Michigan grape scouting report – June 1, 2022

Grape bloom has begun in southwest Michigan.

closeup of juvenile grapes
Several hybrid wine grapes have begun blooming at SWMREC: Marquette, Geneva Red, and Brianna (pictured). Photo by Mike Reinke, MSU Extension.

Weather

Last week started mild. Southern Michigan saw high temperatures near 60 degrees Fahrenheit at the start of the week, slowly climbing into the upper 70s by the weekend. Northern Michigan saw a similar trend but climbing to the low 70s. A dome of heat entered the state over the weekend, bringing highs near 90 on Monday and Tuesday.  

Scattered rain passed through the state on Wednesday and Thursday, bringing a quarter to half inch of rain for most areas. Another intense storm system slowly passed through the middle of the state on Friday morning, dropping up to 2 inches in some isolated locations. A storm front blew through the state last night bringing cooler air with it. 

The next week will bring mild and consistent weather. Northern Michigan should see high temperatures in the mid 60s, lows around 50. Southern Michigan will have highs in the mid 70s. Sunday and Monday will see chances of rain, but at this time, there are no predictions for severe weather with the system. 

With the warmer week, we picked up an average number of GDD than last week: 75-110 GDD base 50. The southwest region is 180 GDD base 50 ahead of the northwest region. 

Region

Current GDD 50 F 

GDD 50 F last week

Collected the past week

Southwest Michigan

480

369

111

Southeast Michigan

431

325

106

Northwest Michigan

300

225

75

Vine growth

In the southwest, juice grape varieties and many hybrids are at prebloom stage. Some hybrids such as Marquette, Geneva Red, and Brianna started blooming on Tuesday at the Southwest Michigan Research and Extension Center (Benton Harbor). Most vinifera are around 12-15 inches of growth at this time with clusters beginning to expand and separate.

In northern Michigan, growth continues with many varieties adding  2-4 inches of growth. Unfolded leaves and clusters can be seen in most of the cultivars.

See this chart for grape growth stages.

 

GR-May 30, 2022 copy
Current shoot growth in northern Michigan. Photo by Esmaeil Nasrollahiazar, MSU Extension.

 

 

Horticulture

Shoot thinning should be underway in earlier varieties in the southern vineyards, with later varieties beginning soon. 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. 

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

Horticulture

Shoot thinning 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. 

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

GR-20220531_riesling
This is the time to begin shoot thinning in southern Michigan. Photo by Mike Reinke, MSU Extension.

Diseases

At this time of year, the disease focus is on phomopsis, black rot, anthracnose and powdery mildew. Contact fungicides like the EBDCs (FRAC M3) and captan are the prebloom products of choice. They function similar to dormant applications by sanitizing the vineyard before bloom. 

Copper, sulfur and early season oils may also be utilized (especially if a grower is organic), which try to suffocate fungal spores and infected tissues or kill on contact. Be careful when using oil with certain products as it can increase the risk of phytotoxicity. 

As bloom approaches 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. For more information on fungicide options and the impacts of rain on disease spread, check out last week’s grape scouting report or this article on early season disease management.

GR-Phomopsis leaf lesions observed June 1_Miles
Phomopsis foliar lesions were recently observed in a high pressure vineyard on June 1. Photo by Timothy Miles, MSU Extension.

Insects 

High grape berry moth catch continues in southwest Michigan. These moths being caught are males. Females should be emerging as grapes begin to bloom.  

Wild grape bloom has become widespread throughout southwest Michigan in the past week. Reports started coming in of bloom on Friday and continued through the weekend. Wild grape bloom at 50% is used as the biofix for grape berry moth models. The majority of the grape berry moth population is not in within commercial vineyards at this time of year. So any insecticide treatments will have no measurable impact on future generations. Typical treatment timings usually start with the next generation that will show up in 4-6 weeks. 

For southern Michigan grape growers, be on the lookout for rose chafer and potato leafhopper. Both should be expected in vineyards soon. Rose chafers can be found feeding on leaves and clusters. Potato leafhoppers feed on the undersides of leaves. The leaves of some sensitive grape varieties can be yellowed and cupped in response to this leafhopper’s feeding. Most vines are very tolerant of their damage and control isn’t warranted. Potato leafhopper does not overwinter in Michigan. It is blown in on southerly winds and storm fronts in the spring.

Upcoming events

  • The Michigan Grape Society Summer Grower’s Social series continues on June 15 with 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, 2022) 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 information to come soon.

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