Michigan grape scouting report – September 21, 2022

September is a key month for Michigan grape growers and it is the time to focus on disease and bird management to protect clusters. Sour rot and botrytis are being reported around the state.

Photo 1. Photo by Jackie Perkins, MSU.


Click below for detailed seven-day forecasts for various grape production regions.




The grape growing regions in Michigan had almost the same growing degree day (GDD), indicating that the southern grape growing regions had a cooler week than usual, with only 11 GDD based on 50 degrees Fahrenheit difference between the coolest and the warmest Michigan AVAs.

Southwest Michigan GDD summary from March 1 through Sep 19, 2022
Southeast Michigan GDD summary from March 1 through Sep 19, 2022
Northwest Michigan GDD summary from March 1 through Sep 19, 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

Harvest for hybrid wine grapes has completed in southwest Michigan and is continuing for vinifera varieties, while harvest for early varietals has begun in the northwest. Most vineyards in the Tip of the Mitt AVA have already harvested a variety or two, and this is expected to continue this week (Photo 2), especially with a dry week on the way.

See this chart for grape growth stages.

A winemaker removing fruit from a vineyard.
Photo 2. Josh Morgan, the winemaker at Petoskey Farms Vineyard and Winery, is featured in the photo, with some Itasca fruit taken from the Blu Dot. Photo by Paul Silva at Blu Dot Vineyards.


Northwest region (Brix)

Southwest region (Brix)







Pinot noir



Pinot Blanc



Pinot Gris



Cabernet Franc





Not available



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Hundreds of bird species choose Michigan as a migratory path, causing significant damage to grapes and other late-season fruits. Because all grape varieties have more than 15 brix at this time of year, it is critical to control bird damage, which could be expected to begin and increase as fruit ripens.

If you haven't noticed any damage yet, don't think you're safe because birds will harvest your berries a day or two before you are. The most effective kind of defense is netting. Inflatable "used car lot" balloons, propane cannons, laser bird repellents, and auditory fright calls are occasionally utilized as well, but their efficacy is debatable and their nuisance factor is high. Please check out this article for more information.


Weed control is important at this time of the year for both harvested vineyards and blocks yet to be harvested. Weed control in non-harvested vineyards is mainly important to reduce weed interference in machine or manual harvest and to reduce the soil weed seed bank for the following season.

The application timing for most of the herbicides before harvest is mainly based on the pre-harvest interval (PHI). Aim (three-day PHI), Rely (14-day PHI), and Gramoxone (Restricted Use Pesticide) provide quick burn-down of weeds. Rely and Gramoxone control both broadleaves and grasses, but Aim is only effective for broadleaves. Venue (zero-day PHI) can be added to improve burn-down and broaden the weed control spectrum. Some herbicides will damage grape green bark, new shoots, leaves or vines, so minimize contact with vines during application.

Glyphosate also has a short 14-day PHI, but it is not advisable to apply it after bloom. Significant injury may occur during the current season of the following year if glyphosate comes in contact with leaves, green shoots or is absorbed by bark.

After grape harvest, weed control might not be the top priority for many vineyards. But fall is the best time to control perennial weeds and apply residual herbicides to vineyard floors. After harvesting, the most important step is to perform thorough scouting of your vineyard and prepare a list of weeds that are problematic in your vineyard. The next step is to select the herbicides in combination with non-chemical management tools that are effective against these weed species.

Fall applications of preemergence herbicides should be made before the soil freezes. Preemergence herbicides such as Alion (indazaflam), Princep (simazine), Solicam (norflurazon), Casoron (dichlobenil), Kerb (pronamide), GoalTender (oxyfluorfen), Prowl H2O (pendimethalin), Chateau (flumioxazin) and Matrix (rimsulfuron) may be applied in fall.

Detailed information related to the herbicide rates and efficacy on weeds can be obtained in the Herbicide section of E154 Michigan Fruit Management Guide, that contains lists of all currently labeled herbicides along with specific remarks for their use in vineyards.


The disease focus for most grape growers in Michigan is still powdery mildew, downy mildew and cluster rots. Pay close attention to preharvest intervals for specific products. Insect and bird damage and fruit splitting are major contributors to rot development. This week, some southwest vineyards are showing cluster rot symptoms and powdery mildew and downy mildew have been apparent for a while. The time to manage sour rot is now as berries are ripening quickly in southwest Michigan.

At this time, we continue to be concerned about defoliation caused by downy mildew which will reduce vine winter hardiness. This article provides more information on late season downy mildew 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, captan and some biologically-based products.

Several strategies contribute to good botrytis bunch rot management (Photo 3). These include opening up the canopy, properly applying fungicides and using resistant cultivars when possible. Good botrytis control depends on getting good coverage. 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 now available for managing botrytis bunch rot.

Photo 3. Botrytis bunch rot on grape clusters.
Photo 3. Botrytis bunch rot. Photo by Jackie Perkins, MSU.

