MSU Extension Fruit & Nuts

Weather report 

The weather is all over the board this week. We had a cool weekend, and daytime temperatures at the Northwest Michigan Horticulture Research Center on Saturday, May 31 topped out at 56.4 degrees Fahrenheit. Overnight temperatures dipped into the high 30s. We had slightly warmer, at least sunnier, weather on Sunday, June 1, where the daytime highs hit 62 F and the overnight temperatures were also in the high 30s. However, in some areas, there was reported frost, even in Leelanau County near the lake. Further inland, more freezing temperatures were reported. We have heard few reports of damage to fruit crops with the recent overnight lows.  

The beginning of this week is feeling a bit more summer-like as yesterday (June 2) and today were in the high 70s and may even hit over 80 F in Traverse City. However, there is a slow-moving front coming in from the west bringing rain and cooler weather through the remainder of the week and into the weekend. Daytime high predictions seem to vary by weather app, but the temperatures are predicted to cool with the rain.  

Growing degree day (GDD) accumulations are showing conditions have been cool, and even parts of southern Michigan have cooled compared to the start of the season when they had warmer than normal conditions for weeks. For 2025, at the Northwest Michigan Horticulture Research Center, we have accumulated 363.6 GDD base 42 and 313.8 GDD base 50. We are behind our 35-year average: 689.9 GDD base 42 and 357.1 GDD base 50. Despite the lag in GDD accumulations, the weather conditions have seemed particularly cool. Conditions have also been windy, which has made the temperatures feel cooler, especially if the wind is coming from the north or off Lake Michigan.  

The forecasts are also predicting rain. As mentioned above, there is a system coming from the west, but it is moving slowly; it is predicted to be here by early Wednesday, and the rainfall potential is high. Jeff Andresen, Michigan State University (MSU) climatologist, predicts the north will receive more rain than other parts of the state for tomorrow, and we may see up to an inch of rain in some places. Conditions are dry across the region, and we could use the rain. There is rain in the forecast for Sunday, June 8.  

According to Andresen, there has been less confidence in the weather forecasts due to uncertainty. Most growers will likely agree with Andresen as the weather predictions change almost daily, and the swings between warm and cold seem extreme. The medium range forecast is predicting the temperatures to be near normal through mid-June while precipitation is expected to be higher than normal.  

Crop report 

Crop development continues to move along despite the variable weather. Conditions in the orchard are dry, and rain would be welcome. Tart cherries appear slow to come out of the shuck here at the Northwest Michigan Horticulture Research Center, which is likely an indicator that many fruit are not coming out of the shuck. We have measured cherries at 10-11 millimeters (mm), but there are few cherries in our orchards. We likely have considerable damage. There are still occasional blooms popping open, but those random blossoms have slowed since last week. 

Sweet cherries are sizing, and all varieties are 11-13 mm at the Northwest Michigan Horticulture Research Center. Gala and Honeycrisp fruit are sizing, and king fruit are 7 mm. There is tag bloom in apples at the Northwest Michigan Horticulture Research Center, but there are still blooms in apples to the north. Growers need to be controlling for fire blight with open bloom, and rain in the forecast.  

We have observed some unusual development in tart and sweet cherries in orchards around the region (Photos 2 and 3). The trees appear to be extremely slow to grow, and leaves are not growing but at the tips of the branches. Many buds have not opened giving the branch a blank appearance. The leaves that are growing are distorted, darker in color and almost crinkly in appearance. There is also a lot of blossom blast in tart cherries. The flowers and shucks look red/brown on the tree are not falling. There are no fruit emerging from these flowers but still are not falling.  

The trees that are most affected in the orchard are on sandy knobs, and the symptoms are more evident in orchards with poor soil, either sandy or gravelly. We are trying to understand the cause of this situation, but we hypothesize that the cold weather of April 29-30 contributed to the problem. These trees may be weaker on poorer quality soils and more susceptible to winter damage. We are testing foliar sprays of boron and zinc to help jump start tree growth after sustained cold damage followed by cold temperatures this spring. 

Disease report 

Fire blight

There are varying amounts of bloom in apple orchards across the region. Many growers in the south, Benzie, Manistee, and up through southern Leelanau and Grand Traverse, have starting their thinning. However, there are tag blooms on the trees, and growers to the north still have significant amounts of bloom on the trees. With the warm weather and rain in the forecast, growers with bloom on trees need to be controlling for fire blight.  

The fire blight model for the Northwest Michigan Horticulture Research Center shows that today, tomorrow and Wednesday (June 3-5) have high risk for infection. EIPs for these dates are as follows: 186, 816 and 211 (Photo 3). These are very high EIPs, particularly with rain in the forecast. Growers need to be using Kasumin in orchards with strep-resistance fire blight bacteria. If growers know that streptomycin is still efficacious in their orchards, this material can be used.  

Kasumin is an excellent fire blight material. It provides forward control for two to four days prior to rain events and will be effective for blossom blight control if applied within 12 hours after a rain event. Kasumin is used at a rate of 2 quarts (64 fluid ounces) per acre in 100 gallons of water per acre and should be applied with a non-ionic surfactant (1 pint per 100 gallons). Read the label carefully as there are some specifications, including: 

• Do not apply Kasumin in orchards in which the soil has been fertilized with animal manure. 
• Do not apply after petal fall. 
• Do not use alternate row applications. 

