MSU Extension Fruit & Nuts

Welcome to the eighth 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

Growers in southeast Michigan had a good opening weekend of strawberry U-picks. Upcoming cool temperatures should mean good harvest conditions.

We’ve seen an average of 1.3 inches of rain in the region over about 20 hours of rainfall for the last week 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. Tree fruit fruitlets are expanding and growers will have to consider hand thinning instead of chemical thinning. In brambles and blueberries, we are seeing fruit set with some continued bloom. Grapes are blooming and grape growers will be preparing their bloom sprays for fungal diseases.

We are expecting scattered showers and storms developing on Wednesday, June 5, which will usher in cool, cloudy conditions on Friday through the weekend with continued potential for showers. With these events come increased risk for fungal infections like secondary apple scab and powdery mildew. You can see you 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 numbers remaining high despite sprays. 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 Trevor Nichols Station in Fennville 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 30 millimeters (mm), well past the stage for chemical thinning, but 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. Michigan State University Extension educators in other parts of the state continue to catch primary scab spores in blocks that have had historic high pressure. Scab and fire blight strikes have been seen in Monroe County and other fire blight strikes have been seen in 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 blights and phomopsis. Cranberry fruitworm counts are increasing at the Trevor Nichols Research Center trap line and cherry fruit worm has been caught.

Brambles

We are seeing continued bloom alongside fruit set in summer red raspberries at sites in Fenton and Romeo while blackberries in warmer 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 pit hardening in cherries and fruit expansion in both sweet and tart cherries in Fenton and Romeo with fruit at 15 mm in tart cherries and 21 mm in sweet cherries. Both sweet and tart cherries are starting to show color. There is a risk of cherry leaf spot infection on June 6 and 8.

Grapes

Bloom has been seen in cold hardy wine grapes and Concord in the region. Growers will be preparing for fungicide sprays during bloom.

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 40 mm in diameter. Peach pit hardening has not yet started. The next chance to control brown rot will begin three weeks prior to harvest.

Pears

Pears observed in Fenton were at 26 mm.

Plums

Shiro plums observed in Romeo are 20 mm in diameter. The critical periods 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. In tree fruit, our insect concerns include codling moth and San Jose scale. In small fruit, grape berry moth, raspberry sawfly and cranberry fruitworm 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: 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 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. While chlorpyrifos is available for use this season, alternative 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 375 GDD₅₀ after biofix, which puts us in delayed spray timing (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: We will likely get the second generation of oriental fruit moth adults emerging in the next week. If control for the first generation wasn’t effective, sprays may be needed to control egglaying and larvae in the subsequent generation.

Plum curculio: Plum curculio remains active around the region, but they are on the decline. Watch especially in areas near woods or hedgerows. Egglaying may still be happening in cooler regions, but in warmer regions we are moving into the larval development stage.

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

Redbanded leafroller: Flight is 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 6 and 8 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 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 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 5, 8-9 and 12-13.

Powdery mildew and downy mildew of grape: Scouting should start early for these diseases. There is risk of powdery mildew infection June 5 and 11-13, and a risk of downy mildew infection June 5-6, 9 and 13 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 nearly 6.3 hours of rain accumulating to 0.2 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 and thunderstorms developing on Wednesday, June 5, and bringing in cool, windy and cloudy conditions through the weekend. Temperatures will hit highs in the mid- to upper 80s on Tuesday, with a cooldown into the 60s on Friday and then back into the 70s on the weekend. The weekly lows are expected to happen on Friday, hitting the 40s.

In the medium term, we are looking at below normal temperatures and precipitation through the next week followed by a return to warmer temperatures in mid-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 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.