Sour rot can be particularly difficult to control on tight clustered varieties. Enhancing airflow through the canopy and clusters can help, so leaf pulling, thinning, shoot positioning and weed control can all provide some reduction in sour rot risk. Another important aspect of control is preventing berry damage (e.g., bird pecks, insect feeding and mechanical damage) to reduce the initiation of berry infections. We are finding more cracked berries, too, after the recent rainfall. Combining an insecticide with a contact fungicide can be effective in managing both the insect vector and the pathogen. In high risk cultivars (e.g., Vignoles) and in hot and humid conditions, these treatments should be applied before symptom development and clusters have reached 13-15 Brix. Under high disease scenarios, reapplication may be needed on seven- to ten-day intervals until harvest, with careful attention to pre-harvest intervals.

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 some vineyards in southwest Michigan that we monitor regularly, grape berry moth (GBM) flight activity was lower this week than in previous weeks, with cool nights likely slowing adult activity.

In southwest Michigan, the trap catch average was five per trap, with most traps only having zero to two adults over the last week. Additionally, there was no increase in grape berry moth damage on clusters reported from these vineyards that are being actively treated for grape berry moth protection.

With the cooler temperatures at night, the fourth generation is less likely to be a problem, unless in the sites with very high pressure. If scouting indicates that grape berry moth damage is still increasing on your farm or you are finding new/living larvae then pre-harvest insecticide applications may be required.

In some areas, cracked fruits with wasps, vinegar flies, and ants have been observed. Vinegar flies can lay eggs into cracked or damaged fruits, potentially leading to larvae contaminating fruit. Fly and wasp activity can also contribute to the spread of cluster rots as insects move from damaged clusters throughout the vineyard. Vineyards with vinegar fly populations developing in varieties susceptible to cracking or cluster rots may need some fly control prior to harvest. It is recommended to continue scouting to assess the need for this on your farms as harvest approaches.

Although spotted lanternfly has not been found in any Michigan fruit crops, it was detected in Oakland County recently. Monitoring is underway and traps for early detection have been placed at several vineyard sites and at rest areas along the freeway.

2022 Educational needs assessment survey

The Michigan State University Extension grape team created an educational needs assessment survey to develop an educational plan for 2023. We are looking forward to hearing from both growers and producers to help us meet their educational needs and serve them better.

Please contribute to improving the relevance and quality of education. The poll has multiple-choice questions and takes around 3–5 minutes to complete.

Take the Wine and Juice Grape Educational Needs Assessment Survey

Great Lakes Expo

Grape section agenda

Tuesday, Dec. 6, 2 to 4 p.m.






Improving canopy and trellis systems efficiency for wine grapes in Michigan’s cool climate


45 min

Paolo Sabbatini


Keep calm and carry on scouting for SLF


35 min

Rufus Isaacs


vineyard mechanization aims to reduce grape production costs and labor intensity


40 min

Kaan Kurtural

UC Davis

Talk descriptions

Improving canopy and trellis systems efficiency for wine grapes in Michigan’s cool climate

Paolo Sabbatini, Professor of Horticulture, Department of Horticulture, Michigan State University

Over the past 20 years, several pivotal advancements in vineyard design, trellis and training systems, and canopy management practices have improved productivity and fruit quality in Michigan. Before the last two decades, standard vineyard designs and trellis systems were used throughout the state for hybrids or vinifera grapes, without any consideration for cultivar, site or even rootstock selection. In fact, little attention was paid to site-specific conditions influencing vine growth such as 1) climate, 2) AVAs, 3) soil type and 4) rootstock/cultivar interaction. Recently, significant efforts were made to fit vineyard design and trellis system to the site-specific factors that influence vine vigor and fruit quality at harvest. As a result, different plant densities and training/trellis systems are now adopted in Michigan for wine grape production. The trellises used are ranging from single to divided canopy systems with horizontal and vertical canopy division. Due to both cost, durability, and efficiency in managing and replacing, metal has replaced wood as the material for trellis construction. Climate is the major contributor in vine growth and yield, particularly temperature, annual rainfall, sunlight exposure, and wind velocity; the four Michigan appellations are characterized by striking different climates. Warm summer temperatures and large amounts of sunlight exposure encourage large canopies (southern Michigan AVAs), while cooler temperatures or constant and high-velocity winds in the spring and summer result in less-vigorous growth (northern Michigan AVAs). Soil texture and potential vine-rooting depth also influence vine growth. Deep, fertile soils with large amounts of moisture support vigorous vine growth, while sandy soils with moderate rooting depth and lower amounts of water result in less vine growth. Lastly, pre-plant soil preparation (ripping or slip plowing), cultivar, rootstock selection, and cultural practices (irrigation, fertilization, and vineyard floor management) also impact vine growth and fruit quality.

Keep calm and carry on scouting for spotted lanternfly

Rufus Isaacs, Department of Entomology, MSU

The August 2022 detection of a population of spotted lanternfly (SLF) in southeast Michigan raises the threat level of this insect to our grape industries. Although the detection was not at a vineyard, and no spotted lanternfly have been reported in Michigan vineyards, it will be important for growers to be on the lookout for this pest and for winery staff to be prepared to answer questions given the public awareness of this pest. This talk will review the biology, identification, reporting, and current status of spotted lanternfly and will share up to date recommendations for grape growers.

Vineyard mechanization aims to reduce grape production costs and labor intensity

S. Kaan Kurtural, Department of Viticulture and Enology

The presentation will provide information to growers on vineyard establishment for mechanization, dormant pruning, shoot removal, leaf removal, crop load management, labor operations cost as well as wine composition that can be expected from mechanically managed vineyards.

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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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