MSU Extension Fruit & Nuts

Weather report 

The weekend weather felt like summer, and daytime highs were in the mid-70s. This warmer weather was accompanied by sunshine for much of the weekend. Rain moved into the region on Sunday, June 8; the Northwest Michigan Horticulture Research Center Enviroweather station recorded 0.13 inches of rain. The rain moved out on Monday, June 9 during the day, and then more rain came into the region during the afternoon of June 9, and some of this rain was accompanied with thunder. The Northwest Michigan Horticulture Research Center Enviroweather station recorded 0.2 inches of rain for a total of 0.4 inches of rain for the past two days.  

We have heard reports of isolated but extensive hail damage on the east side of the region. Some growers have reported over 5 minutes of continual hail (Photo 1); growers are assessing hail damage in the affected areas.  

Growing degree day (GDD) accumulations are still showing that conditions have been cool. For 2025, at the Northwest Michigan Horticulture Research Center we have accumulated 781.1 GDD base 42 and 402.4 GDD base 50. We are behind our 35-year average: 836.1 GDD base 42 and 449.7 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 temperatures for the remainder of the week will continue to be cool, and overnight temperatures are predicted to be in the 40s and 50s. Daytime highs will be 60s for most days, and there is rain in the forecast for many days of the next week, but the percentages vary daily. There is a 50% chance of rain tomorrow, June 11 and another 50% chance on Friday, June 13. 

Crop report 

Crop development continues to move even with the cool weather. The rain has been a welcomed addition to the season as orchards were dry prior to these two last rain events. Tree growth has been excellent with the cool weather and now the rain, and orchards have a “lush” appearance. 

The tart cherry crop at the Northwest Michigan Horticulture Research Center is very light, and the fruit is at 12 millimeters (mm). There are many estimates about the size of the tart cherry crop this year, and it varies by area. The northern parts of northwest Michigan seem to have a bigger crop than the southern areas. The Michigan Cherry Committee estimates the crop in northwest Michigan is 50 million pounds. West central Michigan is also estimating their crop to be 50 million pounds. The growers in southwest Michigan estimate their crop to be 15 million pounds for a total of 115 million pounds of tart cherries in Michigan for 2025. 

Sweet cherries are sizing, and all varieties are 12-14 mm at the Northwest Michigan Horticulture Research Center.  

Gala and Honeycrisp apple fruit are sizing, and king fruit are about 14.5-15 mm. Although it is late in the season, we are still seeing occasional apple blooms in the orchard (Photo 2). Growers had a good window for thinning over the weekend with the warm temperatures. As temperatures cool this week, the carbohydrate model’s six-day weighted average is showing an excess in carbohydrates (above +15), and this excess will make thinning more difficult. With the cool weather plus an excess in carbohydrates, the model is recommending growers increase their thinning rates by 30%. Some orchards in the southern part of the region may be reaching the point where the fruit are too large to be thinned. Fruit above 20 mm in size is difficult to thin. We are still in the thinning window at the Northwest Michigan Horticulture Research Center.

Disease report 

Fire blight. Most orchards are out of the blossom blight period for fire blight. However, with the isolated hail and rain that came down yesterday, June 9, growers need to watch out for shoot blight. Some orchards likely had a trauma event with the extreme weather and shoot blight could be an issue. Growers need to be using Apogee and Actigard, which are critical materials to be applying in orchards to minimize potential shoot blight, especially in orchards with the excess growth that we are seeing this season.  

Research by George Sundin, PhD, at Michigan State University (MSU) conducted over the past few years measured the effectiveness of low-rate combinations of Apogee and Actigard on suppression of fire blight on apple trees. Two treatments of the Apogee and Actigard combination provided excellent suppression of fire blight. Treatments of 2 ounces of Apogee and 1 ounce of Actigard per acre applied starting at king bloom petal fall and then again 10 days later suppressed fire blight lesion development. In severe fire blight years, a third or forth application every 10 days may be necessary. The Apogee and Actigard combinations should be applied every 10 days. This strategy is critical to successfully control shoot blight, especially in high density orchards. 

Apple scab. We are close to calling the end of primary scab season. According to the Enviroweather scab model, we are at 100% mature spores and 92% dispersed spores. This means we are not at the end of primary scab, but close! We have also had daytime rains on Monday, June 9, and rainfall at this time likely ejects a fair number of spores. We had a moderate scab infection on June 8, and a light infection on June 9.  

Protect new growth from the scab fungus. We expect the end of primary scab to be soon with the rain in the forecast for multiple days for the following week. You should be using materials such as Inspire Super, Cevya, SDHI fungicides or the new fungicide Axios. All materials have shown excellent efficacy in MSU scab trials. We recommend that these single site fungicides be tank mixed with protectants, such as Captan or EBDCs. EBDCs have long preharvest intervals (PHIs): 77 days 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 control, single site fungicides should be used at this timing: SHDIs (Miravis, Tesaris, Merivon), QoIs (Flint Extra) and DMIs (Rhyme). Many of the materials that growers will be using for scab control will also control PM.  

