Article written by Madeline Wimmer, UMN Extension Fruit Production Educator
- Apple
- Growth stage and pest management update: Fruit enlargement (3-6cm)
- San Jose scale and apple maggot info
- Rapid or Sudden Apple Decline
- Grapes
- Growth stage and pest management update: Fruit set entering stage II
- What causes poor fruit set
- Boron and Zinc deficiency info
- Article: Black rot
- June-bearing strawberries
- End-of-season reflection from Afton Orchard
- Plan for end of season bed renovation
- Honeyberries
- Article: Honeyberries (Haskap) as a U-Pick Crop for Minnesota
Apples
Growth stage and pest management update: Fruit enlargement
Images: Fruits in SE Minnesota are reaching between 3-6cm, with Zestar! being further ahead in development. The varieties in the above photos are Gala (3-3.5cm), First Kiss (3-4cm), McIntosh (4-5cm), and Zestar! (5.5-7).
Apples in SE Minnesota are approaching roughly half their size at harvest, which is between stages 74 and 75 for the BBCH growth stage chart. Trees are also approaching the time of year when shoots begin to set their terminal buds, which means shoot growth slows down for the year.
Diseases
With the assumption that full bloom occurred around May 5th this past year, we’re about 7 weeks past bloom this week, which places us around the timing of third and summer cover sprays for pest management. Recall that during most years the majority of overwintering apple scab spores finish discharging 1-2 weeks after petal fall, meaning orchards with low scab pressure this year, and good spring coverage can reduce their program.
Insect pests
San Jose scale
Images; 1) An apple branch wrapped with reversed electrical tape within a population of San Jose scale (Diaspidiotus perniciosus), 2) using a jeweler’s lens to look closely, and 3) a magnified view of San Jose scale crawlers, which are the small yellow specks mixed among a cluster of scale coverings. Images taken by Kate Scapanski, UMN apple researcher at the UMN Horticulture Research Center (HRC.)
We’re approaching the time period when growers can begin to monitor for San Jose scale juveniles, also known as crawlers. In 2024, the apple crew at the UMN Horticultural Research Center (HRC) trapped crawlers during the week of June 27th, but their development and activity are dependent on degree day accumulations in regards to when they will emerge this year.
Cornell’s NEWA program has an application for San Jose scales where an orchard can get predictions of pest stage based on trapping of the first generation (first male catch) using pheromone traps specific to San Jose scale. Adult male emergence usually occurs around late May through June in Minnesota, and crawlers tend to emerge around 600-700 degree days (base 51° F) after the first male is caught.
Apple maggot
Apple maggot emergence continues to move north as we progress into the season and degree days continue to accumulate. For readers who have been following this specific map made by Anthony Hanson of UMN Extension, you’ll note that this map includes adult emergence and gravid female emergence. This is important because egg laying does not happen immediately after adults emerge. The gravid female emergence refers to female flies that are mature enough to lay their eggs in fruit, which is beginning in southern regions of Minnesota and is closer to when egg laying will begin.
Recall that most management for apple maggot will begin 7-10 days after an orchard has reached the threshold of one adult catch per trap per week on unbaited traps or five adults per trap per week on baited traps. Continue management by following label instructions until they are no longer present in the orchard. Remember to keep monitoring and refreshing your traps to keep track of adult populations.
For more information on apple maggot management refer to this article, published earlier in the season:
Preparing for apple maggot management in 2026 (organic and conventional practices)
RAD/SAD dieback symptoms tend to begin midsummer, unlike winter injury, which happens earlier in the season. And while RAD/SAD is commonly observed in the Mid-Atlantic and Northwest apple growing regions, it's useful to be aware of in contrast to winter injury dieback as reports of RAD/SAD in the Upper Midwest have become more common in recent years.
Maintaining irrigation when drought conditions are present can help trees enter dormancy in better condition. However, many factors beyond management practices can still put trees at risk of winter injury, including a tree's depth of dormancy, regional weather patterns, and site specific conditions like soil type, ground cover, and overall topography and surroundings (i.e., risks from cold traps from wooded edges or low spots).
Apple trees and other fruit crops do go through sequential stages of dormancy: acclimation, deep dormancy (endodormancy), followed by a light dormancy (ecodormancy) and deacclimation. Still, trees can also become slightly more or less hardy based on winter temperatures, depending on the timing and the duration of the temperature exposure.
References:
Images: Three grape varieties, Itasca (upper left), Marquette (upper right), and Brianna (lower center), in SE Minnesota are continuing to enlarge as they get closer to stage II development.
Grapes are continuing to develop in SE Minnesota, which coincides with growth stages 29-31 for the modified E-L Growth Chart and the Midwest Fruit Pest Management Guide section, “Grape Shatter to Veraison.” Unless your vineyard has a particular insect pest issue that you know of, this is still a quiet period for insect pest management before Japanese beetles emerge.
Recall that most management for apple maggot will begin 7-10 days after an orchard has reached the threshold of one adult catch per trap per week on unbaited traps or five adults per trap per week on baited traps. Continue management by following label instructions until they are no longer present in the orchard. Remember to keep monitoring and refreshing your traps to keep track of adult populations.
