Michigan grape scouting report – July 27, 2022

Hedging at the right time can maintain your canopy young and active at the end of the growing season.

Wine grape vineyard.
Photo 1. Photo by Rufus Isaacs, MSU.


In northwest Michigan, there is a 30% chance of showers after 2 p.m. on Thursday, July 28. Mostly sunny, with high temperatures around 77 degrees Fahrenheit. There is a risk of showers on Thursday before 8 p.m. and a low of 59 F is forecast. It will be mainly sunny on Friday, with a high around 75 F. Friday night will be clear, with a low around 58 F. Saturday will be sunny, with a high near 83 F. Saturday night will be mostly clear, with a low around 6 F. It will be sunny and around 85 F on Sunday.

In southwest Michigan, Thursday will be sunny, with a high near 79 F and a 30% chance of precipitation. Thursday, there is a possibility of showers and thunderstorms, especially from 11 a.m. to 2 p.m. Partly sunny, with a high near 79 F. Thursday night will be partly cloudy with a low around 64 F. There will be a chance of showers and thunderstorms possible before 8 p.m. Friday will be sunny, with a high near 75 F, and Friday night will be mostly clear, with a low around 62 F. Saturday will be sunny, with a high near 79 F. Saturday night will be mostly clear, with a low around 63 F. Sunday will be sunny, with a high near 82 F.

In southeast Michigan, Thursday will be mostly sunny, with a high near 84 F, and there is a chance of showers after 3 p.m. Thursday night will be partly cloudy, with a low around 58 F and a 30% chance of showers and thunderstorms before 9 p.m. Friday will be sunny, with a high near 78 F. Friday night will be mostly clear, with a low around 56 F. Saturday will be sunny, with a high near 82 F. Saturday night will be mostly clear, with a low around 60 F.

Sunday will be sunny, with a high near 86 F, and at night it will be partly cloudy, with a low around 63 F.

Last week, southeast AVAs were the warmest grape growing areas in Michigan, picking 178.5 growing degree days (GDD), 35.5 GDD more than the previous week. The southwest AVAs were the second warmest regions on average and picked up 171 GDD, while northwest Michigan picked up 160 GDD. The Tip of the Mitt AVAs in Michigan, as usual, was the coolest region, with an average GDD of 162.

Southwest Michigan GDD Summary from March 1 through July 25, 2022
Southeast Michigan GDD Summary from March 1 through July 25, 2022

Northwest Michigan GDD Summary from March 1 through July 25, 2022

Enviroweather station

Current GDD 50 F

GDD 50 F last week

Collected the past week

Benton Harbor (SWMREC)












SW Average








SE Average




Old Mission








Traverse City (NWMHRS)




NW Average




Vine growth

In the southwest AVAs, grape clusters are at berry touch or bunch closure. Some wild grapes are at early veraison. Early hybrid wine varieties should be entering veraison soon.

In the northwest AVAs, wine grape cultivars’ clusters are developing and berries are at buckshot berries and are approaching pea size. In the Tip of the Mitt, most hybrid cultivars’ berries are still hard and green but are starting to show signs of softening.

See this chart for grape growth stages.


Hedging is going to begin in vineyards in Michigan soon. The main objectives of hedging are to cut back on extra primary and lateral shoot growth on the top and sides of the canopy to avoid shading and shoot entanglement between vine rows to make the vineyard more accessible to workers and tractors. Hedging can further encourage growth by promoting lateral shoot growth in robust vines, even though it indirectly reduces the canopy by removing primary and lateral shoots. Hedging is best done in the early to mid-summer.

Hedging is typically done between fruit set and véraison, when primary and lateral shoots begin to bend (at a 45-degree angle). It is critical to keep leaves, fruit and developing buds exposed to enough light in dense canopies with excessive vegetative growth. Avoid hedging too early in the growing season because it can lead to increased lateral growth and canopy density.


In the southwest, disease management of downy mildew, powdery mildew and botrytis fruit rot are the primary focus currently. The heavy dews we are experiencing means it is important to maintain protection against downy mildew. With tight clustered varieties, this is the last chance to get botrytis bunch rot sprays into the tight crevices of the clusters. In the northwest disease pressure is still low but continues to increase in specific areas where black rot is becoming more apparent (Photo 2).

