MSU Extension Grapes

Weather 

Click the following links for detailed seven-day forecasts for various grape production regions.   

Southwest  

• Benton Harbor   
• Fennville   
• Lawton   

Southeast  

• Romeo   

Northwest  

• Old Mission   
• Petoskey   
• Traverse City   

See the latest agricultural weather outlook from Jeff Andresen, Michigan State University (MSU) state climatologist.   

Check out the MSU Enviroweather Growing Degree Days (GDD) Michigan map. Find your closest weather station, create an account on the website, and track GDDs daily. 

Report on growing degree days (GDD) 

The following table summarizes the GDD base 50 degrees Fahrenheit for the current week and the previous week, as well as the accumulated GDD for each location.  

Vine growth 

Southwest Michigan 

Veraison is expanding into more vinifera varieties. Several hybrids have completed veraison and are beginning to increase brix levels. Cluster thinning is underway for crop load management especially in spur pruned vineyards, while in cane pruned ones it can be postponed or even avoided if the vines were pruned correctly and to clean out powdery mildew infections that started with the hot weather in June. Powdery and downy mildews continue to be challenging to clean up.

Southeast Michigan 

Veraison has been observed this week in ‘Fredonia’ (up to 22 millimeters) in Romeo (Macomb County). Table grapes in Britton (Lenawee County) that have started veraison include ‘Venus,’ ‘Mars’ and ‘Vanessa.’ ‘Concord’ berries measured up to 22 millimeters in diameter in Fenton and Romeo.

Veraison began in ‘Petite Pearl’ (up to 13 millimeters  berry diameter) in Macomb County the week of July 22, with veraison in ‘Marquette’ (up to 20 millimeters) and ‘Frontenac’ (up to 15 millimeters berry diameter) starting the week of July 18. ‘Itasca’ grapes observed in Ray Township were at 18 millimeters in diameter. Some growers have started putting up bird netting.

RimPro models indicate there is risk of powdery mildew infection from Aug. 10-15 in the region, downy mildew infection risk peaking Aug. 16 and low risk for grape black rot.

Northern Michigan     

Vinifera grapes are showing good progress in their development. In the late-maturing varieties for the northwest region (e.g., Cabernet Franc, Riesling), the berries have reached the pea-sized stage. For the early-maturing varieties (e.g., Pinot Noir, Chardonnay), the berries are at the beginning of bunch closure, a crucial stage where the clusters start to tighten. (E-L numbers 31 -32),

Tip of the Mitt region 

Hybrid cultivars continue to progress into the veraison stage of development. Vinifera are in the bunch closure phase of development with berries beginning to soften. Japanese beetle populations remain high. Canopy management continues. Powdery mildew and downy mildew have been noted in several vineyards. 

Horticulture

Vineyard hedging has been going on for a couple weeks in southern Michigan and should begin soon in northern vineyards. The primary focus for hedging is on curtailing excessive primary and lateral shoot growth on the canopy's top and sides to prevent shading and entanglement between vine rows. By doing so, the vineyard becomes more accessible for workers and tractors. Interestingly, hedging also stimulates growth by promoting lateral shoot development in vigorous vines, despite the reduction of the canopy due to the removal of primary and lateral shoots.

It is recommended to perform hedging during the early to mid-summer period. Ideally, hedging is carried out between fruit set and veraison. This timing is crucial as it ensures adequate exposure of leaves, fruit, and developing buds to sufficient light, especially in dense canopies of hybrid cultivars with excessive vegetative growth. To avoid potential issues, it is essential to refrain from hedging too early in the growing season, as it may lead to increased lateral growth and canopy density.

However, we consistently perform early-season hedging due to late bud break and elevated spring temperatures, which promote vigorous growth early in the season. We always avoid hedging during bloom or shortly thereafter to prevent increased cluster fruit set that consequently increases cluster compactness, making the clusters more prone to harvest season cluster rot complex diseases. Growing grapes in Michigan can be likened to a "100-meter sprint," as Craig Cunningham, an experienced vineyard manager in Michigan, describes it, compared to the marathon-like growing season of other viticultural regions. Typically, we hedge twice: once before veraison, and once after. Hedging three times in a season is unusual and indicates a problem. If your vines require a third hedging, it likely points to issues such as inappropriate rootstock selection, excessive nitrogen levels, or incorrect planting density.

The time of leaf removal is underway or approaching fast, depending on the region. Cluster zone leaf removal at the pre-veraison stage (mechanical or manual) is a critical viticultural practice with significant benefits for grape quality. By removing leaves around the grape clusters before veraison (the onset of ripening), growers can improve sunlight exposure and air circulation within the canopy. This increased exposure to sunlight enhances the development of desirable phenolic compounds and promotes even ripening, leading to better color, flavor, and aromatic profiles in the grapes. Improved air circulation reduces humidity around the clusters, which lowers the risk of fungal diseases such as powdery mildew and botrytis bunch rot, contributing to healthier fruit and reduced need for chemical treatments.

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, we 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 on fruit and leaves. Powdery mildew symptoms are becoming more apparent, so vineyards should be scouted to check on the status of diseases.

