Southwest Michigan fruit update – June 12, 2018

Warmer, drier weather is ahead. Strawberry harvest is well underway.

Red apples on a shoot.
There are too many apple fruits on this shoot and they will need to be hand-thinned to insure good size at harvest. All photos by Mark Longstroth, MSU Extension.


Last week was cooler with highs in 70s. Highs rose into the 80s before the weekend. The weekend was stormy and rainy with heavy rains and flooding in some areas. Rain on Saturday and Sunday, June 9-10, were significant disease infection periods with long wetting periods that spanned the weekend. Measured rainfall totals for the weekend were generally 1 to 2 inches, but many areas received more and there was local flooding.

Soils are wet. Fields have standing water in low spots. Many growers have concerns about the rainfastness of the pesticide sprays.

This week will be warmer with highs rising to the 80s. Highs near 90 are forecast for the weekend. The chance of rain rises again on Friday, June 15. With the warmer than normal May, we are about a week ahead of our normal heat accumulation. The effect of Lake Michigan can be seen as the inland areas begin to accumulate heat faster than those located closer to the cool Lake.

Southwest Michigan GDD summary from March 1 – June 10, 2018


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

Fruit size increased noticeably over the past week due to the wet conditions. San Jose scale males have been flying since May 27 and crawlers should emerge approximately 375 GDD50 after biofix (May 27), which should be about June 17. This is the treatment window for crawler control.

Apricot fruit are 1 to 1.2 inches in diameter.

Peach and nectarine fruit are 28 to 30 millimeters in diameter. We expect pit hardening to begin next week. Hand-thinning is underway. Bacterial spot symptoms are becoming more common on susceptible varieties. Exposed fruit are prone to bacterial spot, rusty spot and peach scab infections. Bacterial spot protection with oxytetracycline is needed for warm, rainy periods.

We have been catching oriental fruit moth since May 7; our regional biofix is based on the Trevor Nichols Research Center trap line. There are fruit entries by first generation oriental fruit moth larvae. Ragged marks on peach fruit are probably due to tarnished plant bug feeding.

Estimated peach harvest dates are available on Michigan State University Enviroweather. Redhaven harvest is projected to begin about Aug. 1.

The first early-season sweet cherry harvest will start this weekend or next week. Montmorency tart cherries are still 12 millimeters in diameter. The fruit is starting to show straw color. The flesh will expand again as the fruit ripens. Some early harvest may start before the Fourth of July.

Cherry leaves are always susceptible to cherry leaf spot infection and need to be protected. We have not seen any cherry leaf spot symptoms yet. The weekend rains were significant cherry leaf spot infection periods. Sweet cherry fruit are always susceptible to brown rot infection and need to be protected.

Japanese plums are 20 to 22 millimeters and European plums are 17 millimeters in diameter at the Southwest Michigan Research and Extension Center. Fungicide treatment for black knot should continue until shoot growth stops. Some weather-related russeting is showing up on Japanese plum. Plum curculio will target plum fruit for egglaying.

Apple fruit range from 22-24 millimeters (Gala, Red and Golden Delicious) to 38 millimeters (Zestar) in diameter. Frost rings have been reported for some apple varieties, primarily Honeycrisp. We think these marks are due to low temperatures on April 29 and 30 when apple buds were at half-inch green to tight cluster.

Apple scab ascospore numbers have declined to low levels and the Enviroweather scab model predicts almost all the spores are mature and most have been released. Fire blight from blossom infections showed up two weeks ago on apples and pears in the southwest region. This likely traces back to a May 9 infection period. If there are only a few strikes on young trees, you may want to prune these out as quickly as possible. Cuts should be made at least 6 inches below any sign of the fire blight infection.

The regional bioix for codling moth was Monday, May 21. Egg hatch is underway (began June 2). Sprays should target hatching larvae. See “First generation codling moth management” from MSU Extension for more information.

Apple thinning will shift to thinning by hand. The crop looks generally decent despite a heavy drop due to hot weather. Crop loads vary greatly from orchard to orchard. Many only need light hand-thinning.

Pear fruit are 20 to 24 millimeters in diameter. Pear scab has been found on fruit. Fire blight from blossom strikes were found on Harrow Sweet pear, a variety with resistance. Pear psylla is the only major insect concern. The period after bloom during active shoot growth is a major psylla control window.

Small fruit

In grapes, Concord and Niagara are at or past full bloom. Vinifera and hybrid grapes are at mid-bloom. Black rot and phomopsis lesions can be found. The immediate post-bloom period is critical for controlling diseases on grape berries such as powdery mildew, downy mildew, phomopsis and black rot. Some growers have applied systemic fungicides in the dry periods between this last week’s rains.

Grape berry moth flight has peaked across southwest Michigan. Scout vineyards, looking for webbing in clusters. To determine if grape berry moth treatment is needed, sample 100 randomly selected clusters on the vineyard perimeter and another 100 clusters in the vineyard interior. If more than one in 10 clusters have a grape berry moth larva, treatment may be needed. Because the larvae are exposed in young clusters, a contact insecticide is a good choice if a post-bloom spray is needed. We will use May 27 as biofix for timing the second generation of grape berry moth. See “Using the MSU Enviroweather grape berry moth model in 2018” from MSU Extension for more information.

Blueberry fruit is sizing rapidly. With the wet conditions of the last month, there is water standing in many fields and spraying is difficult. Many growers are complaining of poor weed control. There is a Blueberry Pre-Harvest and Weed Control Update on Wednesday, June 20, from 7 to 9 p.m. south of Grand Junction, Michigan, in a blueberry field north of Silver Lake Road.

Overall, the crop looks good, but it is spotty in places. We are also seeing winter injury in some areas. We think this is due to very cold temperatures around New Year’s. We see shoots with lots of small fruit and few small leaves. Small fruit on shoots with no leaves will not size and will only stress the plants. These shoots should be removed.

Maintain fungicide protection on green fruit against anthracnose. Cherry fruitworm and cranberry fruitworm continues. There is a heavy flight of cranberry fruitworm. Egglaying is well underway, use contact insecticides to control these pests.

Strawberry harvest continues. Some berries ripened prematurely in the hot weather in May, but berries look better now as the cool weather has allowed them to size up. Some growers are complaining of small, misshapen fruit. Even with these problem, growers had trouble keeping up with demand. Leaf spot is common. Anthracnose is appearing.

misshapen strawberries TPB (1)

Small, misshapen fruit are the result from tarnished plant bug feeding on the young strawberries after bloom. The plant bug’s needle-like mouth kills the cells where it feeds and stops growth.

Bramble bloom is over. Black and red raspberries and blackberries have small, green berries. Primocane growth is very rapid.

Upcoming meetings

The next Monday fruit IPM meeting is June 18 at Fruit Acres Farms, 3452 Friday Rd, Coloma, MI at 5 p.m. Two Michigan RUP applicator recertification credits are available at these meetings.

Pre-register by June 13 for the first Clean Sweep for Southwest Michigan, scheduled for Wednesday, June 27, 2018. Clean Sweep allows pesticide users to safely dispose of unwanted pesticides.

 A Blueberry Pre Harvest and Weed Control Update is planned for Wednesday, June 20 from 7 to 9 p.m., south of Grand Junction in a blueberry field north of Silver Lake Road. The meeting will include updates and insect and disease control as well as a tour of an herbicide trial with standard and new pre-emergent herbicides applied in either fall or spring. Follow the link above for registration details.

 MSU Agriculture Innovation Day: Focus on Fruit and Vegetable Technologies is June 28 at the Southwest Michigan Research and Extension Center.

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