Grand Rapids area tree fruit update – May 7, 2024

Lindsay Brown<brow1111@msu.edu>, Michigan State University Extension  - May 07, 2024

Petals are falling and sprayers are running this week on the Ridge.

For decorative purposes. — Gala at petal fall. Photo by Lindsay Brown, MSU Extension.

Weather update

Thunderstorms and showers are expected across the area Tuesday afternoon and evening, May 7. Hail may develop in very southern Michigan, but we are not anticipating hail in the Grand Rapids, Michigan, area. Scattered showers are expected again on Wednesday night into Thursday and potentially Saturday and Sunday.

The medium range outlooks call for near to/above normal mean temperatures and precipitation totals in the next few weeks.

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

The Grand Rapids area is now moving into petal fall. Be sure to focus on your thinning plans in the next week. The sooner thinning happens, the better for fruit quality. Consider this apple thinning strategies document from Michigan State University Extension when making your plans.

Growing degree-day (GDD) accumulation since Jan. 1 as of May 6, 2024			5-year average
Stations	GDD42F	GDD50F	GDD42F	GDD50F
Aetna-Fremont	465	198	317.4	132.6
Alpine	535	247	365.5	158.3
Belding	517	237	339.2	146.5
Conklin	519	236	351	149.5
Grant	508	229	327.4	138.7
Kent City	501	222	318.5	133.2
Sparta	514	233	329.6	139.1
Sparta-Tower	518	234	335.2	141.5
Sparta-North	515	393	349.1	148.2
Standale	575	276	375.6	165.1

McIntosh growth stages	GDD42F	GDD50F
Full bloom	422	205
Petal Fall	511	254
First cover	749	401

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. Approximately 10% of remaining ascospores are still immature and another 10% are mature and ready to eject this week.

We are looking at larger rain events on Tuesday and Thursday with showers possible almost every day this week. Tuesday’s rain is a high infection risk period and the remaining rain events this week will be slight to medium risk.

Timing	Spores/rod	Risk level
4/26 9 p.m. – 4/27 8 a.m.	486	None
4/28 8 a.m. – 4/29 1 p.m.	1,384	Heavy
4/30 1 p.m. – 4/30 2 p.m.	12,570	None
5/1 6 a.m. – 5/1 9 a.m.	6	None
5/2 8 p.m. – 5/3 2 p.m.	2548	Moderate
5/4 11 p.m. – 5/5 8 a.m.	1	None

Fire blight

Blossom blight

The warm temperatures and wetting events this week favor fire blight growth and infection. However, epiphytic infection potentials (EIP) will be below 70. The highest predicted EIP in the next week is for tomorrow, May 8, at 60. As such, oxytetracycline is recommended over kasumin or streptomycin.

The model on Enviroweather is highlighting many days as high risk in the past week due to the trio of bloom, wetting events and average daily temperatures over 60 degrees Fahrenheit. However, the EIPs have only been higher than 70 on two days: May 4 (86) and May 5 (74).

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.

Shoot blight

As we enter petal fall, consider your shoot blight management techniques. 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 especially susceptible to shoot blight.

Powdery mildew

Keep an eye out for any delayed blossoms that look distorted or weak. This is a sign of powdery mildew in the blooms.

Insects

Oriental fruit moth, green fruitworm, spotted tentiform leafminer, woolly apple aphid and flying San Jose scale have been detected in the region this week.

For woolly apple aphid, now is the time to make applications of spirotetramat products like Movento and Senstar. Keep in mind that Senstar also contains Movento. We are thinking about Movento now as it is systemic and can impact both the aerial colonies and the root colonies. Reducing the root colonies will reduce the aerial colonies over time as well! Spirotetramat is not immediately effective on adults, rather it limits their ability to reproduce. As such, you will not see immediate results. It will take one to two weeks to impact populations.

Keep pollinators in mind while making petal fall applications to ensure pollinator safety!

As we enter petal fall, keep in mind that this is a critical time for insect control for pests, including:

Woolly apple aphid
San Jose scale
White apple leafhopper
Tarnished plant bug
Plum curculio
Spotted tentiform leafminer
Obliquebanded leafroller
European red mite
Codling moth
Oriental fruit moth

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

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).