Southwest Michigan fruit update – Aug. 8, 2017

Peach and blueberry harvest is moving quickly.

Heavy bloom, good pollination and irrigation leads to good fruit set and size in blueberries. Photo by Mark Longstroth, MSU Extension.

Heavy bloom, good pollination and irrigation leads to good fruit set and size in blueberries. Photo by Mark Longstroth, MSU Extension.


Last week began warm, with highs in the mid-80s and lows near 60. A cold front moved through the region Thursday night, Aug. 3, and Friday saw widespread lake effect showers. This was the first significant rain in the region since July 13. Rainfall was very uneven. Some areas received about a third of an inch and other received over 1 inch. The average across sites was just over two-thirds of an inch. Comparing this season’s rain across southwest Michigan shows an average of almost 13 inches, many sites receiving 10 to 13 inches and some sites 15 to 18 inches.

Last week’s potential evapotranspiration was about 1 inch of water and for a season total of over 21 inches since April 1. This was due to the cloudy cool conditions most of the week. This week will be warmer with highs rising into the 80s early in the week and then falling towards the end of the week. There is a chance of showers Thursday and Friday, Aug. 10 and 11. We are about a week ahead of normal. Crop harvests seem to be about two weeks ahead of normal.

Southwest Michigan GDD summary from Jan. 1 – Aug. 6, 2017


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMRC)




Lawton (Lawton)




Fennville (TNRC)




Average for the SW region




Ave from March 1




Accumulation last week




Tree fruit

Japanese beetles are generally scarce, but they are a problem in some locations. San Jose scale catch rose sharply two weeks ago at the Trevor Nichols Research Center. This rise signals the start of the third generation. Any site showing red spots on fruit or limbs this season should be treating for crawlers 375 growing degree-days (GDD) base 51 F from July 31, or about Aug. 10. Growers can review the insect trap catches at Trevor Nichols Research Center.

Brown marmorated stink bugs in the past few years have caused problems in orchards starting in mid- to late August. Currently, only the non-flying nymphs are being caught. Stone fruit trees continue to shed older leaves due to earlier disease and drought stress. Leaf samples for foliar tissue analysis should be collected from mid-July to mid-August. Tissue samples should be sent to A&L Labs.

Peach growers are reporting that harvest is moving rapidly, with harvests of PF17 and Allstar to start soon in some sandy sites. Quality continues to be good. Some growers are applying Retain to part of their acreage to stretch out the harvests. Retain should be applied seven to 10 days before anticipated harvest. Fruit speckles due to bacterial spot can be seen where infected leaves are nearby. To increase fruit color, do light summer pruning one to two weeks before harvest on varieties needing more color.

Oriental fruit moth trap catch continues to be significant in some orchards. We are in the third generation oriental fruit moth flight. Stink bug and tarnished plant bug damage can increase fruit susceptibility to brown rot. As fruit colors, the need for brown rot protection increases. Rotate fungicide classes used for brown rot control to avoid resistance problems.

leaf drop in peaches

Leaves are being shed in peaches due to bacterial spot and other stresses such as drought. Photo by Bill Shane, MSU Extension.

In cherries, yellow leaves are common. Cherry leaf spot is a serious problem in some orchards. Other stresses such as drought can cause yellowing and leaf drop. Chlorothalonil is used after harvest to help suppress cherry leaf spot with low risk of resistance buildup by the fungus.

Plum harvest continues with Redheart, Castleton and Rubyqueen. Thicker skinned European plums are a less favorable host for spotted wing Drosophila (SWD), but you should still protect fruit from SWD. Ripening plums need to be protected from brown rot. Apple maggot also attacks plums, however SWD sprays should also control this pest.

Apple development is continuing with Zestar and Rubymac now testing three (five is considered mature) for starch conversion on the Cornell University scale. Zestar harvest appears to be about one week early, based on blush and sugar development. Fungicides to reduce sooty blotch and flyspeck should be reapplied as rains wash off fungicide coverage.

