MSU Extension Fruit & Nuts

Welcome to the first 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

The warm and wet weather we have had so far this season has pushed many of our fruit crops along in bud development. We are seeing bloom in peaches and plums and getting close in sweet cherries. With temperatures this weekend dropping close to some critical temperatures, be watchful for radiative frost events. There is some risk for Saturday morning, April 20, but the greatest risk will come overnight Saturday and overnight Sunday. It may help to review this 2020 Michigan State University Extension (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.

The continued chance of rain means that disease risk will still be present. Based on the RimPro models at the Romeo station, for which you can see you an overview on the RimPro interactive location chart, we are expecting the potential for apple scab infection from April 18 – 20. The risk of economic loss due to scab is highest early in the season because it is a disease that will recur and intensify with successive generations.

The trap line monitoring has started at the Trevor Nichols Research Center in Fennville, Michigan,chigan. Moths have started flying, including green fruitworm, redbanded leafroller, spotted tentiform leafminer and oriental fruit moth. For southeast Michigan specific data, I will be sharing information passed along to me from local scouts who set traps up this week. I will be setting out some traps in the region the next few weeks to monitor pests for entomology research projects on campus and invasive pests.

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

Most apples in the region are between tight cluster and pink. First blossoms in Manchurian Crab have been reported in apples near our warmest Enviroweather station at Deerfield. We are in primary scab season. RimPro is currently reporting a risk of a scab infection event from April 18 – 20.

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. Given the chance of rain this week, you may need to add a sticker type spray adjuvant that will make the spray less prone to wash off. Critical temperatures for apples at tight cluster are 27 degrees Fahrenheit for 10% kill and 21 F for 90% kill. At the full pink stage, critical temperatures are 28 F for 10% kill and 25 F for 90% kill.

Blueberries

We are seeing tight cluster to early pink bud in blueberry plantings in Fenton. 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 at prebloom so there is still time for delayed dormant sprays. See the Michigan Fruit Management Guide (E-154) for more information.

Cherries

We are seeing white in sweet cherries and open cluster in tart cherries in Fenton. Copper sprays aren’t recommended past the prebloom stage because of phytotoxicity. Expansion of first bract leaves (beginning of risk period for cherry leaf spot) is expected at 250 growing degree days (GDD) base 42 after Jan. 1, which is the average accumulation at our sites in the region as of April 15 (see GDD table in the weather update section).

The critical temperatures for sweet cherries at first white are 27 F for 10% kill and 24 F for 90% kill, and for 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

No movement yet in many locations, but Marquette in Ray Township is starting to move. Dormant sprays are still effective.

Strawberries

We are seeing some foliage emerge in field strawberries in Fenton. Growers are starting to remove straw. Early season fungicides should focus on controlling leafspot.

Peaches and nectarines

Peaches in Fenton are at first bloom. Brown rot control is usually done during bloom and is especially important in orchards that have been affected in the past. At first bloom, the critical temperatures are 26 F for 10% kill and 21 F for 90% kill.

Pears

Pears in Fenton are at the tight cluster stage. Delayed dormant sprays for pear psylla can be applied at reduced rates as we get closer to the white stage, but the window is closing quickly because oils can often damage new plant tissue. At tight cluster, the critical temperatures for pear are 24 F for 10% kill and 15 F for 90% kill.

Plums

Early plums, like Methley, are at full bloom in Fenton with others close behind. 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

In tree fruit, our insect concerns include mites, scale, rosy apple aphid, tarnished plant bug, green fruit worm, 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: Main control is to target emerging females as they search for new sites to deposit eggs, which should be in the coming weeks.

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.

Pear psylla: We are at the end of the window for early control with dormant oil in warmer areas. After this point, control requires reducing vegetative flushes and hand-removing suckers.

Redbanded leafroller: Flight detected at Fennville station.

Rosy apple aphid: Check for colonies in fruit clusters when we get to the pink stage. If necessary, use a prebloom insecticide for control.

San Jose scale: We are at the end of the window for early season dormant oil applications in warmer areas. The next opportunity to control them is during their crawler stage around the second cover in apples.

Spotted tentiform leafminer: Flight detected at Fennville station.

Tarnished plant bug: Pyrethroids are the most effective pink stage spray.

Disease conditions

Apple scab: We are in primary scab season. RimPro is currently reporting a risk of a scab infection event from April 18 – 20 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.

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 nearly 30 hours of rain accumulating to 1.2 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 showers and thunderstorms developing Wednesday, April 17, including the possibility of strong storms. Thursday will be cooler with potential for rain overnight followed by dry and cool conditions from Friday into the weekend.

We will have frost and freezing temperatures possible over the weekend, with risk for frost events on Saturday, Sunday and Monday 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 both the mean temperatures and precipitation being near normal for about a week followed by above normal temperatures and precipitation in late April. The long lead outlooks are still calling for warmer and wetter than normal conditions for the late spring and summer seasons.

Our regional average growing degree day accumulation for the season is ahead of the five-year average by 77 GDD at 42 F, 55 GDD at 45 F and 28 GDD at 50 F (see table below). 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.