MSU Extension Fruit & Nuts

Welcome to the third 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 last week we unfortunately experienced multiple days with overnight temperatures below freezing. In particular overnight from April 24-25 we saw lows in the entire region that can cause damage to flowering fruit crops. For information on assessing frost damage please read the Michigan State University Extension article “Assessing frost and freeze damage to flowers and buds of fruit trees.” You can check the overnight temperatures at your nearest station on Enviroweather and refer to the picture table of fruit freeze damage thresholds. It is not always immediately apparent what the extent of damage is after a frost event. I expect that our growers will continue to assess what amount of crop has been lost and what is still viable in the coming week.

Despite overnight lows, the last week has been above normal in temperature and we continue to see bloom in apples, cherries, and blueberries. Read this article on pollinator stewardship, which is always of paramount concern during bloom. The primary message is not to spray products that could be harmful to pollinators during bloom when pollinators are active.

We are expecting a few rain events this week, and 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. Using programs implementing Apogee and Actigard or antibiotic sprays can continue to protect your orchard. You can see you a 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 black stem borer, oriental fruit moth, woolly apple aphids, green fruit worm, oblique banded leafrollers, and red banded leafrollers. The trap line report at Trevor Nichols Research Center in Fennville indicates that green fruit worm catches are decreasing while oriental fruit moth catches are increasing. There were new catches of grape berry moth and cranberry fruitworm, but no codling moth or American plum borer catches yet.

Many of you will have already done spring weed control, but if not this 2020 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 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 in full bloom at the MSU Tollgate Farm in Novi. Around the region many cultivars were in bloom during the frost and there was considerable damage. Some later cultivars, like Northern Spy, may have fared better because of their less advanced phenological stage. We are in primary scab season. RimPro is currently reporting a risk of a scab infection events on April 30 and May 4. With warm temperatures forecast during bloom there is also a high risk for fire blight infections. Read this 2020 article from George Sundin for fire blight management options. Critical temperatures for apples from full pink to bloom are 28 F for 10% kill and 25 F for 90% kill.

Blueberries

We are late pink bud to first bloom in blueberry plantings in Fenton. Some damage has been observed on blueberries, but it does not appear to be extensive. This is the primary risk period for mummy berry and it is time to start paying attention to phomopsis. FRAC 3 fungicides are reported to be efficacious for both mummy berry and phomopsis. Cranberry fruit worm has also been caught on the west side of the state. The critical temperature for damage for blueberries at late pink bud is 24-27 F and for full bloom is 27 F.

Brambles

We are seeing growth in both red and black raspberries at sites in Plymouth and Fenton.

Cherries

We are post bloom in sweet cherries and at full bloom in tart cherries in Fenton. Sometimes the shuck can provide some protection from frost if it is still on, but damage was observed in both sweet and tart cherries. There is a moderate risk of cherry leaf spot infection on April 30, May 4, and May 7. The critical temperatures for sweet cherries at full bloom are 28 F for 10% kill and 25 F for 90% kill. The critical temperatures for tart cherries from open cluster to full bloom are 28 F for 10% kill and 24°F for 90% kill.

Grapes

We are seeing first leaf in ‘Marquette’ in Ray Township and full bud swell in ‘Concord’ in Fenton. Warmer areas with more leaves may have seen some frost damage, but grapes in the southeast largely pulled through the frost without issue.

Strawberries

We are seeing continued crown and flower formation in field strawberries in Fenton. Early season fungicides should focus on controlling leaf spot.

Peaches and nectarines

Peaches in Fenton are at petal fall. Sometimes the shuck can provide some protection from frost if it is still on, but damage was observed in peaches. Peach can be difficult to assess for damage immediately after a frost. Brown rot control is usually done during bloom and is especially important in orchards that have been affected in the past. At full bloom the critical temperatures are 27 F for 10% kill and 24 F for 90% kill.

Pears

Pears observed in Fenton were at petal fall. Frost damage was seen mixed in with healthy flowers. Pear is susceptible to fire blight, so continue to watch models. At petal fall the critical temperatures for pear are 28 F for 10% kill and 24 F for 90% kill.

Plums

European plums in Fenton are petal fall. Sometimes the shuck can provide some protection from frost if it is still on, but damage was observed. Prune out black knot and dispose of the knots by burning or removing from the orchard. Sanitation is an important step in managing this disease. 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. The critical temperatures for European plums in full bloom are 28 F for 10% kill and 23 F for 90% kill.

Insect conditions

With many fruits at petal fall we are looking at first cover, but if your trees are still blooming remember to prioritize pollinator protection. In tree fruit our insect concerns include codling moth, tarnished plant bug, green fruitworm, oriental fruit moth, obliquebanded leafroller and black stem borer. In small fruit grape berry moth 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).

Black stem borer: Main control is to target emerging females as they search for new sites to deposit eggs, which starts around 100 GDD₅₀. We are around the peak time for this emergence and regional scouts continue to catch them.

Codling moth: No codling moths have been caught yet, but we expect biofix to happen soon. There is still time to use mating disruption. The next control point comes at 100-200 GDD₅₀ after biofix with the use of selective ovicidal products.

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

Green fruitworm: Catches are still being reported, but are on the decline. These can be controlled with insecticides post-bloom.

Oriental fruit moth: We are approaching the end of the egg-deposition control point with the use of ovicidal products from 100-150 GDD₄₅. The next control point comes up quickly from 170-195 GDD₄₅ at 10-15% egg hatch.

Plum curculio: 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 work primarily as feeding killers can be applied in first cover, while those that also work as oviposition deterrents should be used later in the season.

Redbanded leafroller: Flight detected at Fennville station.

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.

Spotted tentiform leafminer: Flight detected at Fennville station.

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, and mites and the control window for green fruit worm and black stem borer is closing.

Disease conditions

Apple scab: We are in primary scab season. RimPro is currently reporting a risk of a scab infection events on April 30 and May 4 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. Fungicides may be necessary to control if bloom is during a warm period, especially in orchards that have had brown rot presence in previous seasons.

Cherry leaf spot: We expect moderate risk of infection April 30, May 4, May 7. See this 2013 article on cherry leaf spot management.

Fire blight: We expect high risk for fire blight this week. Growers are applying antibiotic sprays to control fire blight. If you have had fire blight in the last few years you may have applied a preventive copper spray, but copper can be phytotoxic to young leaves and should not be applied once leaves are present. Control is primarily done during apple and pear bloom. Monitor RimPro, Enviroweather, and IPM updates for spray timing. Read this 2020 article from George Sundin for fire blight management options.

Grape black rot: There is potential conidi infection April 30, May 4, May 7. See this 2014 article for grape black rot management options and consult E-154.

Mummy berry: Southwest Michigan scouts report apothecia showing up. See the linked document E2846 for control methods.

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.

Seasonal weather update

See above for a table of low temperatures overnight April 24-25, 2024.

In the last week, southeast Michigan has seen on average of over 14 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 fair conditions on Tuesday and Wednesday with showers developing on Thursday May 2 and continuing into the weekend. Temperatures will hit highs in the upper 70s over the weekend while lows are expected in the 40s.

In the medium term we are looking at above normal mean temperatures and precipitation totals. 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 140 GDD at 42 F, 109 GDD at 45 F and 63 GDD at 50 F (see table below). This puts us at 1 to 2 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.