The main difference between Kasumin and streptomycin is that Kasumin is not partially systemic like streptomycin is. Thus, Kasumin will not penetrate into the nectaries and will not be able to control an infection once the fire blight pathogen reaches the nectaries. 

Apple scab

Growers need to be actively controlling scab with the coming rains. According to the MSU Enviroweather scab model, we are at 98% mature spores and 83% dispersed spores. This means we are not at the end of primary scab. Use good materials to control scab, as this rain event may trigger the end of primary for the season. Use materials such as Inspire Super, Cevya, SDHI fungicides or the new fungicide Axios. All materials have shown excellent efficacy in MSU scab trials. Michigan State University Extension recommends these single site fungicides be tank-mixed with protectants, such as Captan or EBDCs. EBDCs have a long preharvest intervals (PHI): 77days prior to harvest. Growers with early apple varieties should keep an eye on this PHI. 

The MSU fruit team will be using the RIMpro model to help growers manage apple scab throughout the season. Michigan State University Extension has 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 June 3:  

• Williamsburg  
• Benzonia  
• East Leland  

Powdery mildew

For powdery mildew control, single site fungicides should be used at this timing: SHDIs (Miravis, Tesaris, Merivon), QoIs (Flint Extra) and DMIs (Rhyme). Many of the materials used for scab control will also control powdery mildew.  

Cherry leaf spot

Growers need to be controlling for cherry leaf spot with the predicted rain event. Unlike scab, leaf spot is a disease that continues to be active throughout the season, so control it early in the season to minimize secondary infection in the canopy. Thus far this season, we have isolated infection periods for this disease because it has been cool, and this disease is a slow growing fungus. However, we have had a high and a moderate leaf spot infection at the Northwest Michigan Horticulture Research Center on May 15 and 18.  

Captan is an excellent material for leaf spot. It continues to perform well in all cherry leaf spot efficacy trials even when used alone throughout the season. Copper materials are also rated excellent for leaf spot control. We have new data on the efficacy for leaf spot management comparing the different copper materials. Cool weather is a great time for copper use against leaf spot to minimize the potential for phytotoxity to leaves. Flint Extra, a strobulurin, is also excellent against leaf spot.  

Pest report 

We have caught few insects with cold temperatures, but activity will increase with the warm weather for the next two days.  

American plum borer

We caught an average of 8.3 moths this week, which is just one more than last week.  

Lesser peachtree borer

We caught one moth last week, and an average of 2.3 moths this week. 

Black stem borer

None were caught this week. As expected with the cool temperatures, this pest activity will increase or decrease with the temperatures. 

San Jose scale

Non were caught this week. They did not catch males at the Trevor Nichols Research Center either, but they did see crawlers in apple and sweet cherry.  

Plum curculio

Now is the time to control this pest in cherry. Sweet cherries are 11-13 mm at the Northwest Michigan Horticulture Research Center, and plum curculio will oviposit into this fruit. Growers have reported plum curculio stings in cherry fruit, and one grower saw an actual female trying to oviposit in apple late last week. These insects are out and active, particularly with this warm weather. This pest can sneak up on cherry growers whose main focus is spotted wing Drosophila, so be aware that plum curculio is active in orchards now. “Effectively controlling plum curculio in stone and pome fruits” is a good article on managing plum curculio. Be aware of Avuant and neonicotinoid options because Avaunt needs to be ingested, and neonics are anti-feedants.  

Thinning 

Growers should be cautious about thinning this year as some orchards may have sustained damage from April cold weather. There is also a wider range of phenological stages on trees this season, which is likely due to changes in temperature with mixed conditions of warm then cool temperatures. This may be helpful for thinning as king fruit will be more competitive than the lateral fruit, and laterals will be more affected by chemical thinners. 

As Emily Lavely, MSU Extension tree fruit educator, reported last week, “There have been some reports about the variability in set across varieties. We are recommending growers scout orchards block by block to determine if a chemical thinner is needed. It is important to scout orchards on foot this season. There is more foliage now than is typically seen at thinning time, and it is difficult to see fruitlets that are there without close inspection. Also, look throughout the canopy as fruit set is often higher in the top of the tree compared to the bottom.  

“As a reminder, measure fruit daily or every few days to determine if fruit are continuing to grow or if they stop growing. Use the fruit growth rate model to determine fruit set and efficacy of thinner applications. As a reminder, fruit that continue to grow steadily will persist, and fruitlets that are growing at a rate of 50% or less than the fastest growing fruit will abscise.” 

According to the MSU Apple Thinning Guide, thinning sensitivity is low at petal fall, greatest at 10 mm, and then quickly becomes insensitive at 2 5mm. At the Northwest Michigan Horticulture Research Center, apple fruit is at 7 mm for Honeycrisp and Gala, but there are smaller fruitlets on the tree. Growers have begun thinning in southern parts of northwest Michigan, as these warm weather conditions may be the only chance for thinning this season. Warm and cloudy conditions will promote thinning, and under cool and sunny weather, thinners will be less effective. Hopefully, the temperatures will not drop too much after this rain event so growers that are further behind can make some thinning decisions.