Oriental fruit moth have been up and down, but the third generation flight should be flying now. Codling moth trap catches are generally low. Obliquebanded leafroller larvae are feeding on foliage and fruit. Apple maggot is a summer apple pest, which emerges after a rain and attacks apples. After the rainy weekend, we can expect a good emergence of this pest. Apple maggot trap catch numbers continue to be relatively high. Be sure the insecticides used will control all the insects attacking fruit. Woolly apple aphid aerial colonies are becoming easier to find.

Pear (Bartlett and Harrow Sweet) fruit range from 2.25 to 2.5 inches in diameter. A minimal spray program will help to hold sooty blotch and fly speck in check. Pear psylla levels seem low.

Small fruit

Early grape varieties should begin veraison soon. The beginning of third generation grape berry moth egglaying was Aug. 5. Therefore, this week is the most important treatment window of the year for grape berry moth. Catch of SWD is higher this year than previous years. It is likely that SWD will be a problem after veraison in wine grapes. Hang traps for SWD and treat after veraison if necessary.

Symptoms of powdery mildew are present in some vineyards. Growers will be treating for this disease. We are entering the later part of the summer and heavy morning dews are common. Downy mildew can spread quickly under these conditions and growers need to be ahead of this disease. Grape leafhoppers and potato leafhoppers are not a problem in most vineyards this year. Japanese beetle numbers are somewhat increasing.

powdery mildew

Powdery mildew can be found on grape berries. Photo by Mark Longstroth, MSU Extension.

Blueberry harvest is into its final weeks in Van Buren County. Growers are picking Liberty, Elliott and other late varieties, as well as finishing Jersey and other mid-season varieties. The season will be ending a week or two early. Harvest will continue in the northern growing areas for several more weeks. Harvest labor has been a significant problem. Fruit quality is variable as growers struggle to remove ripe fruit quickly.

SWD and anthracnose fruit rot have been significant problems. SWD numbers are very high. Tight spray schedules are needed to control SWD. Protecting ripe fruit is very hard. Even with excellent insecticide programs, the longer ripe fruit stays in the field the more likely it is to be attacked by SWD. Tight harvest schedules reduce the time ripe berries are exposed to SWD.

The effect of the May 8 freeze and cold windy weather during bloom have been easy to see in some locations. In some fields, many very small fruit is evident. These fruit were not pollinated and did not fall off the bush earlier in the season. This fruit will never size.

Bramble harvest continues. We are in a gap between summer red raspberries, which are ending, and fall red raspberries, which will begin in a week or two. Blackberry harvest is underway. SWD continues to be a real problem in raspberries and blackberries one of their favorite hosts. For some growers, it has caused an early end to the season.

SWD are attracted to the fruit as it changes color and begins to ripen. Michigan State University Extension advises protecting fruit from SWD—see the MSU recommendations for SWD control in brambles. One of the best defenses is to pick as often as you can and remove ripe fruit as quickly as possible. After harvest, cool the fruit as quickly as possible.

Strawberries are showing good growth and most fields are producing runners. Protect renovated plantings from potato leafhopper, which stunts plant growth. Irrigate renovated strawberry fields to get good growth for next year.

Upcoming meetings

An open house at the Southwest Michigan Research and Extension Center is Tuesday, Aug. 15, from 1 to 4:30 p.m. Join us for project tours of vegetable, tree fruit, bramble and blueberry research. There is no charge for this meeting. To allow us to plan, please pre-register.

The Michigan Grape Society is hosting its next Grape Grower Social Aug. 16 at 3 p.m. at the Round Barn Winery. The event includes an educational segment by MSU Entomology. Registration is $15 and includes a light supper and wine.

A Research field day at the Trevor Nichols Research Center is Tuesday, Sept. 26, from 1 to 4 p.m. The field day will focus on insect and disease research and efficacy trials.

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