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

• Apples 

  • Growth stage update: Nearing harvest season for early-season apples

  • Article: Organic apple orchard practices highlight in SW Michigan: Third Leaf Farm

• Grapes

  • Article: Measuring fruit ripeness

  • Article: Occasional insect pests that attack damaged grapes in Minnesota vineyards

• Blueberries

  • Nutrition: Iron deficiency

Apples

Growth stage update: Nearing harvest season for early-season apples 

Images: Outer-canopy apples are gaining color for these cultivars grown on central leader, freestanding trees. Top images, left to right: Gala, Honeycrisp, McIntosh. Bottom images, left to right: KinderKrisp, First Kiss, Wealthy. Not all of these cultivars are early ripening.

This week, we’ve been receiving some cooler nights and mornings, which is beneficial for Minnesota apple production as cooler temperatures during the night can impact fruit anthocyanins and help improve apple color. This is one of the reasons why cooler climates are great for Honeycrisp production, an apple that is considered more of a bicolored apple rather than a red apple, which makes production challenging in warmer regions. This has also led to sport cultivars of Honeycrisp like Royal Red Honeycrisp, and the breeding of many Honeycrisp descendants (ex. Cosmic Crisp). 

As you near harvest, keep in mind pre-harvest intervals for products like stop-drop sprays and pesticides. In regard to obtaining a quality harvest, know which apple varieties in your orchard ripen evenly, and which ones may need several harvest passes to get quality fruit. If you’re planning on storing fruit for a long period of time, remember that less-ripe fruit will generally store longer. Make a plan for the fruit you harvest based on your postharvest and market plans. 

Article: Organic apple orchard practices highlight in SW Michigan: Third Leaf Farm 

Images: Using concrete posts is one way to follow the USDA Organic regulation against using treated wooden posts. 

Are you interested in learning more about organic practices you can incorporate into your orchard management? This week’s article shares some highlights from a field day at Third Leaf Farm that happened in July of this year. Third Leaf Farm is USDA certified organic and focuses on regenerative practices like understory orchard mowing. They have also been incorporating concrete posts into their orchard rows as an alternative to conventionally treated wood posts, which are restricted under USDA organic production standards. 

To learn more about these topics, check out the whole article using the link below. 

Article: Organic apple orchard practices highlight in SW Michigan: Third Leaf Farm

Grapes

Article: Measuring fruit ripeness

Quantifying how ripe grapes are can make a big difference to harvesting high-quality fruit for grape production. 

It’s important to harvest wine grapes when the grapes are on average at a sugar and acidity level that is desired for winemaking because grapes do not continue to ripen after being picked. They are non-climacteric, which is different from bananas that will fully ripen after being picked unripe. 

But it’s not just about wine grapes. Bringing underripe table grapes to the market can impact consumer perception, as underripe grapes can be overly tart, lack desirable flavor profiles and coloration.

As grapes ripen on the vine, sugar levels increase while acid levels go down and the pH rises. When evaluating berries in the vineyard, measuring soluble solids (e.g., estimate of sugar concentrations measured in degrees Brix) with a refractometer and the pH (roughly estimated with pH strips, or more precisely with a pH meter) are fairly simple to do, while titratable acidity is usually best done indoors with a titrator.  

To learn more about this process, check out this week’s article on measuring fruit ripeness:

Article: Monitor grape cluster ripening for a quality harvest this year

Article: Occasional insect pests that attack damaged grapes in Minnesota vineyards

Grapes generally have fewer insect pest issues than apples, but when it gets close to harvest time, there are a few insects that become pests, especially when grapes are damaged from hail, splitting, or birds. These include the multicolored Asian lady beetle, social wasps, and fruit flies, which are associated with sour rot. 

Check out this week’s article to continue reading about this topic.

Article: Occasional insect pests that attack damaged grapes in Minnesota vineyards

Blueberries

Nutrition: Iron deficiency

Image: Interveinal chlorosis with a light yellow coloring is a classic sign of iron deficiency as seen in this blueberry plant. 

Blueberries are well known for their unique requirement for acidic soils (pH ideally between 4.5 – 5.2). When the soil pH is out of balance and is higher than their preferred range, root growth becomes restricted and access to nutrients like iron decreases. Iron deficiency can show up as interveinal chlorosis with a light yellowish background color. Shrubs can also have smaller leaves, and be stunted overall. 

Correcting this condition often involves adjusting the soil pH, but growers should also take note of their irrigation pH and alkalinity, as irrigation water with high alkalinity can cause the soil pH to creep up eventually. The most common way to lower soil pH involves using elemental sulfur. 

If you’re planning to do this on your farm, it’s going to be most helpful to start by doing a soil test on your site where blueberries are already growing or will be planted. Both the soil pH and soil type will inform how many pounds per acre are needed for lowering the pH, where loam and silt loam soils tend to need much more elemental sulfur than sand or sandy loam type soils.

The above table is sourced from the UMN resource, “Nutrient Management for Fruit and Vegetable Farms.”

It’s important to keep in mind that it can take several months for the sulfur to react with soil, which is why it’s best to apply it before the year you decide to plant blueberries. It can also be helpful to retest your soil pH around 3–4 months after making an application. 

For growers who are interested in using iron sulfate instead of elemental sulfur, it’s recommended to multiply the original sulfur rate by 7 to determine the total amount of iron sulfate needed per acre, which can then be applied as a split application. 

If you’re already planning to apply nitrogen to your site, the UMN guide, “Nutrient Management for Fruit and Vegetable Crops in Minnesota” also mentions that ammonium sulfate can help lower pH levels when used (do not overapply beyond current nitrogen needs). 

Finally, there is a limit to when it is practical to try to lower your soil pH. For example, if your soil pH is above 7, it’s generally challenging to try to lower the pH. Instead, it might be more helpful to focus on growing a different fruit crop, such as honeyberries, saskatoons (serviceberries), or currants. 

To learn more about acidifying irrigation water, check the resources section below. 

Article resources: 

• Nutrient Management for Fruit and Vegetable Crops in Minnesota (UMN)

• Treating irrigation water (Texas A&M)

• Acidifying soil (Oregon State University)

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 within the UMN Extension system.