MSU Extension Grapes

Key takeaways

• Spotted lanternfly was detected in southern Berrien County, marking the first reported detection in southwest Michigan. The finding was in a park—not a vineyard—but growers should remain alert and scout regularly.
• Harvest is underway in southern Michigan, while many cultivars in northwest Michigan and the Tip of the Mitt continue through veraison and ripening. Cool conditions are slowing sugar accumulation in some locations.
• Monitor fruit maturity and condition closely by regularly measuring degrees Brix, pH and titratable acidity and checking clusters for sour rot, Botrytis, insect injury and bird damage.
• Late-season pest pressure remains important, including powdery and downy mildew, leafhoppers, vinegar flies, yellow jackets and grape berry moth. Follow preharvest intervals and coordinate late-season treatments with the winery.
• Bird protection should begin before significant feeding occurs. Netting remains the most reliable option, while visual and acoustic deterrents work best when combined and frequently repositioned.
• Pre-veraison leaf removal and cluster thinning can work together to improve fruit uniformity, color development, ripening and cluster health when matched to cultivar, vine vigor and production goals.

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

We are in the second week of harvest. Early hybrids like Marechal Foch, Itasca and Marquette have already been harvested. Early Pinot Gris is also being harvested for sparkling uses. The cool weather seems to be slowing sugar development. Sour rot is starting to show up as well. Isolated crop loss due to birds is showing up in advanced varieties.

In Southeast Michigan several early-ripening hybrid cultivars have already been harvested such as ‘Itasca’ and ‘Marquette.’ In table grapes growers have harvested ‘Marquis,’ ‘Venus,’ and ‘Vanessa’ and will be starting ‘Mars.’ In the warmer parts of the region close to the Ohio border ‘Concord’ as it first pick while further north growers are picking their first clusters of ‘Fredonia.’ Growers should also monitor for spotted lanternfly, which has been found in the region.

Southwest Michigan Research and Extension Center - September 10, 2026:

Northwest Michigan

Across northwest Michigan, wine grape cultivars continue to advance toward ripening, although progress remains variable among cultivars. At vineyards on the Old Mission Peninsula, Cabernet Franc and Merlot are approximately 50% through veraison, with noticeable color development. Earlier-ripening varieties have largely progressed beyond veraison and are approaching technological maturity, while later-ripening cultivars remain in the lag phase of berry development.

These differences in developmental timing highlight the asynchronous nature of ripening across grape varieties in the region. As fruit maturation accelerates over the coming weeks, close monitoring of soluble solids, acidity, pH, and overall fruit condition will be essential for optimizing harvest timing and fruit quality.

For a precise visual reference, consult MSU Extension’s Grape Growth Stages chart.

Northwest Michigan,  Old Mission TWP - September 9, 2026:

Tip of the Mitt

Vitis vinifera and hybrid cultivars are progressing through veraison nicely with early hybrid cultivars such as Itasca and Osceola Muscat nearing harvest in the Southern areas of the Tip of the Mitt. Japanese beetle activity is still persistent. 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.

Northern Michigan, Tip of the Mitt - September 9, 2026:

Viticulture

Two vineyard management practices, pre-veraison leaf removal and cluster thinning, are widely used in Michigan vineyards to improve grape and wine quality, particularly in premium wine production. Each practice can provide benefits on its own, but research from the Michigan State University Department of Horticulture has shown that, when properly timed and combined, they can further improve fruit composition, disease management and overall vine balance.

The combined effect

When pre-veraison leaf removal and cluster thinning are used together, their effects can be complementary. Cool-climate studies with ‘Cabernet Franc’ at the Southwest Michigan Research and Extension Center found that the combined treatment improved fruit uniformity, increased anthocyanin accumulation and advanced ripening more effectively than either practice alone.

In warmer climates, treatment differences may become less pronounced by harvest, although earlier improvements in ripening and cluster health can still be valuable, particularly under high disease pressure. These vineyard responses can also carry through to wine quality, with combined canopy and crop-load management associated with improved color, aromatic intensity and structural characteristics.

The key is to use both practices strategically rather than routinely. Their effectiveness depends on cultivar, vine vigor, crop level, canopy density, seasonal conditions and the desired production goals. Read more information on cluster thinning.

