Southwest Michigan fruit update – April 18, 2017

Warm weather has moved plants quickly. Peaches and sweet cherries are blooming. Insecticides should not be used during bloom.

Bees resting in a sweet cherry flowers. All photos courtesy of Mark Longstroth, MSU Extension.
Bees resting in a sweet cherry flowers. All photos courtesy of Mark Longstroth, MSU Extension.


Fruit development in southwest Michigan is moving quickly with warmer weather. Last week was warm with high temperatures bouncing from the 70s down into the 50s and then rising to 80 on Saturday, April 15. Lows were generally in the 40s. There were scattered rain showers during the week. Friday and the weekend were warm and mild.

Stone fruit are blooming. There is a noticeable difference in fruit development as you move north in the region with the south much more advanced. Little rain fell across the region and river levels are falling. The ground is moist and water is standing in low areas. Soil temperatures are in the 50s and weeds and turf are growing rapidly.

The weather for this week should be warm with highs in the 60s and lows in the 40s. Widespread rain is likely Wednesday and Thursday, April 19-10, and then clearing and cooler on Friday and the weekend. Weekend lows are forecast to be in the upper 30s, which should not cause any damage. We are about 10 to 14 days ahead of the long-term average for bloom dates in southwest Michigan. For the next several weeks, temperatures below freezing are possible, but less and less likely.

Southwest Michigan GDD summary from Jan. 1–April 16, 2017


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMRC)




Lawton (Lawton)




Fennville (TNRC)




Average for the SW region




Accumulation last week




Tree fruit

Warm temperatures moved tree fruit development quickly. Stone fruit bloom continues. Cold temperatures below 30 are required to damage the tree fruit flowers. See “Freeze damage depends on tree fruit stage of development” by Michigan State University Extension for more information. Warm rains during stone fruit bloom pose the risk of brown rot blossom blight. The passage of a cold front on Wednesday will lower temperatures.

Apricots are in the shuck.

Peaches and nectarines are blooming. Flower density is relatively high. The first flight of oriental fruit moth is expected to begin soon. Growers using pheromone disruption for the first generation of oriental fruit moth should have the disrupters in place by the start of flight, which is usually about apple bloom time. Warm rains encourage blossom brown rot. Long episodes of wetting and temperatures above 50 F favor bacterial spot. Low level of copper helps to suppress bacterial population buildup.

Showy peach bloom

Peaches are in full bloom across the region.

Sweet cherry bloom is starting. Montmorency tart cherry buds are at tight cluster. Tart cherry crop potential for most sites looks good.

Montmorency tart cherry opening

Montmorency tart cherry flower buds are at tight cluster, just beginning to open.

Japanese plum varieties such as Shiro and Vanier are at full bloom to petal fall. European plum Stanley is at first white bud. We have moved into the black knot infection season when overwintering knots release spores and infect succulent green twigs of the current season's growth. Use fungicides to protect against infection occuring during wet periods with temperatures above 55 F, especially from white bud to shuck split. Thorough pruning of black knot and disposal of the knots by burning is important in addition to fungicide treatment.

Early-developing apple varieties such as Zestar and McIntosh are at early king bloom. Other apple varieties are at pink. Scab ascospores trap catches have been increasing. Powdery mildew management on susceptible varieties typically begins at pink with the most susceptible period right after petal fall, which coincides with rapid leaf growth of trees. Only new unfolding leaves are susceptible to infection.

Jonathon apples at tight cluster

Jonathon apples at tight cluster, almost to pink bud.

Pear flower buds are at white bud. Kieffer pears, which are common on the roadside, are in full bloom. Fungicide applications for pear scab are ongoing. With bloom, the risk for fire blight increases with warm and wet conditions.

Bartlett pears at white bud

Bartlett pears at white bud.

Small fruit

Grapes are at early scale crack in Van Buren County. Concord and Niagara are at early bud swell in Berrien County. In hybrid grapes, we have early bud swell for early varieties such as Foch. There is no movement in vinifera wine grapes such as Riesling. Dormant sprays can still be made of copper or sulfur products until bud break. This application reduces this season’s disease pressure of downy mildew, black rot, phomopsis and powdery mildew.

Grape flea beetles and climbing cutworm will begin feeding now on sites where they are present. Sites with a history of bud damage should be scouted for blackened or hollowed out buds. Treat if above thresholds of 2 percent for cutworm, 4 percent for flea beetle. The risk of freeze injury to buds is very low.

Blueberry flower buds are tight cluster. Leaf tissue is emerging from the leaf buds of the shoot. This exposed green tissue is susceptible to mummy berry shoot strikes. Growers should be scouting for mummy berry trumpets in areas where mummy berry has been a problem. Many growers have applied Sulforix and other lime sulfur products to suppress early season diseases. Growers have also applied early-season fungicides to protect against mummy berry shoot strike. When the rains and flooding in blueberry fields subside, it will be time to apply spring herbicide treatments to reduce weeds in the bush rows.

Duke blueberries at tight cluster

Duke blueberry buds just after bud burst at tight cluster.

Strawberry leaves are still emerging and flower trusses are sometimes visible in the crown. Strawberry flower buds should be able to withstand 10 F as long as the flower truss is still below ground. Over-wintering mulches should be removed, and rake between the rows. Growers should have their sprinklers set up for frost control when colder temperatures return and flower buds are vulnerable to freeze injury.

Bramble leaves are unfolding. Dormant pruning should be finished and lime sulfur sprays for anthracnose should be on. If you still need to apply lime sulfur, reduce the rate.

Raspberry leaves unfolding

Raspberry leaves unfolding.

Upcoming meetings

Our next Monday fruit IPM meetings is 5 p.m. on Monday, April 24, at Fruit Acres Farms, 3452 Friday Rd, Coloma, MI. Two Michigan RUP applicator recertification credits are available at these meetings.

A Spring Pollinator Conservation Practices Meeting will take place at 3 p.m. on April 27 at the Southwest Michigan Research and Extension Center.

Plan to attend a Blueberry Prebloom Meeting in Van Buren County at 5:30–7:30 p.m., Thursday, April 27, at Haven Harvesters in South Haven, Michigan. The meeting sponsors, Haven Harvesters LLC, New Age/Landmark Laboratories and Bronsink Equipment, are providing a light supper at the beginning of the meeting. There will be talks on early-season insect, disease and weed control, frost control and irrigation by MSU Extension fruit specialists and educators. An online registration form will be available soon.

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