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 state climatologist.  

Report on growing degree days (GDD)  

• Southwest Michigan GDD summary from March 1 through July 4, 2024  
• Southeast Michigan GDD summary from March 1 through July 4, 2024  
• Northwest Michigan GDD summary from March 1 through July 4, 2024  

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 

Clusters in southwest Michigan are expanding rapidly with the recent warm weather and good soil moisture. Bunch closure on Vignoles has been observed in southwest Michigan vineyards, and canopy development is advancing.  

Northern Michigan 

Northern Michigan's vineyards are making significant progress in grape growth. In the grape-growing regions of northwest Michigan, bloom time has come to an end. The clusters on all vinifera cultivars have entered the fruit set stage (Photo 1). Notably, in the northwest region, vine shoots have grown above the top wire, indicating the need for canopy management practices such as late leaf removal to ensure optimal vine growth. 

Tip of the Mitt region 

In the Tip of the Mitt region, hybrid cultivars have set fruit and are currently in the peppercorn to pea-sized berry stage of development. However, fruit set is variable, with some cultivars exhibiting excellent yields while others show uneven set, likely due to the recent heavy rain and strong winds (Photo 2). Vinifera grapes are still in the flowering stage, with 60-75% of the flower caps having fallen off (capfall).  

See this chart for grape growth stages. 

Horticulture 

Vineyard hedging is set to commence soon in Michigan, aiming to achieve several key objectives. The primary focus 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 robust 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, a stage when primary and lateral shoots start bending at a 45-degree angle. 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. 

Additionally, some juice grape vineyards have reported instances of over-cropping. Effective crop load management plays a pivotal role in achieving the desired Brix level. An excellent tool to assess crop load is the Concord model on Michigan State University’s Enviroweather. Conducting cluster thinning at 1,500 GDD is recommended. 

Diseases 

During this time of 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, refer to a grape scouting report from earlier or explore 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. 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 F 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  

A second site in Michigan has been found with live spotted lanternfly, as announced by the Michigan Department of Agriculture and Rural Development this week. The site is in southern Monroe County just north of Toledo, Ohio, and is not near fruit agriculture. Michigan State University is working with a network of agencies monitoring sites across the state, and these include multiple vineyard locations. Growers can help out by staying vigilant for these invasive insects and reporting any suspect detections to the Department of Natural Resource’s Eyes In The Field.   

Grape berry moth larvae can be found in grape clusters in southwest Michigan vineyards, especially those with low cropload that have not been treated with insecticide yet. Scouting vineyards along the edges and into blocks can quickly show whether your locations also have activity of grape berry moth larvae currently, and what stage of development they are at. Some insects develop more slowly when it is extremely hot, but we don’t yet know how to adapt the grape berry moth model for extreme heat days, so it has been accumulating heat units quickly during this warm spring.   

The second generation of grape berry moth is underway in southwest Michigan vineyards, earlier than usual. Based on the conditions in your region and the vineyard cropload, consider the need for repeat applications during this period to protect clusters from grape berry moth. Products with extended activity and those with performance under high heat and sunlight conditions should be considered given this year’s weather and the extended egglaying from berry moth during the summer. 

This week during visits to vineyards in southwest and northwest vineyards, there was evidence of Japanese beetle feeding, grape berry moth larvae and phylloxera galling on hybrid vine leaves (southwest region). In the northwest region, we observed rose chafer, potato leafhopper nymphs, lacewings and ladybeetles, and the larva depicted in Photo 3. Even if a vineyard isn’t being harvested, we recommend continued scouting for these insects to observe what is present and at what levels. Neonicotinoid insecticides such as Assail and Admire Pro can provide protection against leafhoppers, beetles and tumid gallmaker if present in the same vineyard site. 

SAM Tool for vineyard management   

The Sustainable Agricultural Management (SAM) Tool is a comprehensive software application designed to assist grape growers in managing vineyards more effectively. Please sign up to access the SAM Tool. The application is developed by Karen Chou of Michigan State University (MSU) Extension in collaboration with MSU’s Department of Computer Science and Engineering. Dennis Phillips is the lead software developer.  

The application offers a range of features designed to save time and enhance vineyard management efforts. It employs robust data security and accuracy measures and can be used for mapping sub-fields, generating auto-populated spray records, and issuing warnings about the consecutive use of the same pesticides to minimize the development of pesticide-resistant pests.  

Additionally, the app displays your spray tasks on a calendar and helps to identify restricted entry fields and manage preharvest sprays using the restricted-entry interval and preharvest interval databases. It also facilitates task assignments, sends task reminders for managers and workers, and allows the upload of photos and scouting notes directly from the field, which can be viewed later within the application.  

You can also help the Michigan Wine Collaborative pilot the Michigan Vine Balance Workbook, a sustainability certification program, through the website. Please fill out this brief survey to answer one question and enter your contact information for Chou to offer you personalized guidance on beginning to use this application.  

Upcoming events  

Parallel 45 Vines & Wines Pre-Veraison Meeting: Boost Grapevine Productivity. Gain valuable insights from industry experts at our upcoming hybrid meeting on July 12. We'll focus on presentations about compost tea, biochar and organic compost from Krull's. Don't miss out – pre-registration is required!  

The 35th annual Michigan Viticulture Field Day and inaugural Michigan Enology Experience are approaching. MSU’s famous field day and steak dinner is back on July 31. We are now adding a second day just for the winemakers.  

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.  

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