Michigan grape scouting report – June 15, 2022

Watch for disease infections this week. Northern Michigan could see rains several days. Southern Michigan is hot and humid.

Grape vineyard.
Wine grapes in northern Michigan are getting closer to bloom. Many varieties in southern Michigan are at or past bloom. Photo by Derrick Vogel, Petoskey Farms Vineyard & Winery.


It is hot and humid! But, the week started cool. A week ago southern Michigan saw temperatures in the mid to upper 60s. 5-10 degrees cooler in northern grape production areas. Temperatures slowly rose through the week and into the weekend. A dome of high pressure entered the state on Monday, starting in southwest Michigan increasing temperatures into the upper 80s before spreading across the state on Tuesday. Southwest Michigan is experiencing near record heat with high temperatures close to 100 degrees on Tuesday and Wednesday. Southeastern Michigan is seeing the same temperatures on Wednesday and Thursday. Northern Michigan highs are in the mid 80s.

Several rain events passed through the state over the last week, mainly in southern tiers of the state. Most of the rain occurred Tuesday through Thursday of last week. On Monday evening some isolated, severe thunderstorms clipped the southwest portion of the state bringing hail and wind speeds up to 75 miles per hour. Extensive damage is being reported on some crops including grapes in Berrien and Cass counties, but these reports are isolated to the narrow path of the storm cells. In addition to the wind and hail, these storms brought up to 2 inches of rain.

Hail damage to grapes.
The storms that passed through southwest MIchigan on Monday caused isolated, but severe damage. Here is damage observed on concord grapes from the area. Photo by an anonymous grower.

The heat wave in southern Michigan will be short lived. Temperatures should drop back to the mid to upper 70s by Friday. Extended forecasts are predicting temperatures to go back up into the mid 80s next week. Northern Michigan should see even cooler weather with highs only near 70 at the end of the week before climbing back. Southern Michigan should not see any significant rain events over the next week, but northern portions of the state are expected to see rain at the end of the week and through the weekend.

With cooler temperatures last week, we picked up fewer growing degree days: 53-102 GDD base 50. The southwest region is 260 GDD base 50 ahead of the northwest region. 

Southwest Michigan GDD Summary from March 1 through June 13, 2022 
Southeast Michigan GDD Summary from March 1 through June 13, 2022 
Northwest Michigan GDD Summary from March 1 through June 13, 2022 

Enviroweather station

Current GDD 50 F 

GDD 50 F last week

Collected the past week

Benton Harbor (SWMREC)












Average for southwest Michigan








Average for southeast Michigan




Old Mission








Traverse City (NWMHRS)




Average for northwest Michigan




Vine growth

In southwest Michigan, juice grapes are near the end of bloom as are some hybrids. Early hybrid varieties such as Marquette and Brianna are close to buckshot berry at the Southwest Michigan Research and Extension Center. Other hybrid wine grapes and many vinifera varieties are in early bloom now.

In northern Michigan, clusters are expanding on all vinifera cultivars. Shoot length is either in the 6-to-10-inch range for the later cultivars or 12-to-18-inch range for earlier cultivars. In the Tip of the Mitt region hybrid cultivars are in the immediate pre-bloom phase showing well developed inflorescence but no sign of flowering quite yet. Vinifera is in the 10-to-16-inch phase. 

See this chart for grape growth stages.

Current state of cluster growth.
Current state of cluster growth in northern Michigan. Photo by Esmaeil Nasrollahiazar, MSU Extension.


Shoot thinning and trunk cleaning should be underway in many varieties in the southern vineyards. Northern vineyards should begin thinning soon as well. Shoot thinning is an important canopy management tool to improve air circulation, minimize disease pressure, reduce shading, improve spray penetration and ultimately improve fruit quality at harvest. Thin shoots when they are 5-12 inches long and still easy to break off from the woody tissues.

See this article on Early Season Vineyard Management for more information on shoot thinning.


At this time of year, the disease focus is on phomopsis, black rot, anthracnose and powdery mildew. For more information on pre bloom fungicide options and the impacts of rain on disease spread, check out this previous grape scouting report or this article on early season disease management. This week some growers have been finding sparse downy mildew infections in vineyards.

