Michigan grape scouting report – May 25, 2022

Wild grape bloom is expected soon in southern Michigan. Shoot growth is slow, but continuing in northern vineyards.

closeup of juvenile grapes
Grape growers don’t usually think about modifying their spray programs for pollinators the way many other crops do. But grapes can still be attractive to other beneficial insects like the Chinese mantid nymph seen here on wild grape. Photo by Mike Reinke, MSU Extension.

Weather

Last week was mild in southern Michigan, cold in northern reaches of the state. Southern Michigan saw high temperatures near 60 most of the week with the exception of a short-lived warm up at the weekend when much of Michigan’s southern tier reached the low 80s for Friday and Saturday. Northern portions of Michigan were about 10 degrees colder and only received one day of the brief warmup on Friday.  

The warmup on Friday was due to a warm front that passed through the state. This front also brought thunderstorms and brief, but at times, heavy rain in some locations. Most locations received a half to an inch of rain from this system. 

The next week will continue with high temperatures near 70 degrees in southern Michigan, rising to the mid to upper 80s by the end of the weekend and into the start of next week. Northern wine growing regions will once again be 5-10 degrees cooler. The only major rain predicted should occur today through parts of Friday. The rest of the coming week should be partly to mostly sunny.

With the cooler week, we picked up fewer GDD than last week: 27-76 GDD base 50. The southwest region is 144 GDD base 50 ahead of the northwest region. 

Southwest Michigan GDD Summary from March 1 through May 23, 2022 

Southeast Michigan GDD Summary from March 1 through May 23, 2022 

Northwest Michigan GDD Summary from March 1 through May 23, 2022 

Region

Current GDD 50 F 

GDD 50 F last week

Collected the past week

Southwest Michigan

369

304

65

Southeast Michigan

325

249

76

Northwest Michigan

(NWMHRS)

242

198

27

Northwest Michigan

(Old Mission)

225

194

16

Vine growth

In the southwest, shoot growth has continued at a steady pace. Juice grape varieties and early hybrids are at around 12-15 inches of growth. Clusters are visible and starting to separate. Other hybrids and early vinifera have 8-12 inch shoots. Most vinifera are around 6-8 inches of growth at this time. 

g-20220524_wild grape bloom
Wild grape bloom has been seen in central Berrien County. This is one of the first sites the scouting team sees each year. Most production areas start seeing bloom less than a week later. Be watching for wild grape bloom to show up in southern Michigan as early as this weekend. Photo by: Mike Reinke

In northern Michigan, although last week was a chilly week, most varieties have had good growth, gaining 1-2 inches of additional growth in the last week, putting them at 4-6 inches total. Two-three fully expanded leaves and initial clusters are distinguishable in some early varieties, such as Cabernet France and Chardonnay.

g-May 23, 2022
Shoot growth has been slow in northern vineyards. Many varieties saw only 1-2 inches of growth in the past week. Photo by: Esmaeil Nasrollahiazar

See this chart for grape growth stages.

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. 

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. 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

Insects 

Grape berry moth catch remains high. These moths being caught are males. Males typically emerge before females in the spring. Without females, these males are highly attracted to traps so we get these high catches. Female moths will start emerging as the clusters start blooming in the coming weeks. 

g-PXL_20220523_GBM catch
Grape berry moth males continue to be caught in high numbers in southwest Michigan. The females will start laying eggs once grape bloom begins. Photo by: Rufus Isaacs

Wild grape bloom has been seen in one location so far in Berrien County. Wild grape bloom at 50% is used as the biofix for grape berry moth models. Biofix for this insect has been around the last week of May or the first week of June for many parts of southwest Michigan in recent years.

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.

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