MSU Extension Fruit & Nuts

Welcome to the sixth 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.

Note, this update may be posted later than usual due to upgrades to the Michigan State University Extension site.

General observations

As has been the case for most of the season, we have seen warmer than normal temperatures, though precipitation was generally down in the region for the last week. Precipitation has been patchy, with some parts of the region getting more rain than normal and others staying quite dry. When using Michigan State University 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. I have had reports of some growers experiencing hail events in the last week, and as there is potential for more severe weather this week, I am again sharing this article: How should fruit growers respond to hail and severe storms?

The growing degree-day 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 applying thinning applications while the threats of scan and fire blight wane. In brambles and blueberries, we ae 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 and storms today (May 21) and developing again on Friday (May 24) and lasting through the weekend. With these events come an 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. No visible apple scab or fire blight has been reported yet for southeast Michigan, but powdery mildew may pose a particular challenge this year for apple growers. The trap line report at the Trevor Nichols Research Center in Fennville, Michigan,chigan, also says that insects in the cherry borer complex are starting to become active.

Many of you will have already done spring weed control, but if not, this 2020 Michigan State University Extension article on spring herbicide applications lists some available options.

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 around 10-12 millimeters (mm) in the Fenton area and as large as 26 mm in Britton. RimPro indicates that primary scab season is just about done, but secondary scab risk continues in places that have existing scab infections. Many growers around the state are putting on sprays for chemical thinning. You can consult this 2022 article from MSU Extension on apple thinning strategies.

Blueberries

We are primarily at fruit set in blueberry plantings in Fenton with a few lingering blossoms. We are past the primary season for mummy berry and it’s time to pay attention to blights and phomopsis. Cranberry fruitworm has also been caught on the west side of the state.

Brambles

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

Cherries

We are seeing fruit expansion in both sweet and tart cherries in Fenton and Romeo ranging from 11-13 mm in tart cherries and 12-15 mm in sweet cherries. There is a risk of cherry leaf spot infection on May 21 and 25-26.

Grapes

We are seeing shoot growth up to 12 inches in Concord in Fenton while inflorescences continue to develop. We haven’t seen wild grape bloom, which is the biofix we use for control of grape berry moth, but we expect to see it in the next week.

Strawberries

We are fruit set and growth in field strawberries in Fenton and Romeo as well as continued bloom. Fungicides to control Botrytis grey mold may be necessary soon. Twospotted spider mites have been observed in strawberries by scouts in the region.

Peaches and nectarines

Peaches in Fenton and Romeo are around 12-14 mm in diameter. Peaches seem to have been hit hardest by the frost event, but many seem to be bouncing back. The next chance to control brown rot will begin three weeks prior to harvest.

Pears

Pears observed in Fenton were at 16 mm.

Plums

European plums in Fenton are 14 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, tarnished plant bug, San Jose scale, codling moth and obliquebanded leafroller. 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: While some aphids are best controlled during dormancy, woolly apple aphids are controlled during the season. See linked articles for more information. 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. Last week I mentioned that Lorsban can no longer be used on bearing fruit trees, but this change has been delayed. You can read more information 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: First codling moths have been caught around southeast Michigan in the last week. We are currently at the control point (100-200 GDD₅₀ after biofix) to use selective ovicidal products. You can track the codling moth model on Enviroweather.

Cranberry fruitworm: Scouts in the state have caught cranberry fruitworm. See the linked fact sheet for more information.

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 have 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 detected at Fennville station.

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 in Fennville on the west side of the state, but scouts in southeast Michigan expect crawlers in about a week. Products like Movento that induce a systemic response in plants need time to work and can be applied ahead of the crawler stage. San Jose scale males have been caught in the region, which is an indicator that the crawler stage is coming soon.

Tarnished plant bug: You should avoid mowing until after bloom when you can use insecticides because mowing can cause the tarnished plant bug to move from the orchard floor to feed on flowers and developing fruit.

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

Disease conditions

Apple scab: We are at the end of primary scab season. RimPro is currently reporting a risk of secondary scan infection events on May 21 and 25-26 in the region. Early control of scab is important for reducing secondary scab infections that can affect fruit.

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 May 21 and 25-26. See this 2013 article on cherry leaf spot management.

Fire blight: 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 May 21 and 25. See this 2014 article for grape black rot management options and consult E-154.

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.

Powdery mildew and downy mildew of grape: Scouting should start early for these diseases. 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 6 hours of rain accumulating to 0.5 inches of precipitation and 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 storms on Tuesday. Wednesday through Friday will be cooler and drier, but the weekend will bring more scattered showers. Temperatures will hit highs in the low 80s over the weekend with weekly lows in the upper-40s.

In the medium term, we are looking at above normal precipitation and temperatures through the end of May, with temperatures and precipitation dropping to normal in 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 (GDD) accumulation for the season are ahead of the five-year average by 264 GDD at 42 F, 222 GDD at 45 F and 151 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.