Southwest Michigan fruit update – May 2, 2017

A wet and rainy weekend has set the stage for diseases. Growers are struggling to maintain fungicide coverage.

Blueberry bloom has begun. Image courtesy of Mark Longstroth, MSU Extension.
Blueberry bloom has begun. Image courtesy of Mark Longstroth, MSU Extension.


Last week started warm with highs rising into the 80s on Wednesday, April 26. Cooler and rainy conditions began Thursday with rain through the weekend with highs in the 50s and 60s. Most trees and shrubs have completely leaved with the warm weather the last two weeks and bloom moved quickly in the warm conditions. Passage of a cold front on Monday, May 1, dropped highs to the 60s and rain and thundershowers.

Approximately 1-2 inches of rain fell across the region last week. The ground is wet and water is standing in wet spots. Soil temperatures are in the low 50s.

The weather this week should be cool and wet. Clearing is forecast on Wednesday, May 3. More rain is likely Thursday and Friday. Sunny conditions are forecast for the weekend with highs near 60 and lows near 40. There are lows forecast into the mid-30s this week. Growers should monitor the weather for possible frosts. The weather for the next several weeks is cooler and wetter than normal. We are about a week ahead of the average for bloom dates in southwest Michigan. There is a slight chance of a hard freeze. The Midwest Regional Climate Center posts information on spring and fall freezes.

Southwest Michigan GDD summary from Jan. 1–April 30, 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




Ave from March 1




Tree fruit

Bloom is ending in tree fruit. The wet, rainy conditions were disease infection periods for many diseases. Growers have had a hard time maintaining fungicide coverage with all the rain. Growers can use the Michigan State University Enviroweather Regional Multi-Crop Disease Report to check the duration of the current wetting event across the region. The current wetting period began on April 29.

Freeze damage is still a concern. It would require cold temperatures below 30 to damage the tree fruit. See “Freeze damage depends on tree fruit stage of development” by MSU Extension for more information. The passage of a cold front on Thursday will lower temperatures, but there does not appear to be much risk of a freeze. As the trees leaf out more and more, the leaves increase the amount of heat trapped in the orchard and reduce freeze injury in marginal freezes.

Apricots are out of the shuck. The crop is generally light.

Peaches and nectarines range from petal fall to some varieties in early shuck split. Cool weather is inhibiting insect development. Oriental fruit moth biofix based on trap catch at Berrien, Van Buren and Allegan counties range from April 21 to 24. Oriental fruit moth catches this last week reached over 200 per trap per week for some orchards during the warm days and nights. Using Enviroweather’s Oriental Fruit Moth Model, insect growth regulator insecticides such as Rimon are timed for egg hatch, approximately 100 degree-days (DD) base 45 F from biofix. This was this past weekend for the Berrien County area. Insecticides targeting larvae are timed about 170 DD45 following biofix, which appears to be sometime next week.

Start treating for tarnished plant bug and rusty spot when fruit start to emerge from the shuck. Long episodes of wetting and temperatures above 50 F favor bacterial spot. Applications of low levels of copper helps suppress bacterial population buildup.

Sweet cherries are at petal fall to shuck fall. Montmorency tart cherries are in bloom to petal fall. Tart cherry leaves are unfolding and susceptible to cherry leaf spot infection. Tart cherry crop potential for most sites looks very good.

Sweet cherry fruitlets

Sweet cherries are emerging from shuck. Image courtesy of Bill Shane, MSU Extension.

Montmorency petal fall

Montmorency cherry leaves are out and unfolding and need to be protected from cherry leaf spot. Image courtesy of Mark Longstroth, MSU Extension.

Japanese plum varieties such as Shiro and Vanier are in the shuck. European plums are in the shuck. We are in 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 black knot infection, which occurs during wet periods with temperatures above 55 F, especially from white bud to shuck split.

Apple varieties range from full bloom to petal fall. Temperatures were good for pollination of early- to mid-season blooming varieties in our area Monday through Wednesday last week, but bee activity seems to have been low. Temperatures since Thursday have been too low for effective chemical thinning sprays to reduce crop load. The Cornell University Apple Carbohydrate Model for timing thinning sprays is available in the apple section of MSU’s Enviroweather website.

Apple scab ascospore trap catches are continuing. Apple scab symptoms have been reported from backyard trees, probably from the April 10–12 infection period. Powdery mildew management on susceptible varieties typically begins at pink, with the most susceptible period right after petal fall. This coincides with rapid leaf growth of trees. Only new, unfolding leaves are susceptible to infection.

A fire blight infection occurred Wednesday, April 26, for orchards having rainfall that day. Symptoms from the April 15 and 16 fire blight infections should be appearing now. These may not have been significant events due to lack of bloom at that time. Growers will want to use Enviroweather’s Predictive Fire Blight Model to determine their risk for the last of bloom.

Pears are in petal fall. Fungicide applications for pear scab are ongoing. Growers should check their trees for fire blight from the April 15 and 16 infection periods. We are past bloom, so strep treatment should not be used for fire blight unless the orchard experiences hail or strong winds. Treatments for pear psylla are applied post-bloom and target rapid shoot growth and succulent leaves.

Small fruit

Grape shoot growth has begun in Concord, Niagara and very early varieties such as Marquette. Shoots are 3 to 4 inches long and flower clusters are exposed. These cold, wet conditions are excellent for phomopsis. Growers need to treat for this disease when the leaves fold back from the clusters.

Hybrids and vinifera grapes are at late bud swell to bud burst. Juice grapes are past the stage where grape flea beetles and climbing cutworm are a concern. As buds burst and shoot growth begins, grapes become very susceptible to freeze injury. See “How cold can grapes go?” by MSU Extension for more information.

Blueberries are blooming and new shoots are leafing out. Early blooming varieties are at full bloom. Later blooming varieties are at late pink bud to first bloom.

Elliot pink bud

Elliot blueberries are at pink bud and beginning to bloom. Image courtesy of Mark Longstroth, MSU Extension.

Mummy berry trumpets are up and growers should scout in areas where mummy berry has been a problem. Growers should apply fungicides to protect against mummy berry. Both shoot strikes and flower infections are possible now.

Cherry fruitworm adults were caught during the warm weather last week. If the cold, wet weather continues as long as expected, growers and consultants should reset their biofix when they catch moths again. Growers can use Enviroweather’s cherry fruitworm and cranberry fruitworm models to target their controls.

With flowers beginning to open, growers should be prepared to use their sprinkler irrigation systems to reduce damage to the flowers if a frost or freeze is predicted. See “Using Sprinklers to Protect Blueberries from Spring Freezes” by MSU Extension for more information.

Strawberry flower trusses are emerging the crown. Bloom has begun in some fields. Once strawberry flower buds above the ground, they can be hurt by temperatures in the 20s. Growers should have their sprinklers set up for freeze protection since the flower buds are vulnerable to freeze injury.

Straw covering strawberry field

Straw has been spread in many strawberry fields. Image courtesy of Mark Longstroth, MSU Extension.

Bramble leaves have unfolded on the floricanes. Primocanes are about 6 inches high. Scout for orange rust; spray to reduce its spread should be applied now.

Saskatoons are blooming

Upcoming meetings

Our next Monday fruit IPM meeting is Monday, May 8, at Fruit Acres Farms, 3452 Friday Rd, Coloma, MI, at 5 p.m. Two Michigan RUP applicator recertification credits are available at these meetings.

See also

Did you find this article useful?

You Might Also Be Interested In