MSU Extension Fruit & Nuts

Welcome to the sixth 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 mild weather the last week has pushed many of our tree fruit crops through bloom with small fruits on their heels. We continue to see blossoms in apples in more northern parts of the region, but cherries, peaches, pears and plums are mostly post-bloom. Blueberries and strawberries have started to bloom while brambles and grapes are moving along with their vegetative growth. We expect cool and dry weather through the weekend with temperatures rising at the end of next week. There is potential for rain Friday, May 19, into Saturday and with that the risk for some disease infection.

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 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 with the rain events. We are also in the midst of a powdery mildew infection period. I have received reports of some powdery mildew on apples in parts of orchards with insufficient spray coverage. If you are having trouble with spraying, I highly recommend looking into the free resource Airblast 101.

We have started to see more insect movement in the last week and I have begun to monitor traps for invasive species. I have received reports of sustained catch of oriental fruit moth (May 11), threshold numbers of redbanded leafrollers. Codling moth has not yet been caught in the state, though our degree day models suggest it could happen any time. With apple bloom continuing in some areas, this is a good chance to review this 2022 Michigan State University Extension 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 Monday Night Southwest Michigan Fruit IPM Meeting 2023. 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: In southern parts of the region (Deerfield up to Novi), we are mostly at petal fall while further north in Fenton, Romeo and Almont, more trees are just approaching petal fall. Further north near Saginaw we are still at full bloom.

You may want to read this 2022 MSU Extension article on crop load management to prepare for whether and how you may want to treat your trees during and after 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 hit bloom in blueberry plantings in Fenton. This is the primary risk period for mummy berry, especially with rain coming this weekend. Sprays may be needed to protect the blossoms. 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 degrees Fahrenheit and full bloom 28 F.

Brambles: We are seeing fruit buds in red raspberries in Romeo and Fenton and black raspberries in Washtenaw County. There is considerable blackberry growth in Lenawee County.

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

Grapes: We have seen first leaves and shoot growth in Fenton and in 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 first leaf are 28.5 F for 10% kill and 27 F for 50% kill.

Strawberries: We have seen blossoms in field strawberries in Romeo. Flowers can be killed be 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 are at petal fall with some remaining blossoms and while we are at or past petal fall in Romeo. At post-bloom, critical temperatures are 28 F for 10% kill and 25 F for 90% kill.

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

Plums: European plums are well past bloom. The critical period for most fungal control is petal fall to late June, but for brown rot specifically the critical times are during bloom and later on at fruit coloring.

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 some growers still in apple bloom and small fruit bloom coming there is still time 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 Rural 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, woolly 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 current insect concerns include plum curculio, scale, tarnished plant bug, green fruitworm, oriental fruit moth, obliquebanded leafroller and codling moth. 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 at the MSU Bookstore.

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.

Codling moth: We have not had a live catch of codling moth yet in the state, though we expect it in the next week. This is your last chance for mating disruption. Once biofix happens, the next chance for control is to use selective products with ovicidal activity 100 growing degree days (GDD) base 50 after biofix (forecasted in about two 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 have had sustained catches in the region (biofix May 11). The next chance for control will be using products with ovicidal activity about 100-150 GDD base 45 after biofix (forecasted in about a week)

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

Plum curculio: Some adult plum curculios have been caught by a scout in the region. I have not caught any in my traps yet. 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, the neonicotinoids can be applied at shuck split. Nothing should be applied before bloom (no fruit), and nothing should be applied during bloom to protect pollinators.

Redbanded leafroller: We have reached threshold numbers for redbanded leafroller according to local scouts.

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. Some damage was seen by a scout in an area that had been mowed. The tarnished plant bug can damage flowers and developing fruit. Do not apply anything during bloom.

Seasonal weather update

The past week has been dry and relatively cool. This weather should continue into the start of next week. We have the potential for showers Friday, May 19, into Saturday. Next week, we expect to see warmer than average temperatures and dry conditions through the end of the month.

We have had little to no precipitation in the last week (see table below). Since we are past bloom in most fruit crops, the dry and cool temperatures should be favorable for cover sprays.

The medium range guidance calls for drier than normal weather with a gradual temperature warming in the next two weeks that will put us above normal.

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 continues to remain above average. 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.