MSU Extension Fruit & Nuts

Welcome to the seventh 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

While most of our region was cool and dry last week, we did see some areas of frost on Thursday morning, May 18, that caused some damage in a few crops. We continue to see the tail end of blossoms in apples in more northern parts of the region, but cherries, peaches, pears and plums are mostly post-bloom. Blueberries and strawberries continue to bloom while I saw my first blossoms in raspberries for the season. We are starting to see inflorescences swelling in grapes. We expect cool and dry weather through the weekend with temperatures rising at the end of next week. There is potential for rain tonight and the potential for a dip into the 30s overnight Wednesday into Thursday, so you may need to prepare for frost protection.

We expect continued dry weather in the coming weeks, so if you have irrigation systems you should consider preparing them for use.

The continued dry weather should keep disease risk at bay. Based on the RimPro models at the Romeo station, for which you can see you an overview by following the link, we may see continued potential for apple powdery mildew. I have received reports of some mild 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 received reports of sustained catch of codling moth (May 18 biofix, but some growers reported catch before then), threshold numbers of redbanded leafrollers and larvae of obliquebanded leafrollers (below threshold). Plum curculio has been seen, but numbers remain low. With small fruit bloom in some areas, this is a good chance to review this 2022 article on reducing pesticide risks to bees during fruit crop bloom. In addition to insect movement, we are also seeing more activity from mammals like deer. Make sure to do your normal preparations for protection from animal damage.

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 in the 0.25- to 0.5-inch fruitlet diameter range, while further north in Fenton, Romeo and Almont, fruitlet size is a bit smaller while some trees are hanging on to blossoms.

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. If you are concerned about bitter pit (especially in Honeycrisp production) now would be the time to prepare for calcium sprays.

Blueberries: We have hit bloom in blueberry plantings in Fenton. We are approaching the end of the primary risk period for mummy berry. Sprays still 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. In southwest Michigan, cranberry fruitworm adults are starting to fly, and these can be a problem in blueberry crops. The critical temperatures for damage for blueberries at full bloom is 28 F.

Brambles: We are seeing flowers in red raspberries in Romeo. There are floral buds on blackberry in Lenawee County.

Cherries: Sweet cherries in Romeo and Fenton are at fruit set up to 0.5-inch while tart cherries in Novi, Fenton and Romeo are set around 0.25 inches. We saw some damage in tart cherries in Lapeer County in the last week. The critical temperatures for cherries post bloom are 30 F for 10% kill and 28 F for 90% kill.

Grapes: We have seen plentiful shoot growth in Fenton and Ray Township in addition to swelling inflorescences. We saw some cold damage last week in some cultivars in Ray Township.

Strawberries: We have seen blossoms in field strawberries in Romeo and Fenton. Flowers can be killed by 10 F temperatures while still in the ground at 20 F temperatures once emerged. Early season fungicides should focus on controlling leaf spot. Some growers in Macomb County reported some damage in strawberries after the cold last week.

Peaches and nectarines: Peaches in Fenton are mostly at fruit set with some remaining petals while peaches in Romeo were 0.25-inches in diameter. At post-bloom, critical temperatures are 28 F for 10% kill and 25 F for 90% kill.

Pears: European pears observed at Novi are roughly 0.25-inch in size. 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.

Disease conditions

With the upcoming dry weather, we don’t expect infection periods for apple/pear scab, fire blight, grape black rot or apple canker.

Apple powdery mildew has been seen in the region, but reports indicate it is mild.

Apple scab has been reported in the region in susceptible cultivars and locations.

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 had live catches of codling moth over the last week (though I received a report from a grower of it being caught earlier). I have biofix set at May 18. 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 a week).

Grape berry moth: This pest attacks developing grape clusters. Watch for wild grape bloom to indicate biofix. Second and third generation control are most effective at reducing infestations during harvest.

Mites: Treatment begins after petal fall.

Obliquebanded leafroller: A few larvae have been seen by scouts, but because these are usually controlled with the pink spray, there haven’t been any threshold catches.

Oriental fruit moth: We have had sustained catches in the region (biofix May 11). Products with ovicidal activity are suggested for about 100-150 GDD45 after biofix (should be your next cover if not already applied).

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 caught one in Washtenaw County last week. 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. This likely would have been taken care of in your petal fall spray.

Rosy apple aphid: Can be seen curled in leaves around the region.

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: First adult flight is over in most of 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.

Woolly apple aphid: Some have been observed by regional scouts, but management is usually done later in the summer.

Seasonal weather update

The past week has been dry with an average of less than a half inch of rain in the region. Temperatures have been below normal ranging from cool to cold, with some frost damage occurring overnight last Wednesday. We are seeing some effects from wildfires in Canada with hazy skies reducing our sunlight exposure. The dry weather since the beginning of the month has been pushing our soil moisture down. This is forecast to continue, so you may need to consider irrigation, especially in younger plantings.

In the next week we expect fair and dry conditions to continue. The exceptions are some overnight showers tonight (May 23) and potentially some scattered showers later this week in the Saginaw Bay area. This weather should continue into the start of next week.

We have had little 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 above normal temperatures.

The long lead outlooks are still calling for wetter than normal conditions for the late spring and summer seasons, but these forecasts have shifted towards expected normal temperatures.

Our regional average growing degree day accumulation for the season continue to remain a few days ahead of 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.