MSU Extension Fruit & Nuts

Welcome to the ninth in-season fruit article update for Southeast Michigan for the 2024 season. Throughout the season these updates will include information about the weather in the past week and the upcoming week, a fruit-by-fruit guide to current conditions with appropriate pest and disease updates, and other relevant observations. 

General observations 

In the two weeks since the last update, strawberry harvest has come and gone. Many U-picks have started offering raspberries and both sweet and tart cherries are starting soon. Peaches, pear and apples can still be hand thinned. Blueberries and grapes continue to expand, with the earliest blueberry varieties in harvest. In blueberries we are seeing fruit coloration, but we’re not quite at harvest yet. Fruit set has been good on grapes. 

We’ve seen an average of 1.1 inch of rain in the region over about 13 hours of rainfall for the last two weeks, while continued warm temperatures and humidity have brought conditions favorable for disease. When using Enviroweather and other weather models, keep in mind that the weather station closest to you may have different topography or be in the path of weather events that pass by your location. The growing degree-day (GDD) gap is widening and we are even further ahead of previous years on growing degree day accumulation.  

There is a daily chance this week of scattered storms and showers. With these events come increased risk for fungal infections like secondary apple scab and powdery mildew. You can see an overview of disease risks on the RimPro interactive location chart. Make sure to check the models frequently as they change with weather forecasts. These weather conditions may make finding a suitable spray date tricky. 

Local scouts in southeast Michigan have caught both apple maggot and spotted wing drosophila in the region. They continue to report catches of codling moth males in the region, with numbers remaining high. Obliquebanded leafroller populations have also been observed above threshold at some orchards. The trap line report at the Trevor Nichols Research Center in Fennville, Michigan, has caught its first cherry fruit fly for the season, but we haven’t seen it in southeast Michigan yet. Scab and fire blight pressure remain low and powdery mildew seems to have been kept under control, but the risk of powdery mildew in tree fruit and grapes remains high. 

Next week Monday, June 24 is our last Southern Michigan virtual grower meeting. You can attend by registering on our event page. It is a good opportunity to ask questions and receive RUP credits. See the latest weekly fruit meetings for southern Michigan on MSU’s Kaltura Media Space (these may take a few days to upload after the Monday meetings). 

Fruit-by-fruit conditions 

Apples 

Apples in the region are generally in the 45–55 millimeter (mm) range. June drop has occurred in some orchards and hand-thinning can still be done. RimPro indicates that primary scab season is over with all spores being released, but secondary scab risk continues in places that have existing scab infections. Scab and fire blight strikes have been seen in Monroe County and other fire blight strikes have been seen blocks with historic pressure. 

Blueberries 

Fruit is sizing up and starting to show some color in blueberry plantings in Fenton. We are past the primary season for mummy berry and it’s time to pay attention to fruit rots—Anthracnose and Alternaria. Spotted wing drosophila has been caught in the region. See Michigan State University Extension’s collection of factsheets and videos on spotted wing Drosophila. 

Brambles 

Summer red raspberry U-picks have opened and blackberries are sizing up alongside some continued bloom. Spotted wing drosophila has been caught in the region. See Michigan State University Extension’s collection of factsheets and videos on spotted wing Drosophila. 

Cherries 

Some U-picks in the region are starting tart cherries and sweet cherry harvest will be starting soon. Read this article on bird management options for fruit growers. Spotted wing drosophila has been caught in the region. See Michigan State University Extension’s collection of factsheets and videos on spotted wing Drosophila. 

Grapes 

Fruit set in Concords, table grapes and cold hardy wine grapes has been good. Diseases of concern include powdery mildew, black rot and Phomopsis. On the insect side, tumid gallmaker is active this time of year. 

Strawberries 

Harvest is wrapping up. Renovation should begin as soon as you are done harvesting. This is an important step to ensure continued productivity next season. Read this 2023 article on strawberry renovation for additional information. 

Peaches and nectarines 

Peaches in Fenton and Romeo are in the stage where expansion levels off and the pit starts to harden. The next chance to control brown rot will begin three weeks prior to harvest.  

Pears 

Pears observed in Fenton were at 40 mm. 

Plums 

European plums observed in Romeo are 30 mm in length. The critical period for most fungal control is from petal fall to late June, but for brown rot specifically the critical times are during bloom and later on at fruit coloring. 

Insect conditions 

In tree fruit, our insect concerns include codling moth, spotted wing drosophila (for cherries) and apple maggot. In small fruit, grape berry moth and spotted wing drosophila are the biggest concerns. More in-depth information can be found by watching the latest weekly fruit meetings for southern Michigan on MSU’s Kaltura Media Space (these may take a few days to upload after the Monday meetings). 

Aphids: Scouts have seen light infestations of green apple aphids in recent weeks. While some aphids are best controlled during dormancy, woolly apple aphids are controlled during the season. Aphids can stunt shoot growth and pave the way for secondary fungal infections like sooty mold. 

Borer complex: With catches of dogwood borer and lesser peachtree borer in Fennville, it is time to review management options for borers. You can read about the current status of Lorsban in this 2024 update. See the 2024 Fruit Management Guide and the article “Timing trunk sprays for the borer complex in cherries.” While chlorpyrifos is available for use this season, alternatives materials may be used to manage borers as well. Assail is a recommended material for a trunk spray once adult borers are active. 

Cherry fruitworm: Scouts in the state have caught cherry fruitworm. 