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.

Remember, as you choose a fungicide, check the Michigan Fruit Management 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).

It is important to remember to manage fungicide resistance and avoid applying similar products back-to-back. This is particularly important with site-specific systemic fungicides. To reduce the development of resistance with systemic fungicides:

• Do not make more than two applications per season of the same FRAC code.
• Do not make two consecutive applications of the same FRAC code.
• Rotate with unrelated fungicides in a different FRAC code that have efficacy on the target pathogen.
• Include a contact multisite fungicide into a program (e.g., sulfur, captan, oils or biological fungicides).

Since some parts of the state are near veraison, this is also an important time to consider botrytis management. Botrytis has been spotted in many early ripening varieties like Marquette, and sporulation can be seen on infected berries that were likely started by berry moth infestations. Several strategies contribute to good botrytis bunch rot management including opening up the canopy, effective insect control, 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. 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.

Insects

The third generation of berry moth is underway in southwest Michigan, and will be starting in areas further north as August continues. Check the growing degree-day (GDD) model for your region to determine predicted dates for egglaying to start (at 1620 GDD) or for egg hatch (1720 GDD). Generation 3 can be more intense than earlier in the season due to the higher population of grape berry moth, so this treatment at the start of the generation should be followed by another 10-14 days later to continue protection of the clusters toward harvest. This is a great time to look under the canopy at your clusters to see where there is some grape berry moth pressure building and where the vines are uninfested. Targeting border sprays only to reduce costs is one approach to consider if the sampling indicates pressure is only on the edge. Typically, the first ~10 rows get the most pressure from grape berry moth and it tails off after that as you get into the vineyard. Scouting can inform this approach.

As we move into veraison this month, think about those rot-susceptible cultivars and prepare your sour rot management plan. We recommend starting protection from pathogens and the insect vectors at around 15 Brix in these cultivars.

MSU is working with state and federal agencies monitoring sites across the state for spotted lanternfly, including multiple vineyard locations. Growers can help out by reporting any suspect detections to the Department of Natural Resource’s Eyes In The Field.   

Become a legacy user of the SAM Tool and enhance your vineyard management!  

The Sustainable Agricultural Management (SAM) Tool is a comprehensive software application designed to streamline your vineyard management processes. We understand that adopting new technology can be daunting, but we believe the SAM Tool has the potential to transform your vineyard management for the better. This growing season, we are dedicated to offering personalized support. Thanks to the valuable feedback we've received, we continue to shape both the current features and the future of the tool. 

The SAM Tool can manage tasks for a small number of individual vines, as well as large vineyards spanning hundreds and thousands of acres. Your participation as a legacy user will not only help us improve the tool but also provide you with a unique opportunity to be part of an innovative community. Together, we want to ensure it meets your needs and the needs of other Michigan vineyards. 

Ready to get started? Let us help you migrate your spray plan to the SAM Tool and explore the many cool features we've created for you. The SAM Tool can automatically populate this year’s spray tasks into next year’s calendar, allowing you to edit each task to meet the following year’s needs. 

Contact Karen Chou for personalized help migrating your spray plan to the SAM Tool and to help us fine-tune the tool so that it truly meets the needs of growers like yourself. We welcome the opportunity to serve vineyards of all sizes.  

Upcoming events 

Dirt to Glass™ 2024: Elevating Michigan Wine from the Ground Up, Aug. 22-23. Dirt to Glass aims to connect growers and producers each year and provides information to support the Michigan grape and wine industry in understanding the critical relationship between better farming and world class wine. 

As a collaboration between Michigan State University, Michigan State University Extension and industry innovators and educators, this groundbreaking event disseminates the most current research and cutting-edge practical information to elevate the grape and wine industry.  

This year's conference will continue the journey started in 2022, aiming to elevate the Michigan grape and wine industry through a deeper understanding of soil health and fertility, carbon cycle and sequestration, and soil-vine interaction, all crucial sustainability elements in producing high-quality grapes and wines from vineyard to economic sustainability. Each technical session will be complemented by wine educational sessions.  

The Great Lakes Expo: Dive deeper into grapes this year. The Great Lakes Expo, held annually in early December at the DeVos Place Convention Center in Grand Rapids, Michigan, is the largest show of its kind in the country. It attracts a diverse audience of grape growers from the Great Lakes region. 

This year's Grape Section takes place on Tuesday, Dec. 10, 2024. We're offering the Grape Section in two sessions to provide a more in-depth exploration of both juice and wine grapes: 

Morning Session: Focuses on all things juice grapes, covering topics like varieties, cultivation practices and juice production. 

Afternoon Session: Delves into the world of wine grapes, exploring varietals and viticulture techniques. 

This expanded format allows you to tailor your experience to your specific interests, whether you're a juice grape grower, a wine grape producer or simply curious about both. Don't miss this valuable opportunity to connect with industry experts, gain valuable knowledge and explore the latest advancements in the grape growing industry. 

We look forward to seeing you there! 

To get a better sense of the Great Lakes Fruit, Vegetable, and Farm Market Expo, check out this video. 

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  
• 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