MSU Extension Fruit & Nuts

Welcome to the fifth 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 

As has been the case for most of the season, we have seen warmer than normal temperatures and wetter than normal precipitation in most of the region for the last week. The growing degree day (GDD) gap is widening and we are even further ahead of previous years on GDD accumulation. Tree fruits are mostly done blooming aside from some lingering apple blossoms, blueberries are just past full bloom and entering petal fall, and raspberry bloom is just starting. Small fruit growers should still be keeping pollinator stewardship in the front of their mind. 

We are expecting scattered showers today, May 14, and a system developing overnight Thursday that could bring rain Friday and over the weekend. With those come increased risk for fungal infections like apple scab and bacterial infections like fire blight. Fire blight in particular can continue to pose a risk even in a year with crop loss because shoot blight can kill the entire tree. Read this 2020 article from George Sundin for fire blight management options. You can see an overview of disease risk on the RimPro interactive location chart. Make sure to check the models frequently as they change with weather forecasts. 

Local scouts in southeast Michigan have reported catches of codling moth males in the region. No visible apple scab has been reported yet for southeast Michigan, but scouts suggest that 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, also says 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 (MSU 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 restricted use pesticide (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 

Many apple cultivars are at fruit set. Lingering bloom can be seen around orchards in Romeo and Fenton. Apples observed at South Lyon were 7 millimeters (mm). We are still in primary scab season. RimPro is currently reporting a risk of a scab infection events on May 17. Some growers around the state are starting to put on sprays for chemical thinning. You can consult this 2022 article from MSU Extension on apple thinning strategies. 

Blueberries 

We are passing full bloom and moving into fruit set 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 has also been caught on the west side of the state. The critical temperature for damage for blueberries in full bloom is 27 degrees Fahrenheit. 

Brambles

We are seeing first flowers in summer red raspberries at sites in Fenton and Romeo. Watch out for orange rust and raspberry sawfly. 

Cherries 

We are seeing fruit set in both sweet and tart cherries in Fenton and Romeo ranging from 5-9 mm in tart cherries and 9-12 mm in sweet cherries. There is a risk of cherry leaf spot infection on May 17–18 and 21–22. 

Grapes 

We are seeing shoot growth up to 6 inches in Concord in Fenton, as well as inflorescences developing. We haven’t seen wild grape bloom, which is the biofix we use for controlling grape berry moth. 

Strawberries

We are seeing blooms in field strawberries in Fenton and Romeo as well as first fruit sets. Fungicides to control Botrytis gay 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 11 mm in diameter. Peaches seem to have been hit hardest by the frost event. The next chance to control brown rot will begin three weeks prior to harvest.  

Pears 

Pears observed in Fenton were 7 mm. Pear is susceptible to fire blight, so continue to watch models. 

Plums 

European plums in Fenton are 12 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 

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 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. Lorsban can no longer be used on bearing fruit trees. 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. The next control point comes at 100-200 GDD50 after biofix with the use of selective ovicidal products. 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: Catches remain low. We are past the control points for oriental fruit moth. 

Plum curculio: Plum curculio has been caught 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 leafroller: Flight was detected at the Trevor Nichols Research Center. 

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

San Jose scale: While we are not at the crawler stage, 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 Fennville, 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 for tarnished plant bug is closing. 

Disease conditions 

Apple scab: We are in primary scab season. RimPro is currently reporting a risk of a scab infection events on May 17 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 17–18 and 21–22. 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 18 and 21–22. 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 article “It’s that time of year for orange rust in brambles” 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 blueberrie,s 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. 

Powdery mildew and downy mildew of grape: Scouting should start early for these diseases. Read the article “Protecting young grape clusters from powdery and downy mildew” 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 over 12 hours of rain accumulating to 0.7 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 on Tuesday, May 14, with rain developing overnight Thursday into Friday with scattered showers continuing into the weekend. Temperatures will hit highs in the low 80s over the weekend with weekly lows in the mid-40s overnight Wednesday. 

In the medium term, we are looking at above normal precipitation through the end of May, with temperatures dropping to normal to below normal. 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 GDD accumulation for the season is ahead of the five-year average by 249 GDD at 42 F, 178 GDD at 45 F and 119 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.