Codling moth: Codling moth catches are up, with scouts in southeast Michigan indicating counts are high even after sprays. We are roughly at 600 GDD50 after biofix, which puts us in the period where additional larvicides can be applied if needed. You can track the codling moth model on Enviroweather. 

Cranberry fruitworm: Scouts in the state have caught cranberry fruitworm. 

Grape berry moth: Grape berry moth has been caught, but control is usually most effective in the second and third generations. See this early season grape berry moth management article for more information. 

Oriental fruit moth: We will likely get the second generation of oriental fruit moth adults emerging in the next week (I reported this a couple weeks ago, but it does not seem to have happened yet). If control for the first generation wasn’t effective, sprays may be needed to control egglaying and larvae in the subsequent generation. 

Pear psylla: This may need control throughout the season. 

Potato leafhopper: Populations can build quickly in June and peak in July. These can cause leaf margins to brown and are a bigger issue in young plantings. 

Raspberry sawfly: Adults emerge in the spring and lay eggs on leaves before bloom. Larvae feed on the leaves. 

San Jose scale: Crawler stage has been reported as continuing by scouts in southeast Michigan. At this control point, crawlers can be targeted with larvicidal sprays, but this will likely not be effective for much longer. See the 2024 Fruit Management Guide. 

We have moved past the control periods for rosy apple aphid, mites, green fruitworm, oriental fruit moth, tarnished plant bug, plum curculio and black stem borer. 

Disease conditions 

Apple scab: We are at the end of primary scab season and models are not predicting secondary infection risk in the next week. Scab pressure seems light this year. 

Black knot: There is still time to prune out and burn black knot in plums and sour cherries. Fungicides may be used for limited control to supplement pruning and sanitation efforts. 

Brown rot: This disease affects stone fruit and can proliferate during bloom. The next chance to control is about three weeks before harvest when fruits start to color. 

Cherry leaf spot: We expect risk of infection on June 22. See this 2013 article on cherry leaf spot management. 

Fire blight: Some fire blight strikes have been reported in orchards that have had fire blight in past years, but there do not appear to be many new infections this year. Read this 2020 article from George Sundin for fire blight management options. 

Grape black rot: There is potential conidi infection on June 22 in the region. See this 2014 article for grape black rot management options and consult the 2024 Fruit Management Guide... 

Orange rust: With our advanced growing degree days this year, we are hit the risk period for orange rust in brambles early. Read the linked article for control options. 

Peach leaf curl: Symptoms are starting to appear. Control needed to be done before bud break. The next chance to control it will be with fall sprays. 

Phomopsis: In blueberries, the Phomopsis fungus is active from bud swell until after harvest. 

Powdery mildew of apple and pear: You can start to include products labeled for powdery mildew in sprays starting at tight cluster. We are in a high-risk period for infection, especially June 21, 22 and 27. 

Powdery mildew and downy mildew of grape: Scouting should start early for these diseases. There is risk of powdery and downy mildew infections on June 19–20 and 25–26 in the region. Read the linked article for control options. 

While not a disease, nutrient deficiencies can leave plants more susceptible to disease. Now that the plants have leafed out, you can start to see some symptoms. They can be hard to definitively diagnose without nutrient testing, but this article from Eric Hanson is a handy guide to what nutrient deficiency symptoms look like.  

Seasonal weather update 

In the last two weeks, southeast Michigan has seen on average of over 13 hours of rain accumulating to 1.1 inch of precipitation. We are ahead of the five-year average in both time and amount of rainfall. 

In the short term, we are expecting variable conditions with scattered showers and thunderstorms possible every day. The early part of the week will be hot and humid, but early next week will bring dryer and cooler conditions. High temperatures this week will reach the mid-90s in the early part of the week with highs declining to the low 80s early next week. 

Laurel Harduar Morano with MSU’s College of Human Medicine says, “With a hot Michigan summer upon us, it is important to be mindful that hot weather can be dangerous while working outside. The heat produced by your body while working plus high outdoor temperatures makes it more likely for your body to overheat. To prevent overheating, do the following: drink plenty of fluids; take frequent breaks in the shade, and if possible, reschedule high energy tasks for earlier or later in the day.  

“Call 911 immediately if severe symptoms of overheating occur such as confusion, slurred speech, fainting, nausea/vomiting, rapid pulse, seizures, hot dry skin, or heavy sweating. Then, move the person to a cool place and help lower their temperature with a cool wet cloth and/or cool bath. Do not leave the person alone. Death can occur if the body does not cool down, so it is essential to have a plan before such symptoms occur.” 

In the medium term, we are looking at above-normal temperatures and near to above-normal precipitation through the next week. The long lead outlooks are still calling for warmer than normal conditions for the late spring and summer seasons with normal precipitation levels. 

Our regional average growing degree day accumulation for the season are ahead of the five-year average by 287 GDD at 42 F, 243 GDD at 45 F and 168 GDD at 50 F (see table below). This puts us at one to two weeks ahead of normal in most of the region. Read this Michigan State University Extension article to learn more about degree days: Understanding growing degree-days. 

Watch Jeff Andresen's biweekly agricultural weather forecast reports.  

More information and reports on normal weather conditions and departures from normal can be found on the NOAA Climate Prediction Center website, NOAA U.S. Climate Normals website, NOAA Climate Normals Quick Access Page (which may be searched by region), and Midwest Regional Climate Center website.