MSU Extension Fruit & Nuts

Welcome to the fifth in-season fruit article update for southeast Michigan for the 2023 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 milder weather the last week has pushed apples into bloom throughout the region, with estimated full bloom in McIntosh on May 6 in Deerfield, Michigan. Although the week was wet, we seem to be past the threat of freezing temperatures. We continue to see blossoms in cherries and peaches, but pears and plums are mostly post-bloom. We expect scattered showers tonight and again over the weekend, but temperatures should warm to the low 70s.

The continued chance of rain means that disease risk will still be present. Warm and wet conditions are favorable for fire blight, and models indicate higher risk beginning Saturday, May 13, and continuing into next week. Based on the RimPro models at the Romeo station, for which you can see you an overview by following the link, we may see we are expecting continued potential for apple scab infection beginning Saturday and continuing into next week.

We have started to see more insect movement in the last week and I have begun to set up traps to monitor invasive species. I have received reports of some catches of oriental fruit moth (not sustained) and climbing numbers of redbanded leafrollers. Obliquebanded leafroller larvae are starting to be seen. With apple bloom happening, this is a good chance to review this 2022 article on reducing pesticide risks to bees during fruit crop bloom.

I encourage our growers to attend the weekly southern Michigan grower meetings virtually on Monday evenings by registering at MSU CANR Events. 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. Blooms are being seen across the region. Deerfield and Novi are mostly at full bloom, while further north in Fenton, Romeo and Almont, more trees are at King Bloom. RimPro is currently reporting a lingering risk of a scab infection through the next day of continued rain and potentially again around May 10. Critical temperatures for apples at first bloom are 28 degrees Fahrenheit for 10% kill and 25 F for 90% kill. At the full bloom stage, they are 29 F for 10% kill and 25 F for 90% kill.

You may want to read this 2022 Michigan State University Extension article on crop load management to prepare for whether and how you may want to treat your trees during bloom to ensure return bloom and marketable fruit size.

As mentioned above with the warm and wet conditions, we may see soon there is potential for fire blight. Washington State Extension has a comprehensive article on fire blight, including various control and prevention options.

Blueberries. We have late pink bud in blueberry plantings in Fenton and I found an open flower when I went looking. This is the primary risk period for mummy berry, especially with rain coming this weekend. It is also time to start paying attention to phomopsis. FRAC 3 fungicides are reported to be efficacious for both mummy berry and phomopsis. The critical temperatures for damage for blueberries at late pink bud is 24-27 F and full bloom 28 F.

Brambles. We are seeing fruit buds in red raspberries in Romeo and Fenton and black raspberries in Washtenaw County. We are still at prebloom so there is still time for delayed dormant sprays. See the Fruit Management Guide (E-154) for more information.

Cherries. Sweet cherries in Romeo are past petal fall while tart cherries in Novi, Fenton, Romeo and Almont are in full bloom. Expansion of first bract leaves is the beginning of risk period for cherry leaf spot. The critical temperatures for sweet cherries post bloom are 30 F for 10% kill and 28 F for 90% kill. The critical temperatures for tart cherries at full bloom are 28 F for 10% kill and 24 F for 90% kill.

Grapes. We have seen bud burst in Fenton and Marquette and Itasca vines in Ray Township. The critical temperatures for grapes (hybrid and vinifera) at bud burst are 28 F for 10% kill and 25 F for 50% kill. The critical temperatures grapes at full swell are 26 F for 10% kill and 21 F for 50% kill.

This slow grape bud development period is a good chance to monitor for cutworms and flea beetles. Please see this article for scouting guidance (note the Lorsban recommendation is out of date).

Strawberries. Vegetative growth continues in field strawberries in Romeo. In southwest Michigan, bloom is starting on protected plants. Flowers can be killed at 10 F temperatures while still in the ground at 20 F temperatures once emerged. Early season fungicides should focus on controlling leaf spot.