Black rot on fruit and leaves.
Photo 2. Black rot fruit and leaves symptoms, East Lansing, Michigan. Photo by Timothy Miles, MSU.

In this growing stage, consider choosing fungicides that control all the foliar and fruit diseases. For example, with downy mildew we are most concerned with foliar infection at this time and sprays should be timed regularly throughout the season when we experience heavy dews 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.

If powdery mildew is the only concern, there are a number of products that are effective (FRAC codes 3, 7, 11, 13, U8, 50, and U13 as well as sulfur). Combining fungicides from different FRAC classes should also be effective while helping with resistance management.

As we approach bunch closure in the southwest, it is important to consider botrytis management. Several strategies contribute to good botrytis bunch rot management including opening up the canopy, 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. Fungicide resistance management is also important. 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.

Remember as you choose a fungicide, check the 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).


At vineyards in southwest Michigan scouted this week, there was a wide range of grape berry moth infestation. Many of the vineyards we sampled had low pressure, with spray programs effectively protecting the berries from infestation. Others had missed some spray timings, or the applications had been made just before a rainfall event, and protection in those sites was compromised leading to higher infestation (Photo 3).

Grape berry moth damage on grape clusters.
Photo 3. Grape berry moth damage on clusters. Photo by Jackie Perkins, MSU.

For high pressure sites, continuing to maintain protection of berries will be important as vineyards transition into August and the third generation of grape berry moth starts. Looking at the model posted on MSU Enviroweather, the start of egglaying by the third generation is predicted for Aug. 3, so growers using insect growth regulator (IGR) insecticides such as Intrepid or Intrepid Edge should use this timing to treat and protect berries in high pressure sites.

For contact insecticides and those with a stomach poison mode of action, they should be timed a little late for the 1,720 GDD timing to protect the clusters. It is also critical that these applications are followed up with another cover spray to hit the peak of grape berry moth egglaying and larval pressure that will happen 10-14 days later. This should prepare growers for the harvest season with vineyards that can have lower risk of damage in the pre-harvest window.

After the 2021 experience, we are carefully watching vineyards with weekly scouting and growers should be doing the same to make sure that cluster rots and vinegar flies do not develop to be too much of a challenge. We are already primed for seeing some late-season grape berry moth pressure in southwest Michigan given the early start to the third generation, and the long-lead weather forecast also calls for warm evenings.

Continue to monitor this as we approach harvest and be prepared to control rots and their vinegar fly vectors with treatments once the berries reach 14 Brix. A future Michigan State University Extension article will review our recent results on this topic and recommendations for the post-veraison part of the season.

Grape leafhoppers and thrips damage (Photo 4) have also been observed in some vineyards recently. See this article for more information on grape berry moth biofix.

Thrips damage to berries.
Photo 4. Thrips can cause damage to very young berries as early as fruit set. Photo by Rufus Isaacs, MSU.

All species of leafhopper feed by puncturing cells and sucking out the contents on the undersides of leaves. In comparison to hybrid or vinifera grape varieties, juice grape (labrusca) varietals are typically far more tolerant of leafhoppers, but the populations are starting to build in some sites on the interior leaves. Check inside juice grape canopies now to see if your site needs to consider these insects when planning for the next insect control spray. Correct product selection can help get leafhoppers and berry moth.

Thrips damage has also been reported from Leelanau and Grand Traverse counties. Thrips can scar very young berries as early as fruit set. Later, the scars can restrict berry growth, resulting in oddly shaped or scarred berries. Thrips can cause damage to shoots and leaves in the spring, but this is typically more of a cosmetic injury and rarely has economic impact.

Japanese beetles feeding on foliage have been reported in Leelanau, Grand Traverse and Emmet counties and the southwest AVAs. Japanese beetles have only one generation per year, but these beetles emerge over a long period from late June through August, and they live for over 30 days. They feed on the foliage and fruit of various fruit crops grown in Michigan. Read here for more detail: Managing Japanese beetles in fruit crops.

Upcoming events

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 August 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.

Tile Drainage Field Day 2022. Linking Soil Health, Nutrient Management, and Water Management for Improved Water Quality. The event will be hold on Thursday, Aug. 25, 2022 at 13000 Bird Lake Rd., Camden, MI 49232.

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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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