Article written by Madeline Wimmer, UMN Extension Fruit Production Educator.
Apples
Growth stage and pest management update: Petal fall
Article: Considerations for fruit thinning for normal and cold damage years
Fruit thinning at petal fall
Article: European red mite (ERM; occasional pest) + Beneficial insect highlight: Predatory mites
Grapes
Canopy management: Shoot thinning (video link included)
Berries
Article: Spotted Wing Drosophila parasitoid found in Minnesota
Video: Honeyberries/haskap: New video highlighting grower practices
UMN Extension Fruit Crop Reporting Tool
Apples
Growth stage and pest management update: Petal fall
Images: Late stage petal fall seen in Zestar! (left) and early stage petal fall in Gala (right) correlates with bloom timing for these two varieties. Photos taken at Sekapp Orchard of Rochester, MN, on May 14, 2026.
After full bloom, once pollination window has ended, those apple fruitlets that were successfully pollinated will begin to develop as their petals senesce and fall, beginning with the earliest blooming flower.
The petal fall growth stage can be a good time for growers to focus horticulturally on tasks like post-bloom chemical thinning (see section below) and pest management for key insect pests and diseases like apple scab.
Insect pest and disease management:
Plum curculio (Conotrachelus nenuphar) is one of the major apple insect pests that show up at or before petal fall, often starting with tree rows located closer to wooded edges where plum curculio adults emerge (see next section below for more information).
Continue to check traps and scout for codling moth eggs, but note that this period is usually too early for management with pesticide applications.
For orchards with a history of issues with European Red Mite (ERM) or Oriental Fruit Moth (OFM), which are less common in Minnesota orchards, this becomes a relevant monitoring and management period.
This is additionally a period of time when dogwood borer mating occurs (less common), and when leaf rollers and spotted-tentiform leaf miners are active.
Apple scab primary infections caused by spores from overwintering fruiting bodies continue to be a risk at this growth stage until 100% of spores are discharged. For more information about conventional control measures for apple scab, refer to the Midwest Fruit Pest Management Guide.
Article: Considerations for fruit thinning for normal and cold damage years (UW-Madison article)
Are you concerned about cold damage on blossoms for the 2026 season and how to adjust your fruit thinning method this year? Learn what damaged blossoms look like in our previous fruit update on April 30, 2026, and check out the article below by Fruit Specialist, Amaya Atucha, out of the UW-Madison Fruit Program.
Read the full article here:
Thinning Apple Trees After a Frost Event: What to Do and When
Fruit thinning at petal fall
Image: Varieties like Honeycrisp and Haralson that have biennial bearing tendencies benefit from early-season fruit thinning done during bloom or petal fall. The above photo shows two rows of apple trees, both in bloom, with low return bloom on the right side.
Early-season fruit thinning is especially helpful for apple varieties like Honeycrisp, McIntosh, and Haralson, which are known for biennial bearing with low return bloom occurring every other year. If you’re in a northern region and interested in bloom thinning, check out our article, “Bloom thinning apples and understanding the pollen tube growth model.” Petal fall is the next opportunity to fruit thin.
For orchards that are concerned about substantial blossom damage from cold weather this year, however, it’s best to wait until later and learn more about adjusting your thinning methods with the article posted in the section above.
The products available to use for petal fall thinning include hormonal (i.e., plant growth regulator) products like NAA (e.g., Fruitone N, PoMaxa, or Refine), or 6BA (e.g., Maxcel), which interrupt natural development processes causing developing fruitlets to abscise/drop.
Carbaryl (e.g., Sevin and Sevin XLR+) is a different product available for use, which acts as a mild thinner through mild phototoxicity. It’s important to recognize that carbaryl is a broad spectrum insecticide that can harm pollinators and should be used with that consideration in mind for application timing.
It’s possible for growers to combine multiple thinning products, or add adjuvants when tank mixing, to increase product efficacy. Thinning will also be more effective earlier when products are applied before apples reach approximately 12 mm in size.