For more information on apple maggot management refer to this article, published earlier in the season:
Preparing for apple maggot management in 2026 (organic and conventional practices)
Rapid, or Sudden Apple Decline (RAD/SAD)
Two weeks ago, the newsletter covered information on dogwood borer and the connection to rapid or sudden apple decline (RAD/SAD). Here is more background knowledge to understand the underlying condition. Based on recent research, RAD/SAD usually relates to the graft union and rootstock shank, and may involve interactions between the rootstock and scion, along with external factors like freeze and thaw cycles, and potential pathogen involvement.RAD/SAD dieback symptoms tend to begin midsummer, unlike winter injury, which happens earlier in the season. And while RAD/SAD is commonly observed in the Mid-Atlantic and Northwest apple growing regions, it's useful to be aware of in contrast to winter injury dieback as reports of RAD/SAD in the Upper Midwest have become more common in recent years.
Maintaining irrigation when drought conditions are present can help trees enter dormancy in better condition. However, many factors beyond management practices can still put trees at risk of winter injury, including a tree's depth of dormancy, regional weather patterns, and site specific conditions like soil type, ground cover, and overall topography and surroundings (i.e., risks from cold traps from wooded edges or low spots).
Apple trees and other fruit crops do go through sequential stages of dormancy: acclimation, deep dormancy (endodormancy), followed by a light dormancy (ecodormancy) and deacclimation. Still, trees can also become slightly more or less hardy based on winter temperatures, depending on the timing and the duration of the temperature exposure.
References:
- Rapid or sudden apple decline (RAD/SAD) - Webinar (UW-Madison and UMN Extension)
- Midwest Fruit Pest Management Guide
Grapes
Growth stage and pest management update: Fruit set entering stage II
Images: Three grape varieties, Itasca (upper left), Marquette (upper right), and Brianna (lower center), in SE Minnesota are continuing to enlarge as they get closer to stage II development.
Grapes are continuing to develop in SE Minnesota, which coincides with growth stages 29-31 for the modified E-L Growth Chart and the Midwest Fruit Pest Management Guide section, “Grape Shatter to Veraison.” Unless your vineyard has a particular insect pest issue that you know of, this is still a quiet period for insect pest management before Japanese beetles emerge.
It is still important to proactively manage grape diseases during this growth stage, especially in regions that are experiencing rainfall, keeping in mind that grape berries can become more resistant to some diseases like black rot and downy mildew as they further enlarge. Disease management recommendations can be accessed for this growth stage starting on page 149 of the Midwest Fruit Pest Management Guide.
The term shatter refers to the dropping or loss of unfertilized berries. This happens about 7-10 days after full bloom, and is normal for this growth stage. A healthy vine should retain around 30-50% of its blossoms/berries during this stage, although some varieties may retain more. Anything less than that is considered abnormal. Later in the season, the “hen and chicks” cluster appearance can become more apparent, where a cluster has some very small green berries and others that continue normal development and ripening.
Poor fruit set can relate to environmental conditions as well as grapevine nutrient deficiencies, specifically zinc and boron. To determine if nutrients are the cause for poor fruit set, a petiole test should be taken, for which the next window is early veraison.
When considering boron applications, foliar can be a good option as soil applications need to be done with caution to prevent toxicity, which can be challenging to correct.
The term shatter refers to the dropping or loss of unfertilized berries. This happens about 7-10 days after full bloom, and is normal for this growth stage. A healthy vine should retain around 30-50% of its blossoms/berries during this stage, although some varieties may retain more. Anything less than that is considered abnormal. Later in the season, the “hen and chicks” cluster appearance can become more apparent, where a cluster has some very small green berries and others that continue normal development and ripening.
Poor fruit set can relate to environmental conditions as well as grapevine nutrient deficiencies, specifically zinc and boron. To determine if nutrients are the cause for poor fruit set, a petiole test should be taken, for which the next window is early veraison.
Boron deficiency
Additional symptoms for boron deficiency include stunted root and shoot growth, a bushy or excessibely branched canopy. Additionally, petioles can be short and thick, and shoot internodes can have a zig zag appearance. Boron is important for cell wall health in addition to pollen tube elongation and ovary health. Leaf symptoms can show streaks of chlorosis (yellowing) followed by necrosis (cell death) that looks brown.When considering boron applications, foliar can be a good option as soil applications need to be done with caution to prevent toxicity, which can be challenging to correct.
