Northwest Michigan fruit update – May 27, 2025
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EmailWith the cooler temperatures, many apples are still in bloom in the north. Growers are balancing disease control management with the cool weather.
Weather report
This cool weather has slowed the season during this past week. We are at petal fall in Honeycrisp at the Northwest Michigan Horticulture Research Center. We are in bloom further north, and Gala are at 75% bloom near East Leland. Although the growing degree days (GDDs) are normal, it has felt cold and plant movement has been slowed. For example, the lilacs at my house just north of Suttons Bay are not even in full bloom. In most years, we have lilac bloom around Mother’s Day.
According to Jeff Andresen, Michigan State University (MSU) climatologist, there will be increasing clouds on Tuesday, May 27, and rain is in the forecast for Wednesday in central and southern Michigan. There is some rainfall in the forecast for Friday, but the weekend weather is predicted to be warmer and drier.
The medium range outlooks call for a return of warmer than normal weather next week. Precipitation totals are forecast to remain at normal to below normal levels early, increasing to normal to above normal levels by the second week of June.
Crop report
The crop development continues to move along, and it has been slowed with the cool weather. We have varying crop development with the cool weather, followed by six days of warm weather, followed by cool weather. There have been many reports of varying degrees of bloom across the board in all tree fruit crops this year. Montmorency tart cherry is at or near shuck split at the Northwest Michigan Horticulture Research Center, however, we did observe new open blooms last Friday in Montmorency in Kewadin.
Sweet cherries are sizing, and all varieties are 6-8 millimeters (mm) at the Northwest Michigan Horticulture Research Center. These fruit are susceptible to plum curculio oviposition once the fruit comes out of the shuck. Gala and Honeycrisp are at open cluster to petal fall. However, again, there is variability across the trees and branches with development. Again, it seems cold here in the north, and it is surprising to see open blooms at the end of May.
Disease report
In general, growers are going to be challenged in making disease control decisions this week because the weather forecasts continue to change. The weather is cool, but we have had significant wetting events. The question is to spray for disease or not with the cold and wet weather.
Apple scab
Again, growers need to be protecting the new growth in apples from apple scab. This disease is favored by warm and wet conditions. We have had wet weather, but the temperatures remained cool. In this situation, growers have been wondering if and when to pull the trigger for scab control. This disease, unlike cherry leaf spot, can be controlled early and growers will not have to manage it all season. Therefore, growers need to protect now to prevent further maintenance down the road. We recommend using EBDC materials with another mode of action at this time.
The MSU fruit team will be using the RIMpro model to help growers manage apple scab throughout the season. Michigan State University Extension is a great article on how to use RIMPro to best predict scab in regional orchards. There are significantly more spores mature this week than at this same time last week.
Here are the following links for RIMpro outputs from May 27.
Powdery mildew
The weather has not been conducive for powdery mildew, but orchards that have had powdery mildew problems in the past should be on the offensive to control this disease. This fungus is able to cause spring and early-summer epidemics, starting from the green tip stage until the end of new shoot growth. In apples, the fungus overwinters in the form of mycelia in dormant buds. Because infected buds open later than healthy ones there is a higher risk of infection when conidia released from the infected buds infect new leaves that have emerged earlier from healthy buds.
Additionally, the fungus may also survive as cleistothecia (sexual bodies) on stems or leaves. According to Washington State University, “temperature is the primary environmental factor that has the most significant impact on the development of mildew.” The optimal temperature range for spore release is between 59 and 68 degrees Fahrenheit, while germination is optimal at 68 F for P. leucotricha. The incubation period, prior to the emergence of the first symptoms, can vary from three to 12 days depending on the temperature, with an average of eight days under favorable conditions. Temperatures below 50 F and above 86 F significantly inhibit growth and infections. For powdery mildew control, single site fungicides should be used at this timing: SHDIs (Miravis, Tesaris, Merivon), QoIs (Flint Extra) and DMIs (Rhyme).
American brown rot
In most areas in northern Michigan, we are out of the window for American brown rot control for blossom blight.
Cherry leaf spot
Growers need to be controlling for cherry leaf spot now. We have had long wetting periods, but it has been cold. This situation is difficult, because it is so cool, but the wetting periods have been long. Because cherry leaf spot is ubiquitous in the orchard, growers should be conservative in their control options. The following table is the infection table from Andrew Jones of Michigan State University. We should have an infection if the wetting period is long enough, even when it is cool. We would need 25 hours of wetting to trigger an event if the temperature is 47 F.
Table 1. Approximate minimum number of hours of leaf wetness required to produce leaf spot infections caused by conidia on sour cherries.¹
|
Average temperature (degrees F) |
Wetness (hours)² |
Average temperature (degrees F) |
Wetness (hours) |
|
46 |
28 |
61-62 |
6 |
|
47 |
25 |
63-68 |
5 |
|
48 |
23 |
69-70 |
6 |
|
49 |
20 |
71-72 |
7 |
|
50 |
19 |
73 |
8 |
|
51 |
17 |
74 |
9 |
|
52 |
15 |
75 |
11 |
|
53 |
14 |
76 |
12 |
|
54 |
12 |
77 |
14 |
|
55 |
11 |
78 |
16 |
|
56 |
10 |
79 |
18 |
|
57 |
9 |
80 |
21 |
|
58 |
8 |
81 |
28 |
|
59-60 |
7 |
|
|
|
¹Requirements for primary (ascospore) infections are presumed to be similar. |
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Pest report
We have caught few insects with cold temperatures, but we did catch our first codling moths and one lesser peachtree borer this week. We also caught more black stem borers this week, but numbers are lower than last week.
Green fruitworm
We have caught no green fruitworm moths this week.
Black stem borer
We caught one black stem borer this week. As expected with the cool temperatures, this pest activity will increase or decrease with the temperatures. Growers with black stem borer issues in the past should do trunk sprays when the daytime temperatures warm this week.
San Jose scale
We did not catch San Jose scale in traps again this week, but they were caught at the Trevor Nichols Research Center. If growers missed oil at the delayed dormant timing, recent data show that Esteem 0.86EC at 16 ounces at pink provided excellent control of San Jose scale in a particularly high-pressure block. Centaur 70WDG at a rate of 34.5 ounces at the pink timing provided good control of this pest. In short, if growers missed their oil applications, they should target the pink stage with Esteem or Centaur. Growers should be trying to control this pest when the conditions warm.
Plum curculio
Growers should be controlling this pest at this time in cherry. At the Northwest Michigan Horticulture Research Center, we have observed sweet cherries at 6-8 mm, and plum curculio will oviposit into this fruit. Plum curculio becomes active with overnight temperatures over 65 F, and they do prefer moisture or humidity to increase activity. The females will oviposit eggs into the fruit as soon as the fruitlet is visible. With the recent overnight higher relative humidity and isolated rainfall, plum curculio activity will likely increase, and fruit is at a susceptible stage. “Effectively controlling plum curculio in stone and pome fruits” is a good article on managing plum curculio. Growers should be aware of Avuant and neonicotinoid options at this time because Avaunt needs to be ingested, and neonics are anti-feedants.
This work is supported by the Crop Protection and Pest Management Program [grant no 2024-70006-43569] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