Cherry leaf spot. We observed the first lesions from cherry leaf spot on untreated trees at the Northwest Michigan Horticulture Research Center. Most growers that have been actively controlling leaf spot in the orchard should not expect to see lesions yet. We had a low leaf spot infection on June 3 and again on June 8. The wetting period was too short on June 9 for another leaf spot infection period.  

Growers need to be managing for this disease as unlike scab, leaf spot is always present in the orchard and can cause infection throughout the season. Captan is an excellent material for leaf spot, and 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, and 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 phytotoxicity to leaves. Flint Extra, a strobilurin, is also excellent against leaf spot.  

Pest report 

American plum borer. We caught an average of 3.7 moths this week, which is down slightly from last week where we caught an average of 8.3 moths. 

Lesser peachtree borer. We caught lesser peachtree borer for the third week, and the numbers jumped up a lot from last week. We caught an average of 30 moths per trap compared to three moths last week. In the past, we would target trunk sprays to overlap American plum borer and lesser peachtree borer, and even greater peachtree borer to maximize the trunk sprays. We are much more limited in the material we can use for spraying trunks. Check with your processors about spraying certain materials. 

Black stem borer. We caught four black stem borers this week. 

San Jose scale. We caught males for the first time this week. We caught very few, 1.3 per trap, and this catch is an indicator that this pest in on the move.  

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 12-14 mm, and plum curculio will oviposit into this fruit. Growers have reported plum curculio stings in cherry fruit, and we have oviposition damage in sweet cherries at the Northwest Michigan Horticulture Research Center.  

These insects are out and active, particularly with this warm weather. This pest can sneak up on cherry growers whose main focus is SWD, 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 at this time because Avaunt needs to be ingested, and neonics are anti-feedants.  

Codling moth. This pest has increased a lot since last week. We did have some warmer evenings, so codling moth activity likely increased with the warm weather. This pest flies at dusk. We caught 68 moths in our apple block near the woods at the Northwest Michigan Horticulture Research Center. The other two traps only had seven and two moths. Setting a biofix might be hard for this pest with the swings in temperatures and the fluctuating codling moth activity. The first date of sustained captures of males in traps is used to set a biofix for the codling moth degree-day model, which uses accumulated degree-days for predicting key pest life stages and helps target the proper timing for management. The action threshold for codling moth is an accumulation of five to seven moths in any one trap.  

We caught codling moth at the Northwest Michigan Horticulture Research Center two weeks in a row, so we are going to set our biofix for June 3. If we set biofix for June 3, we are at the timing for a material targeting eggs, such as Rimon, as we are at 100 GDD from biofix. Rimon (novaluron) is an insect growth regular that has strong ovicidal activity, thus codling moth egg laying is the optimal timing for this material. Rimon applied at codling moth biofix plus 100 GDD also provides excellent control of obliquebanded leafroller, and suppression of plum curculio (sublethal effects on subsequent generation).  

Growers that are not trapping on their own farm can use the biofix we set here at the Northwest Michigan Horticulture Research Center. Many growers use the traditional timing for controlling codling moth larvae. Most insecticides registered for use against codling moth are aimed at killing larvae, and thus are typically applied beginning at 250 GDD post biofix. Depending on the weather, we should be near 250 GDD post biofix next week. “Codling moth management options for Michigan apples” is a good article on codling moth codling moth 

Thinning 

Be cautious about thinning this year with some damage from April cold weather in various orchards. We also may have some pollination issues with the cool weather. Lastly, there has been a variety of stages of fruitlet development with the cool temperatures then the random warmups. Growers should know what is going to stick on their trees by now. As mentioned above, we are at 15mm in size in both Gala and Honeycrisp, so we still have a little time to thin before the fruit gets too big. This cool weather is not going to help with thinning. The trees are also showing an excess in carbohydrates, which is also going to make thinning more difficult. The model is recommending increasing the thinner rates by 30% because the fruit will be more difficult to thin. 

According to the MSU Apple Thinning Guide, thinning sensitivity is low at petal fall, greatest at 10 mm, and then quickly becomes insensitive at 25 mm. Warm and cloudy conditions will promote thinning, and under cool and sunny weather, thinners will be less effective. However, growers that have fruit that is over 15 mm need to get a thinner on if they have not thinned in the past. The weather conditions are important for thinning, and it is not the day of thinner application but the following three to five days that are key to good thinning.  

Michigan State University has worked with the new thinner, Accede. Accede, a chemical thinner based on the naturally-occurring compound ACC (the immediate precursor to ethylene). Accede is primarily intended for later thinning treatments (fruit size 15-18 mm) when earlier chemical thinners like 6-BA (MaxCel) and NAA are no longer as effective. It works best as part of a season-long thinning program, not as a standalone solution. Michigan trials have shown it to be particularly effective in the "rescue" thinning window, when fruitlets are approximately 20 mm in diameter. Accede can be used when the king fruit's average size ranges from 8-25 mm, and growers should apply Accede at a rate of 23-46 fluid ounces per acre. Best results are achieved under slow drying conditions (e.g., early morning, at night). Accede should be used in combination with earlier thinning applications as part of a complete program for optimal thinning. Do not apply as a tank mix with other thinning products.