MSU Extension Fruit & Nuts

Welcome to the second 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 saw a few frosty mornings. Overnight from April 20-21, we saw a low of 28.9 degrees Fahrenheit at the Hudson Enviroweather station in Lenawee County and the entire southeast region dipped below freezing. The Hudson Enviroweather station was even lower overnight from April 21-22, getting to 27.8 F. These temperatures were low enough to cause some minor damage in flowering fruit trees. 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.

Despite overnight lows, the last week has been above normal in temperature and we are seeing bloom in many stone fruits and early apple cultivars. 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 continued unstable weather conditions, which can include severe storms, hail and frost events (see the article “How should fruit growers respond to hail and severe storms?”). Like last week, you should also review this 2020 Michigan State University (MSU) Extension article on what to do if a freeze is coming. You can also refer to the picture table of fruit freeze damage thresholds.

Many growers were spraying fungicides on stone fruit yesterday, April 22, to control diseases like brown rot, peach leaf curl, cherry leaf spot and powdery mildew. Based on the RimPro models at the Romeo station, for which you can see you an overview on the RimPro interactive location chart, we expecting some risk for scab tomorrow (April 24) and Saturday, and fire blight next week. We are expecting highly variable weather conditions in the coming week and the models could change. Just between yesterday and today the model changed from no scab risk to actionable scab risk, so make sure to check frequently.

Local scouts in southeast Michigan have reported catches of black stem borer, oriental fruit moth and woolly apple aphids as well. The trap line report at the Trevor Nichols Research Center in Fennville, Michigan, indicates that moths have started flying, including green fruitworm, redbanded leafroller, spotted tentiform leafminer and oriental fruit moth.

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 restricted use pesticide 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

Early apple cultivars like Zestar and Liberty are starting to bloom at the MSU Tollgate Farm in Novi, Michigan. Around the region, many crabs are in bloom and most other cultivars are right behind at the pink stage. We are in primary scab season. RimPro is currently reporting a risk of a scab infection event on April 24 and 27. Powdery mildew season starts with half-inch green and rust season starts around pink, so you may need to use a product with a broader effect. Critical temperatures for apples from full pink to bloom are 28 F for 10% kill and 25 F for 90% kill.

Blueberries

We are at early pink bud in blueberry plantings in Fenton, Michigan. 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. The critical temperature for damage for blueberries at tight cluster is 20-23 F and for early pink bud is 23-25 F.

Brambles

We are seeing growth in both red and black raspberries at sites in Dexter and Fenton. We are still in prebloom, so there is still time for delayed dormant sprays. See E-154 for more information.

Cherries

We are seeing bloom in sweet cherries and first white in tart cherries in Fenton and Romeo. Copper sprays aren’t recommended past the pre-bloom stage because of phytotoxicity. 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 full bud swell in Marquette in Ray Township, Michigan, and first bud swell in Concord in Fenton. Dormant sprays are still effective.

Strawberries

We are seeing continued foliage growth in field strawberries in Fenton and Romeo. Growers continue to remove straw. Early season fungicides should focus on controlling leaf spot.

Peaches and nectarines

Peaches in Fenton and Romeo range from first bloom to full bloom. 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 in Fenton are at full bloom. Pears are susceptible to fire blight, so continue watching models. At full bloom, the critical temperatures for pears are 28 F for 10% kill and 24 F for 90% kill.

Plums

Stanley and Shiro are at full bloom in Fenton with Methley moving into petal fall. 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 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. The critical temperatures for European plums in full bloom are 28 F for 10% kill and 23 F for 90% kill.

Insect conditions

In tree fruit, our insect concerns include tarnished plant bug, green fruitworm, oriental fruit moth, obliquebanded leafroller and black stem borer. 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: The main control is to target emerging females as they search for new sites to deposit eggs, which starts around 100 GDD₅₀. Black stem borer was caught by a scout in Deerfield, Michigan, last week.

Green fruit worm: Flight as detected at the Fennville station. Green fruitworm can be controlled with insecticides post-bloom.

Oriental fruit moth: There is still a brief window to implement mating disruption, but the next major control point comes at egg deposition with the use of an ovicidal product 100-150 GDD₄₅.

Redbanded leaf roller: Flight detected at Fennville station.

Spotted tentiform leafminer: Flight detected at Fennville station.

Tarnished plant bug: Avoid mowing until after bloom when you can use insecticides because mowing can cause 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.

Disease conditions

Apple scab: We are in primary scab season. RimPro is currently reporting a risk of a scab infection event for April 24 and 27 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.

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 integrated pest management updates for spray timing.

Mummy berry: Southwest Michigan scouts report apothecia showing up. See Michigan Blueberry Facts: Mummy Berry (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

In the last week, southeast Michigan has seen on average of over 10 hours of rain accumulating to 0.8 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 showers and thunderstorms to develop on Tuesday, April 23, including the possibility of strong storms. There is potential for continued showers and even snow flurries overnight. Friday into Saturday will bring warmer weather and rain.

We will have frost and freezing temperatures possible Wednesday and Thursday mornings. It may help to review this 2020 MSU Extension article on what to do if a freeze is coming. You can also refer to the picture table of fruit freeze damage thresholds.

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 (GDD) accumulation for the season is ahead of the five-year average by 102 GDD at 42 F, 74 GDD at 45 F and 28 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.