Zinc deficiency
When zinc is deficient, leaves tend to become a pale green color, leaf size may be stunted, and the leaf shape itself can become deformed at the borders. Internodes tend to be shorter with zinc being deficient as well, in addition to poor fruit set. When evaluating zinc levels within a leaf sample, it is helpful to also have a soil sample to refer to since excess phosphorus can immobilize zinc in the soil.Article: Black rot
Black rot is a fungal disease caused by the pathogen Guignardia bidwellii. Infections can affect grape leaves and shoots during early parts of the season, which can lead to fruit infections later on. To learn more about the impacts of black rot and management recommendations, refer to this week’s article below.Article: Black rot on grapes (Guignardia bidwellii)
June-bearing strawberries
End-of-season reflection from Afton Orchard
When I spoke with Ryan Femling of Afton Orchard this week on the topic of how the season went for June-bearing strawberries, he mentioned that growers throughout the state had varying experiences: no one was in the same boat. Spurts of hot days in April seemed to speed up development for his fields at Afton Orchard, followed by a couple of points at the end of April and beginning of May when the daily minimum temperature reached around 20-21 F. For earlier varieties, this seemed to freeze out some of the king blossoms, while secondaries were primarily affected in later-bearing varieties.Afton Orchard has been growing strawberries and other fruit crops for around 37 years. They’ve had frost issues before, including some issues last year, and a memorable year of frost in 2012. They pre-pick strawberries and host U-Pick at their farm with an additional concession stand that offers a variety of strawberry goods, including strawberry shakes, waffles, donuts, and ice cream.
Afton Orchard grows a number of strawberries that are suitable for his sandy loam textured soil. They currently grow some early bearing varieties like Honeyeye and Brunswick, along with some mid-season bearing varieties, including Jewel and Yambu. They avoid planting varieties that bear very late in the season to avoid issues with spotted wing drosophila (SWD).
Ryan mentioned that the frost their farm experienced impacted some yield this year, but wasn’t major. It may have impacted the U-Pick experience by slowing down how long it took pickers to fill up their containers.
Was your farm impacted by frost this year? Feel welcome to reach out to share your experience by emailing wimm0035@umn.edu, or filling out our fruit crop reporting form.
Plan for end of season bed renovation
Strawberry bed renovation is an important part of maintaining June-bearing strawberry productivity and involves a few steps that can help increase fruit set for the following year and maintain plant health.Mowing
Bed renovation involves mowing over the bed at a height that goes above the strawberry crowns, which removes old leaves and exposes the crowns to more sunlight and encourages stronger fruiting bud development. If there was disease development in leaves, mowing can also help encourage their decomposition. Mowing can also decrease spotted wing drosophila favorability, which can be helpful for farms that will have late-season strawberries, or other susceptible fruit crops fruiting after the renovation finishes.
Weeding and narrowing rows
This is also a good time to weed since the plant canopies will be reduced. Mowing can help remove runners, but using a cultivator of some type to narrow the rows is also helpful for removing runners for fields that have already established matted rows.
Fertilizing and irrigating
Additionally, renovation best practices recommend fertilizing strawberries and irrigating them to keep the plants healthy. Fertilizer recommendations vary based on whether the fields are in their establishment or bearing years. Check out our UMN Extension webpage for specific information on fertilizer amounts per nutrient (see below). Irrigation should continue throughout the summer, especially into August and early September when fruit set is occurring.
For more information, check out our UMN Extension webpage and this video below, which is also available on the UMN Extension Small Farms YouTube channel.
Video: Renovating Strawberry Beds (UMN Extension 4 min 39 sec)
Bed renovation involves mowing over the bed at a height that goes above the strawberry crowns, which removes old leaves and exposes the crowns to more sunlight and encourages stronger fruiting bud development. If there was disease development in leaves, mowing can also help encourage their decomposition. Mowing can also decrease spotted wing drosophila favorability, which can be helpful for farms that will have late-season strawberries, or other susceptible fruit crops fruiting after the renovation finishes.
Weeding and narrowing rows
This is also a good time to weed since the plant canopies will be reduced. Mowing can help remove runners, but using a cultivator of some type to narrow the rows is also helpful for removing runners for fields that have already established matted rows.
Fertilizing and irrigating
Additionally, renovation best practices recommend fertilizing strawberries and irrigating them to keep the plants healthy. Fertilizer recommendations vary based on whether the fields are in their establishment or bearing years. Check out our UMN Extension webpage for specific information on fertilizer amounts per nutrient (see below). Irrigation should continue throughout the summer, especially into August and early September when fruit set is occurring.
For more information, check out our UMN Extension webpage and this video below, which is also available on the UMN Extension Small Farms YouTube channel.
Video: Renovating Strawberry Beds (UMN Extension 4 min 39 sec)
Honeyberries
Article: Honeyberries (Haskap) as a U-Pick Crop for Minnesota
Image: Honeyberries maintain their shape and quality for a longer period of time when picked by hand.
The UMN Fruit and Veg Newsletter has been covering topics on honeyberry production this year and following Haskap Minnesota, located near Stillwater, MN. Right now, varieties like Boreal Beast and Boreal Beauty are at peak harvest. There are many different honeyberry varieties available to grow currently with a spectrum of growth characteristics, harvest windows, and fruit characteristics. Both Boreal Beast and Boreal Beauty were bred by Bob Bohrs from the University of Saskatchewan for their upright growth habit and uniform ripening, and are well-suited for mechanical harvesting, but also suitable for fresh eating.
Honeyberry U.S.A. is one farm that has offered U-Pick honeyberries for a number of seasons, and this is the first year that Haskap Minnesota is opening for U-Pick.
Check out this week’s article to learn more about the consideration for U-Pick honeyberries:
Honeyberries (Haskap) as a U-Pick Crop for Minnesota
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.
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