management, communication, and recordkeeping. Recent vineyard visits have revealed several management challenges, and solutions to these pain points will be incorporated into upcoming SAM Tool releases.

What's New in the SAM Tool? One exciting direction for the SAM Tool is expanding its role in supporting grower–researcher collaboration. In addition to helping manage vineyard operations, the platform is being enhanced to facilitate participatory research, allowing growers to contribute valuable field observations while helping MSU researchers develop practical solutions for the grape industry.

The first of these collaborative efforts is the Grape Yield Estimation Project, a partnership between Michigan grape growers and MSU researchers. Growers who participate will not only help evaluate new technologies for estimating grape yield and contribute to the development of future vineyard management tools, but will also help build a vineyard-specific database that will lay the foundation for future SAM Tool features designed to evaluate how vineyard management practices may influence yield over time.

If you are interested in participating in the Grape Yield Estimation Project or would like to learn more about the SAM Tool, please contact the SAM Tool team at sustainableag@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. 

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

Join us for a hands-on Spray Efficacy Workshop focused on emerging technologies for vineyard pest and disease management. Mike Reinke will discuss the benefits, limitations and practical considerations of precision and autonomous sprayer systems. The program will also include live demonstrations of a spray drone and an autonomous airblast sprayer, along with discussion of vineyard row spacing, equipment access and how these technologies may fit into commercial operations.

• In-person registration
• Zoom registration

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.