MSU Extension Fruit & Nuts

Welcome to the seventh 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

Many growers in the region are starting to pick strawberries, with many opening for U-pick this weekend. The crop is looking good this year.

The last week has largely seen increased precipitation along with above average temperatures, despite a few days with cooler temperatures. 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. Tree fruit fruitlets are expanding and many growers are still doing thinning applications while the threats of scan and fire blight wane. In brambles and blueberries, we are seeing fruit set with some continued bloom. Grapes are getting close to bloom and we have seen wild grape bloom in warmer parts of the state.

We are expecting scattered showers developing on Saturday, June 1, and lasting through the weekend into Monday. 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 continue to report catches of codling moth males in the region, with one scout commenting that the counts are very high. There hasn’t been much scab seen, but powdery mildew pressure is high this year. Fire blight has been seen in orchards where it has been a problem in the past. The trap line report at the Trevor Nichols Research Center in Fennville, Michigan,  also that insects in the cherry borer complex are continuing activity while leaf roller catches are down.

I encourage our growers to attend the weekly southern Michigan grower meetings virtually on Monday evenings 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 sizing up to 22-25 millimeters (mm) in Fenton and Romeo and as large as 30 mm in Britton. 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. Growers in cooler regions may still have time for sprays for chemical thinning. You can consult this 2022 article from Michigan State University Extension on apple thinning strategies.

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 blights and phomopsis. Cranberry fruitworm counts are increasing at the Trevor Nichols trap line.

Brambles

We are seeing continued fruit set in summer red raspberries at sites in Fenton and Romeo while blackberries in warmers parts of the region are in full bloom and starting fruit set. I’ve gotten reports of orange rust in the region. Watch out for orange rust and raspberry sawfly.

Cherries

We are seeing fruit expansion in both sweet and tart cherries in Fenton and Romeo with fruit at 15 mm in tart cherries and 18 mm in sweet cherries. Sweet cherries in warmer areas are starting to show color. There is a risk of cherry leaf spot infection on June 2, 5-6 and 8.

Grapes

Inflorescences continue to develop in table and wine grapes. I have yet to see wild grape bloom, which is the biofix we use for control of grape berry moth, but it has been seen in other parts of the state.

Strawberries

Harvest is starting. Be aware of preharvest intervals if you have to do any additional sprays.

Peaches and nectarines

Peaches in Fenton and Romeo are growing quickly, with some as high as 29 mm in diameter. The next chance to control brown rot will begin three weeks prior to harvest.

Pears

Pears observed in Fenton were at 24 mm.

Plums

European plums in Fenton are 18 mm in diameter. 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

Much of this week’s information is the same as last week’s. With many fruits at petal fall we are moving into first cover, but if your crops are still blooming remember to prioritize pollinator protection. In tree fruit our insect concerns include codling moth and San Jose scale. In small fruit, grape berry moth, raspberry sawfly, cranberry fruit worm are of concern. 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: 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 American plum 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” for more information. 

Codling moth: Codling moth catches are up, with scouts indicating that it is a heavy year. We are roughly at 300 GDD₅₀ after biofix, so there may be time for egg hatch larvicidal sprays in cooler areas (normally at 250 GDD₅₀ after biofix) with delayed spray timing occurring around 350 GDD₅₀ after biofix. 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.

Oriental fruit moth: Catches remain low. We are past the control points for oriental fruit moth.

Plum curculio: Plum curculio remains active around the region. In warm conditions like the ones we are experiencing, adults move from overwintering sites into orchards. Watch especially in areas near woods or hedgerows. Products that as oviposition deterrents and feeding killers can be used in apples and cherries at this point, while those that are just feeding killers are no longer recommended.

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

Redbanded leaf roller: Flight are decreasing.

Rose chafer: These emerge from soil in late May to early June. Treatment is only necessary with large populations.

San Jose scale: Crawler stage has been reported by scouts in southeast Michigan. At this control point, crawlers can be targeted with larvicidal sprays. See the 2024 Fruit Management Guide.

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

Disease conditions

Apple scab: We are at the end of primary scab season. RimPro is currently reporting a risk of secondary scab infection events on June 2, 5 and 6 in the region. 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 moderate risk of infection on June 2, 5-6 and 8. 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. Monitor RimPro, Enviroweather and integrated pest management updates for spray timing. Read this 2020 article from George Sundin for fire blight management options.

Grape black rot: There is potential conidi infection on June 2, 5 and 6 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 hitting 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 2, 4 and 5.

Powdery mildew and downy mildew of grape: Scouting should start early for these diseases. There is risk of downy mildew infection on June 2, 5 and 6 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 week, southeast Michigan has seen on average of nearly 22 hours of rain accumulating to 1.3 inches of precipitation. We are ahead of the five-year average in both time and amount of rainfall.

In the short term, we are expecting scattered showers developing on Saturday and lasting through the weekend into Monday. Temperatures will hit highs in the mid-80s next week with the weekly lows happening Friday, hitting the 40s.

In the medium-term, we are looking at above normal precipitation and temperatures into early June. 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 280 GDD at 42 F, 236 GDD at 45 F and 162 GDD at 50 F (see table below). This puts us 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.