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Weekly Fruit Update 6/4/2020

Author: Annie Klodd, Extension Educator for Fruit Production

If you're seeing interesting things in your fields, insects and diseases, or just want to share photos, we'd love to hear from you! As always, don't hesitate to reach out with questions and pictures. We're still here for technical assistance over the phone, via text, or via email.

Fruit questions go to Annie:
Vegetable questions go to me Natalie:
Food safety questions go to Annalisa:

Strawberry Fruit Set

Strawberries at bloom and fruit set in White Bear Lake on June 1, 2020. Photo: Annie Klodd.
I scout every Monday at Pine Tree Apple Orchard in White Bear Lake. At this location, strawberry bloom was at 10% on Monday, May 25. Fruit set was beginning by Monday, June 1, with stands in full bloom. This puts the beginning of strawberry season at June 20.

Some mild leaf injury was observed following the mid-May freeze event, but very few blossoms were impacted. In general, I am aware that frost damage may have occurred at a couple of locations, but have not observed or heard about much damage at all. For the most part, flower buds had not yet emerged at the time of the mid-May freeze event. 

Critical Time for Strawberry Disease Management

Bloom is a critical time to control diseases on strawberries, as botrytis gray mold and anthracnose are active now. Remember that just because we cannot see the symptoms, that does not mean the fungi aren't actively infecting. Good disease control prior to infection is necessary in many cases. Additionally, the warm temperatures and rain we have been experiencing are ideal conditions for disease development. Please refer to this article for organic and conventional recommendations for controlling strawberry diseases at bloom. 

Saturday Frost Event in Northern Minnesota

Farms near Brainerd and Duluth have reported an unexpected frost event this weekend. This frost event seems to have occurred in pockets rather than covering a vast area of the state. Fruit crops were, of course, in vulnerable fruit stages at that point. Crops including blueberries and strawberries may have been impacted. Growers who experienced frost should walk the field and examine flower buds and developing fruit to evaluate the extent of damage. The critical freeze injury temperature for developing blueberry fruit, as well as strawberry blossoms, is 28 degrees F. This varies somewhat depending on the cold hardiness of the variety. If damaged, the blueberry fruit will develop a water-soaked appearance before shriveling and dropping.

Time for Apple Fruit Thinning

Haralson fruitlets on June 1, 2020. Photo: Annie Klodd

In White Bear Lake on Monday, June 1, fruitlets were at the following approximate size ranges:
  • Zestar: 8-11 mm
  • SweeTango: 5-10 mm
  • Honeycrisp: 5-8 mm
  • Haralson: 5-10 mm
Growers should be evaluating crop load and applying chemical thinners at this time. Thinning decisions such as product and number of applications should factor in current crop load, variety, tree vigor, and weather. Please refer to our two podcast episodes on fruit thinning here, for product recommendations and considerations. 

What's Killing My Kale Season 2 episode 22: Thinning Techniques for Apple Trees Through the Season

Grape shoot thinning & bud injury

Marquette shoots of varying stages in Mankato, MN on May 29, 2020. Photo: Annie Klodd

We are getting toward the very end of the window for shoot thinning. Shoots should be thinned when they are between 4-11 inches long. Once they grow a foot long, they begin to adhere better to the spurs and become more difficult to pull off without creating injury to the spurs. Shoot thinning creates better air flow through the canopy, for disease control and spray penetration, and supports better fruit development by balancing the vine's energy between the fruit and canopy.

A number of vineyards have reported vines that failed to break bud. This may be caused by a variety of events including the November 2019 cold snap, compromised vine health from the 2019 polar vortex, or the May 2020 frost event. Please see this article for more information.

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