UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

• Apples

  • Apple scab cultural management: Encouraging leaf decomposition

  • Article: Apple storage disorders and recommendations for four UMN varieties

  • Did you see moldy core in your apples this year?

• Grapes

  • Harvest efficiency: Another case for strategic canopy management

• Raspberries
  • Article: Managing raspberry cane borers this fall

This week’s update concludes the fruit update series for 2026. Each year comes with its challenges and 2026 was no exception with episodes of spring frost, continued drought conditions, and severe weather in various parts of the state. As you continue growing your fruit crops, it is with great hope that the content provided in this newsletter has provided you with some support. 

As always, if there is any topic that you would like to see discussed more in the future, please reach out and let me know by email or by taking our annual survey. Based on demand, the newsletter has a large focus on apples and grapes, but other fruit crops matter just as much. If there’s something you’re not seeing here, please let us know!

UMN Fruit and Veg News Annual Survey

Our newsletter is only a success because of readers like you, and we greatly appreciate your feedback.

Until next year, we’ll continue to release a number of single articles on various fruit-related topics like pruning and other relevant subjects. 

With fruitful regards,

Madeline Kay Wimmer 

UMN Extension Fruit Production Educator

Apple scab cultural management: Encouraging leaf decomposition

Image: A graphic based on Ben Fontana’s illustration of how he approaches leaf blowing and mowing at Apple Jack Orchard located in Delano, Minnesota. Graphic recreation by Madeline Wimmer, UMN Extension.

Much effort is put toward managing apple scab primary infections during the spring when overwintering fruiting bodies release spores during rain events, especially when temperatures are warm and in an optimal range. 

As long as these initial spores are prevented from creating new asexual spores on leaves and fruits, the amount of inoculum, or overwintering spores present by the end of the year is greatly reduced. For growers who do experience secondary infections, however, or those who want to be extra sanitary in the orchard, encouraging leaf decomposition during the fall can be helpful. This is because it encourages overwintering fruiting bodies to degrade and decrease how many sexual, or primary spores released during the following spring. 

Leaf decomposition occurs as infected leaves weather from the environment and microorganisms break down plant material and fruiting bodies along with it. This process can be encouraged by stimulating microbes through spray applications of 40 pounds of urea (46-0-0) in 100 gallons of water (1). 

The other way leaf decomposition is encouraged is by increasing the total surface area of the leaf litter by mowing the leaves. This is sometimes easier said than done, especially for larger orchards where leaves can get stuck underneath trees.

For instance, Ben Fontana, orchard manager at Apple Jack Orchards, has taken the time to improve this method by using a leaf blower to force leaves into the aisles between tree rows. This works best when the direction of the wind can be used to their advantage by blowing the leaves with the wind. 

A combination of both methods, encouraging microbial growth and making it easier for them to consume the leaf litter, can work well for orchards that have the time and resources to be more thorough. 

Resources:

Peter, Kari A. Apple diseases - Apple scab. PennState Extension. 2023.

Article: Apple storage disorders and recommendations for four UMN varieties

Images: An example of a larger storage facility that has the capacity to store apples using controlled atmosphere conditions where low oxygen levels increase fruit longevity (left). An apple showing symptoms of bitter pit, which can start in the orchard and worsen during storage (right). 

The majority of apple sales in Minnesota are direct-to-consumer sales through farm stores, U-pick, and farmers markets. This often means that end-of-season sales finish up in late fall or before the new year, making for a relatively short storage duration. 

However, for growers who do plan to extend their sales into winter markets, proper storage becomes a bigger topic of focus. For example, apples that are stored for longer periods of time are generally harvested at an earlier stage of maturity based on the starch iodine test and other indicators.

Longer storage requires careful attention to aspects like how quickly the apples are cooled down and storage conditions like temperature and humidity. When the conditions aren’t right, a number of storage disorders can result, like bitter pit, soft scald, or symptoms from dehydration.

To learn more about this topic, check out this week’s article below.

Article: Apple storage disorders and recommendations for UMN varieties

Did you see moldy core in your apples this year?

Image: Moldy core observed on First Kiss at an orchard in Minnesota. 

You may have seen a few apples coloring faster than others, and, upon slicing them open, found noticeable mold within the apple core surrounding the seeds. While there existed what looked like a codling moth exit hole, no frass was apparent and the actual mold within the core was a sign that the apple was infected with moldy core.  

Moldy core is a condition caused by fungi that enter apples through the calyx end. It is more likely to happen during years when the weather was dry earlier in the summer, followed by heavier rainfall in the late summer, and with low fruit set. 

Moldy core is unlikely to spread to the apple flesh, although, when it does, it can lead to dry core rot. Infected are unmarketable, and can be a cause of concern for consumers, and that alone may be enough to encourage growers to keep an eye out for them and remove infected apples when possible.  

While the current literature on moldy core management does not have concrete evidence for specific spray programs to prevent it, there are some varieties, like First Kiss, that are more susceptible than others.

Resources: 

Apple disease: Moldy core (PennState Extension)

Harvest efficiency: Another case for strategic canopy management

Images: Brianna vines and clusters just before harvest. Trained onto Vertical Shoot Positioning (VSP) with adequate cluster exposure makes for an easy harvest. 

Richard Smart was an Australian researcher who did a number of foundational studies analyzing how sunlight affects grapes. He was known for saying things like, if you can’t see the grapes, neither can the sun. Excess sunlight in some regions of the world can be problematic for grape production, but in the Upper Midwest, the goal is usually trying to get more sunlight into the canopy through proper row spacing, basal and lower lateral shoot thinning, and shoot positioning. This can really help with fruit quality, but there’s another reason cluster exposure and canopy management matter: for hand harvesting grapes. 

The way clusters hang in a canopy and how easily they can be seen impacts how quickly someone can locate, grab, and harvest a cluster, especially with people who are new to harvesting. While there are so many other tasks always happening around a vineyard and winery throughout the season, coming out to the vineyard to thin shoots early on (aiming for 6–8 shoots per linear foot), pull leaves and lateral shoots after fruit set, and taking time to do some brisk combing for high-wire cordons and shoot tucking for vertical shoot positioned vines can really pay off. 

Harvesters who cannot easily see clusters, need to duck under canopies to get to deeper-positioned fruits, reach their hands around impeding leaves, or pull off tendrils from nearby creeping shoots will take longer to harvest and may end up missing more clusters overall. 

Investing in canopy management has long-term implications, too, as the fruiting buds for next year’s crop develops this year. Sun exposure can increase fruitfulness overall. And, as a final note, how easy it is to harvest grapes goes beyond canopy management as training systems themselves influence the cluster zone height and depth (think 3D systems like GDC and Lyre, which can create deeper canopies). Additionally, which tools are used and how well they are maintained can also make a big difference. 

Raspberries

Article: Managing raspberry cane borers this fall

Raspberry cane borers are an occasional pest for raspberry growers. If you've seen the tips of your brambles wilting, it could be a sign that adult borers laid eggs this year. Cane borers impact fruiting for fall-, or primocane-bearing raspberries, and cane health for summer-, or floricane-bearing raspberries. Because borers take two seasons to emerge as adults, it is to your advantage to prune back wilted tips in the summer and the fall. If this has been an issue for you this year and you haven't done it yet, there is still time. 

To learn more about raspberry cane borers, their life cycle, and management, check out this week's article.

Article: Managing raspberry cane borers this fall

Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or are from the UMN Extension system.