Peaches and nectarines. Peaches in Fenton remain at full bloom and blooming is winding down into petal fall in Romeo. At full bloom, critical temperatures are 27 F for 10% kill and 24 F for 90% kill.

Pears. European pears observed at Novi are at petal fall. At petal fall, the critical temperatures for pear are 28 F for 10% kill and 24 F for 90% kill.

Plums. European plums observed in Fenton are at petal fall. The critical periods for most fungal control is for 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 petal fall are 28 F for 10% kill and 23 F for 90% kill.

Insect conditions

Our main message from our integrated pest management (IPM) educators is to avoid applying insecticides during bloom! Many insecticides will also harm or kill bees and other pollinators that are necessary to ensure a good fruit crop. With apple bloom imminent, this is a good chance to review this 2022 article on reducing pesticide risks to bees during fruit crop bloom.

I have started to set up trap line traps for both Michigan Department of Agriculture and Rurarl Development (MDARD) and MSU fruit research. These include traps for plum curculio, light brown apple moth, summer fruit tortrix moth, plum fruit moth, oriental cherry fruit fly, wooly apple aphid and San Jose scale in addition to scouting for spotted lanternfly. I will keep you up to date on these as needed.

In tree fruit, our insect concerns include mites, scale, rosy apple aphid, 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). The E-154 guide can be purchased here: https://shop.msu.edu/products/bulletin-e0154.

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.

Green fruitworm: If necessary, you can use a broad spectrum insecticide like Grandevo before or after bloom in apples and stone fruit. Some adults have been observed in the region.

Mites: Treatment begins after petal fall.

Oriental fruit moth: We haven’t had sustained catches, but flight has been observed in Bruce Township. It is time to think about mating disruption before emergence.

Pear psylla: We are past the time for early control with dormant oil. Later on, control reducing vegetative flushes and hand removing suckers.

Plum curculio: This pest is active during bloom but not on fruit, which is where damage is. Plum curculio management is usually done at petal fall because most sprays for plum curculio are also toxic to bees. Options for management include contact pesticides to kill feeding adults, pyrethroids or Avaunt (non-contact poison, ingestible). At five to seven days post-petal fall, there is enough of a fruitlet for oviposition, so neonicotinoids can be applied as an oviposition deterrent. In stone fruit, neonicotinoids can be applied at shuck split. Nothing should be applied before (no fruit) and during bloom to protect pollinators.

Redbanded leafroller: Numbers are climbing in the region. While we are currently below threshold, we expect to pass it this week.

Rosy apple aphid: Some have been observed in Fenton and South Lyon.

San Jose scale: We are past the time for early season dormant oil applications. The next opportunity to control them is during their crawler stage around the second cover in apples.

Spotted tentiform leafminer: Low numbers have been observed in the region.

Tarnished plant bug: These are usually present on orchard floors, though they tend not to be a major issue. The tarnished plant bug can damage flowers and developing fruit. Do not apply anything during bloom.

Seasonal weather update

The milder weather the last week has pushed apples into bloom throughout the region. Although the week was wet, we seem to be past the threat of freezing temperatures. We expect scattered showers tonight, May 9, and again over the weekend. Temperatures should warm to the low 70s through Friday, May 12. Early next week we expect cool and dry conditions.

We have had about a half-inch of liquid precipitation in the last week (see table below). Our low temperatures have been well above the critical temperatures for our fruit crops. As always, it will be wise to stay alert to changing weather conditions in the next week.

The medium range guidance calls for a return of cooler than normal temperatures next week and the following week with below normal precipitation totals.

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 (GDD) accumulation for the season has regressed closer to the five-year average compared to last week, exceeding the average by 31 GDD at 42 F, 19 GDD at 45 F and 21 GDD at 50 F (see table below, these numbers would be even smaller but I added in a few more stations to the table this week). Read this Michigan State University Extension article to learn more about degree days: Understanding growing degree-days.

Watch Jeff Andresen's weekly 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.