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

• Apples

  • Growth stage update

  • Article: Bocking comfrey orchard understory cover (Site specific strategies; video included)

• Grapes

  • Growth stage update

  • Hedging and skirting grapes

  • Early-veraison is the next chance for petiole testing

Apples

Growth stage update:  Fruit development (average 70-90% final size)

Images: Apples are approaching 70-90% of their full size at Sekapp Orchard (Rochester, MN), depending on the variety. Varieties in photos from left to right, top: McIntosh, Gala, First Kiss; bottom: Honeycrisp, Kindercrisp, and Zestar!. 

Apples are continuing to size up as the season progresses. General management during this time focuses on preventing summer rots and sooty blotch and flyspeck. Insect pest management should continue as needed, based on trap catches. For example, apple maggot is estimated to be at 50% adult emergence in most parts of Minnesota (see below), and growers should continue to renew the tanglefoot coating on apple maggot sphere traps after insecticide applications to stay informed of when the next application is needed. 

Image: Apple maggot degree day model as of July 22, 2026, created by Anthony Hanson from the University of Minnesota. 

While Japanese beetles are less likely to directly feed on fruits, they can still cause damage to trees by feeding on the foliage and, similar to other crops, the more beetles that are feeding and breeding, the more volatiles are released that attract beetles. Management for Japanese beetles, apple maggot, codling moth, and other pests during this time can be found in the Midwest Fruit Pest Management guide starting on page 39. 

Images: Japanese beetles can aggregate on apple trees and cause foliar damage, while occasionally damaging apples that are already injured, such as wildlife damage.

Article: Comfrey as a ground cover in apple orchards (grower highlight)

For orchards that follow organic management practices, or are USDA certified organic, finding ways to manage ground vegetation without using conventional herbicides is important. What works well for one orchard may not work for another, based on the orchard layout, density, and visual preferences. 

This week’s article covers the use of the Bocking series of comfrey as an under-the-tree cover crop, which has been a preferred method by Alternative Roots Farm due to its senescing nature that leads the plant to collapse several times each year and cover the ground around it, shading out nearby vegetation. 

For more information and a short video, check out this week’s article:

Article: Bocking comfrey orchard understory cover (Site specific strategies; video included)

Grapes

Growth stage update: E-L stage 33 (berries still hard and green)

Images: Grapes are getting closer to transitioning into veraison at Four Daughter’s Vineyard located in Spring Green, MN. Varieties in these photos include Marquette (upper left), Edelweiss (upper right), Brianna (lower left), and Frontenac Gris (lower right). 

As we reach closer to the end of July, vineyards located in central and southern Minnesota will start to see a number of varieties enter veraison within the next two weeks. Veraison is the start of the third stage of fruit growth when the berries begin to soften, acidity begins to decline, and sugars begin to build. 

Chart: Grape berry development phases from berry formation into ripening, which happens after veraison begins. Chart created by J. Kennedy in 2002. 

At this stage, grape clusters have grown out of their vulnerability to berry infections like black rot, powdery mildew, and downy mildew, while leaves and rachises may still be vulnerable to infection. 

In regards to insect pests, for sites that have detected Japanese beetles through trapping or observation, management is recommended to prevent egg laying in the vineyard and extensive canopy damage. Keep in mind that Japanese beetles tend to have an aggregative effect where beetle feeding and breeding attracts more beetles.

Hedging and skirting grapes

Images: A tractor-mounted hedger can help speed up the process of hedging commercially grown grapes.

Hedging and skirting are two terms related to summer, or green pruning for grapes. Upright systems, like Vertical Shoot Positioning (VSP) have their shoots trimmed at the top of the trellis and are hedged, while downward positioned systems are trimmed, or skirted just above the ground.

Grapevines typically require around 12 leaves to ripen each cluster, which should be kept in mind during summer pruning; however, as long as the grape clusters are ripening well (i.e., berry enlargement and, most importantly, fruit coloration and sugar development), this is a sign that the vine is healthy and capable of ripening its fruit. 

Very small vineyards can easily hedge grapevines using hand shears or electric shears. Electric shears designed for vineyards are usually propped up on a pole and come with a harness. These can also be used for skirting High Cordon vines.

As the size of a vineyard grows, or for very vigorous vineyards, purchasing a tractor-mounted hedger can be of great help. This week, I visited Hannah Hanlon who is the winemaker and vineyard manager for Four Daughters Vineyard while she was hedging the vineyard. 

Their vineyard utilizes a Rineri hydraulic hedge trimmer, which has the ability to change its angle, but cannot be positioned to trim the top of the vines. When hedging is delayed, however, the shoots will be long enough to hang over the canopy, and the hedger does a good job trimming. This can actually be helpful, as hedging too early can lead to excess growth and the need to hedge multiple times in one season. 

While the process for hedging is much simpler and faster using a tractor-mounted hedger, Hannah still recommends hedging vineyards, small or large, in small chunks of time as it does require the driver to be alert, and stay in a straight line, and avoid wires and posts. With this specific model, it is also helpful to stay on top of greasing the hedger.  

Are you looking for more support with grape production at your vineyard? Check out the UMN online grape course for more information on production ($15.00). 

Online course: Growing cold climate grapes: Vineyard management

Early-veraison is the next chance for petiole testing

With veraison being just around the corner for many regions in southern Minnesota, it’s a good time to make a plan and make sure you have supplies for petiole testing. Petiole nutritional analysis gives a snapshot of the nutrient profile within a plant at a given time, and can be helpful for vineyards and nutrient management. It can be used in comparison to soil nutrition levels to track plant health in general, and is more often used to diagnose nutritional deficiencies when symptoms appear. 

Because plant nutrient (e.g., nitrogen, calcium, zinc) levels change based on a plant’s demands, there is not one baseline nutrient profile for reference throughout the whole growing season. Instead, references exist for specific times of the year for a given plant. Bloom is the first opportunity for sampling and veraison is the second. 

How to take samples at veraison:

• Samples should consist of 75-100 petioles from 25-50 representative grapevines— this could be a specific vineyard region or variety. It also helps to sample vines that are the same age and grown on similar soil. To avoid sampling bias, avoid taking more than 2 leaves per grapevine.

• Depending on the lab you are submitting a sample to, either collect petioles from the youngest fully mature leaf, or, collect the 5th to 7th fully mature leaf from the shoot tip.*

• Remove the leaf blade. 

• Place samples into a paper bag that is labeled to help you keep organized, especially when taking more than one sample. Staple the bag.

• Determine which nutrients you want analyzed. This could include nitrogen (N), phosphorus (P), potassium (K), and other nutrients like calcium (Ca), manganese (Mn), zinc (Zn), boron (B), iron (Fe), and copper (Cu). If you are seeing issues with fruit set, zinc (Zn) and boron (B) can be especially helpful to look at. 

• Fill out paperwork and send your samples to the lab of your choice. The University of Minnesota does offer petiole analysis. Feel welcome to reach out to the UMN Fruit Program at wimm0035@umn.edu for questions about your results.  

For more information about foliar and petiole nutritional analysis, check out this article:

Test don’t guess: Is foliar nutritional analysis right for your fruit crops this growing season?

Resources:

Tissue and soil nutrient testing for cold climate grapes (UMN webpage)

Taking a foliar sample: Vineyards and orchards (UMN instructional YouTube video)

*Note: Our UMN video recommends finding the youngest fully mature leaf as a sample itself, while other protocols recommend collecting leaves at the 5-7 nodes below the last mature leaf. Check with your lab to see which protocol is recommended. 

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.