Preparing for harvest

As harvest approaches, vineyard management should shift toward close monitoring of fruit maturity and preservation of fruit quality. Representative berry sampling should be conducted regularly to track soluble solids (Brix), pH and titratable acidity, while also considering berry flavor, seed maturity, cultivar characteristics and the intended wine style when determining harvest timing. At the same time, clusters should be monitored carefully for Botrytis bunch rot, sour rot, insect injury and increasing bird pressure, all of which can accelerate fruit deterioration late in the season. Growers should maintain good canopy aeration, minimize berry damage and carefully observe preharvest intervals for any crop-protection products. Harvest decisions should ultimately balance technological and physiological maturity with fruit health and weather conditions. Close communication between growers and winemakers becomes increasingly important as harvest approaches so that fruit can be picked at the optimal stage for its intended use and delivered rapidly and in good condition to the winery.

For more detailed guidance on harvest decisions, please consult the two recently published MSU Extension newsletters addressing fruit chemistry and harvest maturity in Vitis vinifera and hybrid cultivars. These articles discuss the key chemical and physiological parameters used to assess fruit maturity and provide practical guidance for determining the optimal time of harvest.

For Vinifera cultivars: Ready to pick? Preparing for harvest and evaluating wine grape quality in Michigan

For Hybrid cultivars: Beyond cold hardiness: Managing fruit quality and harvest maturity of hybrid wine grapes in Michigan.

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

Current insects to look out for include leafhoppers, berry moth, yellow jackets, and vinegar flies Scouting vineyards now is important to make sure you have these under control. We saw some vineyards this week that had very high leafhopper abundance and declining effective leaf area. Important to stop that level of damage now so the leaves have a chance of ripening the berries.

For cultivars with tight clusters that are prone to rots, we recommend protecting from sour rot using sterilants such as Oxidate or Jet Ag, or ProBlad Verde to manage the pathogens. Including an insecticide can help limit these outbreaks by stopping the vinegar flies from moving the pathogens. Talk to your winemaker about potential restrictions on late-season treatments, and check the E-154 guide for recommendations.

This week, MDARD reported a detection of spotted lanternfly (SLF) in south Berrien County, the first in Southwest Michigan. It’s important to highlight that this detection was in a park and NOT in any vineyards. This article provides an overview of MSU’s information on this pest: Spotted lanternfly is spreading in Michigan, and MSU Extension is helping Michiganders prepare. MSU Extension will be sharing more information on this pest during winter meetings.

Bird damage and management

Bird pressure typically increases at veraison, when berries begin to soften, develop color and accumulate sugar, making ripening fruit increasingly attractive to birds. Once birds discover a vineyard and begin feeding, they can be difficult to discourage, so growers should begin monitoring and implementing control measures before or at the onset of veraison, particularly in high-value blocks and vineyards near woods or other bird habitat. Without effective control, bird feeding can result in substantial crop losses.

Bird netting remains one of the most reliable methods of protecting ripening fruit because it provides a physical barrier between birds and clusters. Other approaches include reflective streamers, scare devices, electronic distress calls, propane-fired bird-scaring cannons, predator-shaped kites, UAVs and laser-based deterrents. Visual or acoustic deterrents are generally more effective when combined and periodically repositioned or changed, since birds may become accustomed to a single deterrent over time.

Growers should also remember that bird injury can create open wounds on berries, increasing susceptibility to Botrytis bunch rot, sour rot and associated insect activity as fruit approaches harvest. Regularly scout clusters for bird feeding and berry injury, especially as sugar levels rise, and integrate bird management with late-season disease and insect management programs, as explained in this article from MSU Extension.

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 SAM Tool helps Michigan grape growers organize day-to-day vineyard operations, including scouting, spray and non-spray activities, task assignments, communication with workers, and recordkeeping. Managers can plan and track vineyard activities from their computer, while the mobile app allows workers and managers to access tasks and record information out in the vineyard. The SAM Tool is available at sam.msu.edu.

What's New in the SAM Tool? Recent updates continue to improve day-to-day vineyard management. Finding the tasks you need is now faster with an enhanced Management page. When viewing past and current Tasks, users can search activities using a flexible date range, the system automatically remembers each user's preferred filter settings, and the default view focuses on tasks from the current year. These improvements reduce the time spent navigating records and make it easier to find and duplicate previous tasks for future planning.

If you have any questions about the SAM Tool or would like to participate in the Yield Estimation Modeling for Michigan Winegrapes research project, please send a message to the SAM Tool team at sustainableag@msu.edu. 

Events and announcements

Join the Great Lakes EXPO Grape Session for practical updates on priority vineyard insect pests, vineyard technology, canopy management, and grape disease management, including spore trapping, diagnostics, and fungicide resistance. Two RUP credits will be available. For more information, contact Esmaeil Nasrollahiazar at nasroll2@msu.edu. 

Related articles

• Maximizing grapevine canopy potential: Optimizing pre-bloom shoot thinning and positioning
• Early hedging for healthier canopies and better ripening in cool climates
• 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