If it’s your first time thinning fruit, it might be reassuring to hear that many growers think that they have overthinned initially. Recall that only one fruit is needed per fruiting spur, or tip, and a healthy distance between fruits—from one spur to the next—is about 4-6 inches. Thus, thinning may appear dramatic when first practiced until later in the season when the fruit load is easier to see due to an increase in fruit size.
Article: European red mite (ERM; occasional pest) + Beneficial insect highlight: Predatory mites
For orchards where European red mite (ERM) is an issue, populations can quickly build when left unmanaged, however, predatory mites play an important role in keeping populations under control.
To learn more about ERM, check out this week’s article:
European red mite (ERM; occasional pest) + Beneficial insect highlight: Predatory mites
Grapes
Canopy management: Shoot thinning
Images: Shoots on new canes should be spaced around a fist distance apart and rarely need shoot thinning unless secondary shoots emerge with the primary shoots (right photo).
Early-season shoot growth can happen very quickly during this time, especially with warmer weather in the forecast. Grape shoots are very tender when they first emerge and become more stiff as they reach about one-foot in length. Before then, they can easily be removed by hand, decreasing the amount of time dedicated to shoot thinning.
Cold climate grapes are generally recommended to bear between 6-8 shoots per linear foot of canopy, while shoots on new canes should be spaced approximately a fist-width apart to establish good spur spacing.
While pruning is the first step to limiting the number of shoots per linear foot of canopy, there are several reasons to return for early shoot thinning. Having a balanced number of shoots in a given amount of canopy helps bring vines into balance and prevent overcropping. It additionally allows for good airflow and sunlight throughout the canopy.
During pruning, it’s common to miss buds and underprune, which leads to a number of shoot options to select from when thinning out unnecessary shoots. Additionally, growers may need to take out secondary shoots that simultaneously emerge with primary shoots for some grape varieties.
The amount of shoot thinning done should be enough to do a good job, but is not a hard science that requires a lot of thought and input. Begin the process when shoots are young and tender, especially for vigorous, dense vines. Waiting too long can increase the effort it takes to remove shoots.
Watch a video featuring John Thull, UMN Vineyard Manager teach about shoot thinning:
Berries
Spotted wing drosophila parasitoid found in Minnesota
Spotted wing drosophila (SWD) has been one of the most devastating pests to raspberries and other berry crops in the U.S. for the past 10+ years. Part of its advantage comes from being an invasive species, which means it did not have many natural predators and parasitoids, allowing it to be a serious problem.
Much research has been done to learn more about SWD and management options (check out a previous webinar on SWD research and management here), including research on parasitoids like Ganaspis brasiliensis and Leptopilina japonica. These parasitoids kill their host by laying eggs either in the SWD larva or eggs, which then hatch and eat the pest from the inside.
An ideal parasitoid only targets the pest at hand, and sometimes can start to establish in various climates by surviving winter conditions and other ecological conditions. Recently, Leptopilina japonica was found in Minnesota, which is a positive indication for the natural control of SWD in our region.
To learn more about this, check out an article from the UMN Roger’s lab in this week’s Fruit and Veg News update:
Spotted-wing drosophila parasitoid detected in Minnesota: what growers should know
Honeyberries/haskap: New video highlighting grower practices
Image: Honeyberries from the 2025 growing season harvest at Haskap Minnesota. Photo by Jolene Brink, UMN Communications.
Interested in learning more about honeyberry/haskap production? Check out a new 9-minute video on the UMN Small Farms YouTube channel highlighting George Terwey of Haskap Minnesota farm, located near Stillwater, MN. If you have more questions after watching the video, reach out and let us know so we can best support you!
Video: Honeyberry/Haskap Farming 101
UMN Extension Fruit Crop Reporting Tool
Interested in sharing anything about the fruit crops on your farm? Feel free to share observations about diseases, pest management, or other production issues using our new UMN Extension Fruit Crop Observation Report tool. If you have a question you want addressed in a future update article, you can include that in your report.
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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