Fruit update - July 23, 2025

Article by Madeline Wimmer-UMN Extension Educator, Fruit Production

• General fruit :
• About: The winsome fly and Japanese beetles
• Pollinator installations and support
• Apples:
• Growth update: Beginning of ripening
• Grapes:
• Symptom check: Black rot on grape berries
• Plums:
• Russeting on fruits

General fruit:

About: The winsome fly and Japanese beetles

Image: Japanese beetle adults will continue to feed as winsome fly eggs are laid on their thorax (middle body segment). The larval feeding eventually kills the Japanese beetle, which disrupts egg-laying in female beetles.

While you’re out monitoring for and managing Japanese beetles this year, you might take note if you see any beetles with one or more white dots on their green thorax. These are eggs of the winsome fly (Istocheta aldrichi), a tachinid fly that is a parasitoid* of Japanese beetles.

It only takes a few days after eggs are laid for a larva to hatch and begin feeding and developing through its larval stages. This damage does not cause instant death, but slowly deteriorates the Japanese beetle's abilities until it dies. Around this time, the larvae pupate within the beetle and overwinter until the following June.

The increase in observations of winsome fly eggs on Japanese beetles in Minnesota is an example of natural biocontrol and one of several ecological developments that has led to some natural control for Japanese beetles.

For more information on the winsome fly, check out the following resource:

UMN webpage: The Winsome Fly, Istocheta aldrichi: A unique biocontrol agent for Japanese Beetle in Minnesota

Interested in putting parasitoids you’re seeing on the map? Check out the UMN citizen science survey:

Survey: Winsome fly & Japanese beetles

*Parasites feed from hosts, requiring that the host stay alive, whereas parasitoids like the winsome fly will typically lay eggs that consume the host from within until it dies.

About: Pollinator installations and support

Images: Pollinator resources often recommend planting three species of pollinator friendly plants, specific to your crop and region, for each bloom period (early, mid-season, late).

This week’s newsletter release includes an article about supporting pollinators by installing on-farm pollinator-friendly plantings. The planning process to create pollinator habitat is most successful when it’s centered around crop-specific pollination goals, and being aware of other site-specific factors like soil type and USDA growing zone to direct plant selection and site preparation choices.


To learn more about pollinator-friendly habitat installations, check out this week’s UMN Fruit and Veg News article:


Article: Planning for a pollinator-friendly habitat installation

New: UMN pollinator planning guide for fruit growers

If you’re at the early stages of planning a pollinator habitat installation, taking some time to define your pollinator goals and needs for success is a good starting point.

The University of Minnesota recently published a short guide that walks you through this.

Create space for some unstructured time, make a cup of something warm, and step into your planning brain—you’ll want to think creatively as well as practically during this process.

 

UMN pollinator management planning guide: https://z.umn.edu/pollinator_plan

Apples

Growth stage update: Beginning of ripening

Image: Zestar!® apples beginning to show color at Sekapp Orchard in Olmsted County (Zone 5a).

Apples in southeast Minnesota are entering into the beginning stages of ripening with some color becoming visible on a few apples positioned on the exterior parts of the canopy. Zestar!® is one early-ripening variety that was showing its signature red striping pattern, as exemplified in the above photo.

During this stage of development, management for summer rots and superficial diseases like sooty blotch and flyspeck can be prioritized, especially in regions that have been experiencing high humidity and rain. Similarly, insect pests are site specific and are best managed when monitored through scouting and trapping.

Support for conventional pesticide programs throughout this time can be found on page 36 of the Midwest Fruit Pest Management Guide under, “Apple third and summer covers - Diseases.”

Grapes

Symptom check: Black rot on grape berries

Images: Two different infected clusters with berries in various stages of black rot development.

Black rot, caused by the pathogen Guignardia bidwellii, becomes more visibly noticeable as berries pass through stage II of growth. A purple color begins to develop on the berries before they completely change color and eventually shrivel and dessicate into mummies, where spore-holding fruiting bodies are formed.

Fruit infection is one route for the pathogen to overwinter, along with any lesions formed on canes. Removing infected clusters during bad infection years can be helpful, especially when there are a large number of berries infected on a cluster. Small vineyards may be able to practice shelling, or removing individual infected berries out of the cluster, and destroying them.

As with many fungal diseases, chemical management strategies for black rot need to be proactive. Grape clusters are most vulnerable to infection around bloom, which is a critical management period. For conventional guidance related to black rot chemical management, refer to page 169 of the Midwest Fruit Pest Management Guide under, “Grape shatter to veraison (berry coloring) - Diseases.”

While certain fungicides have some kickback action, they are not curative, and do not eliminate the problem of existing inoculum in the vineyard. Black rot management improves greatly when infected tissues are removed in addition to chemical management.

References and further reading:
Black rot (Cornell Cooperative Extension)

Plums

About: Russet scab

Images: Fruit from the plum variety, Gracious, is ripening at the UMN Horticultural Research Center with some fruits showing signs of russet scab, seen here as the brown coloration on the fruit skins.

I have observed plum russetting in several orchard settings this season. Russetting is a fruit skin abnormality where the cuticle has been disrupted with micro-cracks. To the untrained eye, it might look like the beginning stages of a particular fruit rot, but it is mostly associated with environmental conditions like rain during bloom, and high winds leading fruits to rub on one another.

Russets can decrease fruit marketability for customers looking for unblemished fruits. While these fruits may not hold up in storage as well as non-russeted fruits, they are safe to eat.

Based on conditions shortly after bloom this year, it is very possible this resulted from high winds. In cases like this, some cultural approaches include opening up the canopy through pruning to reduce fruit injury from wind-blown branches, leaves, and neighboring fruit.

Thank you to our farm and agricultural professional partners for contributions to the UMN Fruit Update series. Unless otherwise credited, photos were taken by Madeline Wimmer or sourced from the UMN Extension system.

This article may be shared for educational purposes with attribution to the University of Minnesota Extension and author(s). For other uses, please contact UMN Extension for permission.