As bloom continues in southwest Michigan, start choosing fungicides that control all the fruit diseases. For example with downy mildew we are most concerned with fruit infection at this time and sprays should be timed prior to bloom and at bloom for optimal control. Downy mildew is caused by a fungal-like organism, so many site specific systemic fungicides that target other spring diseases do not work on downy mildew. Effective fungicides for downy mildew include products in FRAC codes 4, 11, 21, 40 and 45 as well as phosphorus acid salts and some biologically-based products.

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.


Grape berry moth egg laying has continued during bloom and some webbing and larvae have been observed on young clusters. Sites with the highest activity are now showing some GBM larvae starting to form webbing in the clusters. This is easily scouted for by walking along a wooded edge where there were host-spots last season. A sample of 100 clusters can tell you what % cluster infestation is present. If more than 5% of clusters are infested with larvae (evident by their webbing), treatment with an effective insecticide can reduce populations in this early part of the season. Through the season, this approach can be repeated at areas around the farm to track GBM development. Selecting some different sites at vineyard edges and interiors can provide a view of this pest across your farm.  

This time of the year is also when we see some other pests starting their activity. In vineyards with a history of grape tumid gallmaker or rose chafer, keep a close eye over the next few weeks on vineyard areas that  have been infested previously. Tumid gallmaker is starting to show up on some hybrid wine grapes. For tumid gallmaker, application of Movento or Assail at the first sign of gall formation can help reduce their infestation. Small growers can also physically remove affected shoots and clusters, and dispose of them outside of the vineyard. 

Rose chafer activity usually picks up during bloom, so be scouting for these, especially in sandy sites. If they are feeding only on the leaves there is little need for control, except in extreme cases, since vines have the rest of the season to develop the canopy. If feeding is on the clusters, however, those can be protected with an application of insecticide to protect the young clusters. The activity period of rose chafers is quite short, so one application is usually sufficient.

Upcoming events

The Michigan Grape Society summer Grower’s Social event scheduled for this week has been postponed until next Wednesday, June 22, due to clean up from Monday’s storm. The event will still include an evening get together at Domaine Berrien. They will be discussing vineyard weed control, vineyard floor management, and how their practices help prevent winter damage. Registration is required to collect a head count for food.

The Southwest Michigan Viticulture Field Day will return to the Southwest Michigan Research and Extension Center for 2022. As tradition holds, the event will be the last Wednesday of July (July 27) and will include presentations of ongoing research in southwest Michigan. The event will once again conclude with a steak dinner and local wine tasting. Registration for the Viticulture Field Day is online through the Michigan Grape Society’s website.

Register for Dirt to Glass 2022: Elevating Michigan Wine from the Ground Up. Michigan State University Extension is hosting a new conference for the Michigan grape and wine industry. Dirt to Glass 2022: Elevating Michigan Wine from the Ground Up is the first ever of its kind in Michigan and this year it will take place in Traverse City on Aug. 25-26. This year's Dirt to Glass conference will focus on soil health, soil identification and soil fertility. Each year, the conference chooses a specific area of study based on the results of an annual educational needs assessment survey. Registration by July 10 is required.

Extracurricular enjoyment

Calling all vineyard pet owners!

Do you have a photogenic vineyard dog or cat?

Maria Smith (OSU), Annie Klodd (UMN), and Cain Hickey (PSU) are assembling a 2023 vineyard pets calendar as a fundraiser for viticulture scholarships, and would like to feature your vineyard pet. This project came about after years of Maria and Annie meeting so many great dogs on their vineyard visits and discussing how fun it would be to have a calendar of them.

The American Society of Enology and Viticulture is seeking to represent pets from across 13 Eastern U.S. states. One pet for each state will be featured each month and one for the cover. If you are interested in having your pet featured on the calendar, please send a high-resolution photo of your pet in the vineyard to Maria Smith (smith.12720@osu.edu). Please include your name, your vineyard name, and your pet’s name along with the photo by June 30 to be considered. Pets of all kinds are welcome!

Calendars will be made available for purchase, and all proceeds will be donated to the American Society of Enology and Viticulture-Eastern Section Scholarship Fund, which supports viticulture and enology students.

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This work is supported by the Crop Protection and Pest Management Program [grant no 2021-70006-35450] from the USDA National Institute of Food and Agriculture.

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