Grand Rapids area tree fruit update – May 14, 2024
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Weather update
The Grand Rapids, Michigan, area is anticipating rain Thursday night, May 16, into Friday. We are heading into warmer weather this week with highs in the 70s and into the 80s on Sunday. This will be a nice window of weather for thinning.
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 past bloom and focused on thinning this 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.
Also, consider the NEWA carbohydrate model when choosing your thinning windows. This model will evaluate tree stress, which impacts thinning efficacy. The more stressed trees are, the more likely they are to drop fruitlets when sprayed with thinners. May 12 – 15 has been rated to have very good thinning efficacy and low risk for overthinning.
This week, we will continue to have weather in the 70s with cloudy conditions. The heat later this week will allow for more effective thinning.
|
Growing degree day (GDD) accumulation since Jan. 1 as of May 14, 2024 |
5-year average |
|||
|
Stations |
GDD42F |
GDD50F |
GDD42F |
GDD50F |
|
Aetna-Fremont |
573 |
248 |
389 |
181.3 |
|
Alpine |
663 |
315 |
437.1 |
204.8 |
|
Belding |
637 |
299 |
402.2 |
183.8 |
|
Conklin |
644 |
300 |
425.5 |
197.5 |
|
Grant |
627 |
291 |
391.4 |
177.5 |
|
Kent City |
622 |
284 |
383.5 |
173.4 |
|
Sparta |
640 |
299 |
394.1 |
177.9 |
|
Sparta-Tower |
642 |
299 |
401 |
181.1 |
|
Sparta-North |
636 |
293 |
421.4 |
196.1 |
|
Standale |
709 |
351 |
443.5 |
205.5 |
|
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 2% of remaining ascospores are still immature and another 7% are mature and ready to eject this week. With the warm and mostly dry weather this week, we are anticipating minimal spore ejections until the predicted rain next Monday – Wednesday (May 20 – 22). This period is currently predicted to be a high infection risk event. The rain this Thursday night (May 16) into Friday is predicted to be a small infection risk event.
After the rain next week, we’ll have very few spores remaining. However, all spores count! No matter how few spores we catch, they all matter for controlling secondary scab.
The rain event from 1 p.m. May 7 through 9 a.m. May 8 had a moderate risk with 476 spores released. Any associated symptoms from this infection event will show up around May 19.
|
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 |
|
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. |
None |
Fire blight
Blossom blight
Spray for blossom blight if you have any remaining blooms open. The epiphytic infection potentials (EIP) are over 70 from May 15 – 19. Of note, May 18 and 19 are both over 100, which is the critical point for infection in the model. This really only applies for rattail blooms in the Grand Rapids area but can still be concerning for some.
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.
I caught one codling moth this week. If I catch them again next week, we will set the biofix.
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.
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.
