Grand Rapids area tree fruit update – June 4, 2024

Lindsay Brown<brow1111@msu.edu>, Michigan State University Extension  - June 04, 2024

The Grand Rapids area is moving into second cover timing.

Gala apple fruitlets. — Fruitlets are starting to color. Photo by Lindsay Brown, MSU Extension.

The Grand Rapids, Michigan, region is anticipating rain on Wednesday, June 5, and a cold front following for the remainder of the week.

For a detailed look at the upcoming weather forecast, Jeff Andresen, Michigan State University agricultural meteorologist, has weekly 15 - minute talks posted every Tuesday.

Crop update

We are entering June drop this week and fruit is starting to color.

Frost damage is becoming quite apparent on fruitlets. Frost rings and misshapen fruitlets are fairly widespread this season across varieties. Once June drop has settled, we will be able to better evaluate the impact this will have on the crop.

Fruitlets are squarely out of the chemical thinning window. Hand thinning will be required for any remaining crop load management this season.

Growing degree day (GDD) accumulation since Jan. 1 as of June 4, 2024			5-year average
Stations	GDD42F	GDD50F	GDD42F	GDD50F
Aetna-Fremont	1016	527	815	453
Alpine	1121	609	879	492
Belding	1089	590	824	452
Conklin	1111	601	874	488
Grant	1078	580	804	438
Kent City	1083	580	802	436
Sparta	1101	594	812	441
Sparta-Tower	1098	589	822	446
Sparta-North	1092	583	861	480
Standale	1177	655	878	486

McIntosh growth stages	GDD42F	GDD50F
First cover	749	401
Second cover	1061	607
Third cover	1405	842

We typically report GDD accumulation starting at March 1, but this is not a typical year. We reached the required chilling hours on Jan. 15 to move into ecodormancy and start accumulating GDD. This means the heat we received in February mattered for this year’s crop. As such, I will be reporting GDD from Jan. 1 rather than March 1 this season.  

Pest and disease update

Apple scab

We are moving towards the end of the primary apple scab season now. Only 0.002% of mature ascospores are remaining to eject from the leaf litter. I am anticipating it will take another few rain events to fully deplete the overwintering scab population. Please remain covered with fungicides until primary scab season is concluded and no secondary lesions can be detected with careful scouting.

However, all spores count! No matter how few spores we catch, they all matter for controlling secondary scab.

The rain event from 4 p.m. on June 1 through 10 a.m. on June 2 had a moderate risk level with an average of 13 ascospores per rod released. This rain event was associated with 196% progress towards infection. Any associated symptoms from this infection event will show up around June 10.

Timing	Spores/rod	Risk level
4/26 9PM - 4/27/2024 8AM	486	None
4/28 8 a.m. – 4/29/2024 1 p.m.	1384	Heavy
4/30 1 p.m. – 4/30/2024 2 p.m.	12570	None
5/1 6 a.m. – 5/1/2024 9 a.m.	6	None
5/2 8 p.m. – 5/3/2024 2 p.m.	2548	Moderate
5/4 11 p.m. – 5/5/2024 8 a.m.	1	None
5/7 1 p.m. – 5/8 9 a.m.	476	Moderate
5/11 1 a.m. – 5/11 11 a.m.	278	None
5/12 10 p.m. – 5/13 6 a.m.	278	None
5/20 11 a.m. – 5/21 12 p.m.	1020	Heavy
5/25 5 a.m. - 5/25 8 a.m.	24	None
5/26 5 p.m. - 5/28 10 a.m.	21	Heavy
6/1 4 p.m. - 6/2 10 a.m.	13	Moderate

Fire blight

Shoot blight

Shoot tips are still pliable and flexible this week. We strongly recommend using the combination of 2 ounces Actigard plus 1 ounce Apogee applications starting at king bloom petal fall and continuing every 10 days until shoots harden off. While the shoots are actively growing, they are more susceptible to shoot blight.

If you have any fire blight infections, please reach out to me at brow1111@msu.edu. The Sundin lab is looking to sample different bacterial isolates throughout the state this year.

Powdery mildew

While primary powdery mildew lesions will stop sporulating this week, secondary lesions are continuing to develop. I am seeing powdery mildew take over whole shoots this week. Keeping control over powdery mildew now will prevent it from becoming a wider spread issue later in the season.

Fruit rot

Start incorporating control measures for bitter rot and black rot now. Mummies and fallen fruit contain inoculum for this season. They are beginning to sporulate and infect at this point in the season.

Sooty blotch and fly speck

While these two fungal diseases appear later in the growing season, their control window starts now. Summer diseases need springtime control.

Insects

Codling moth adult populations look to be decreasing in the area, but first-generation egglaying and egg hatch is expected this week. If an ovicide like Rimon was used at 100 GDD after the biofix, then consider a second ovicidal application now. Additionally, if a larvicidal compound was not used at 250 GDD after the biofix, then consider a larvicide this week.

Obliquebanded leafroller larvae are active in the area. I have not caught adults yet.

No green fruitworms were caught in my traps this week.

I did not catch oriental fruit moth this week. They currently have low populations in the area as we are in between generations. I expect the next generation to begin emerging in the next week.

A few spotted tentiform leafminers were found in my traps this week. Given that I did not catch them last week, I would expect this is the beginning of their second generation.

Potato leafhoppers are currently in the area. Keep an eye out for them in sticky traps and on the undersides of leaves. Look out for stippled chlorosis, burnt leaf margins or cupping of young terminal leaves.

Woolly apple aphid colonies are still active in some orchards. If you used a spirotetramat treatment during the petal fall through first cover timing window, be sure to wait 10 to 14 days after application to make sure the product has taken effect before planning another spray.

San Jose scale crawlers are active in south Michigan this week. I am seeing San Jose scale parasitoids in my traps, but not flyers or crawlers yet. I would expect crawlers to be present in the area shortly based on growing degree days.

Tufted apple budmoth and rose chafer are also listed as insects of interest for second cover.

For more information about regional reports, please visit the Michigan State University Extension website.

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