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

• Apples

  • Article: Tracking apple maggot populations and considerations for organic management

  • Article: Training young free-standing apple trees

• Grapes    

  • Deer damage and management

  • Downy mildew: Identifying oil spots and management

  • Replacing trellis in-line posts 

• Day-neutral strawberries

  • Article: Organic Day-neutral Strawberry Insecticide Efficacy for Tarnished Plant Bug

• General fruit

  • Drought monitor update

  • UMN Extension Fruit Crop Reporting Tool

Apples

Article: Tracking apple maggot populations and considerations for organic management

Image: Apple maggot adults are attracted to red sticky ball traps, which can be more effective when combined with a lure on the inside. 

Apple maggot is a pest (Rhagoletis pomonella) that is less common in commercial orchards, but still relevant for many, and can lead to fruit tunneling, distortion, and drop in severe cases when left unaddressed. In Minnesota, we are still early with regards to when apple maggot will emerge, which means this is a good time to take inventory of traps and products used for management.  

Continue reading this article here…

Tracking apple maggot populations and considerations for organic management

Article: Training young free-standing apple trees

Images: Clothes pins can spread branches early, when shoots are still green and malleable.

Apple tree height and the number of years to fruiting (precocity) depend largely on the rootstock an apple variety is grafted onto. Establishment is the process of caring for a tree after planting to maintain its health, while training relates to encouraging a specific tree shape for the benefit of its health and production. 

This article goes into concepts of pruning and branch manipulation for free-standing tree establishment. While pruning is done during the dormant season, it is being discussed in this article because it is important for tree establishment. 

Continue reading this article here…

Training young free-standing apple trees

Grapes  

Deer damage and management

Image: Deer damage can lead to a clean heading cut to young shoots when they are tender. 

Deer can be an issue in vineyards earlier in the season, depending on a vineyard location and populations present. They tend to prefer tender shoots. Even if there is no damage to grape clusters, this can still impact shoot growth and lead to early branching. 

For small vineyards, where deer pressure is high, a deer fence can be helpful to exclude them. Fence options include 96-inch-high fences (which can be amended with a secondary mesh fence), or electrical fences that deliver a minimum of 5,000 volts.

Other management options that can be implemented for short-term needs and when deer pressure is low include deer repellent such as putrescent egg solids and thiram. Some home remedies like human hair and soaps have weaker evidence, although I recall the Peninsular Agriculture Research Station, located in Door County, WI, known for using cashmere scented mini soaps on their trees in previous years. 

One other option is an outdoor motion sensor app like YoLink, which alerts the user when deer trigger the motion sensor. This can be helpful for tracking activity, but might be more suited for growers that easily fall back to sleep, since much deer activity occurs at night. 

The Minnesota Department of Natural Resources offers a cost-share program (Wildlife Damage Management Program) for growers who have previously experienced deer damage to assist in costs related to deer fence installation and other management approaches. For more information, contact your local wildlife area office: Wildlife area office directory based on county. 

Downy mildew: Identifying oil spots and management

Oil spots are most commonly associated with early downy mildew infection in grapes and are helpful to scout for in the vineyard. Downy mildew is caused by the pathogen Plasmopara viticola and is one of the main diseases to target during early-season management. As the disease progresses, white spores can be seen on the underside of the leaves, in contrast to powdery mildew, which shows up on the top of the leaf surface. 

Eventually, these spots will turn brown and infections can spread to grape clusters, which are generally susceptible to infections until around 3 weeks after bloom. For less severe incidences of infection, growers can remove infected clusters in hopes the remaining healthy clusters escape. Grape floral clusters and rachis are additionally susceptible to infection.

Because the pathogen over winters on the ground on infected leaves, it can be helpful to rake dropped leaves into the vineyard aisles and mow them to encourage decomposition, especially for sites with histories of severe infection. 

Chemical management is discussed starting on page 138 of the Midwest Fruit Pest Management Guide (budbreak through prebloom).  Copper products have traditionally been a backbone of many organic downy mildew management programs, some of which are listed in the guide. Lifegard is also listed in the guide as a biopesticide option for downy, while Howler is another product being researched at Cornell University as a management option in rotation with other products for control—both products being organic approved. 

Resources:

Downy mildew (Michigan State University Extension: Integrated Pest Management)

Replacing trellis in-line posts 

Images: A nearly-twenty-year-old wooden trellis post that has weakened and broken at the base.

Wooden trellis posts are one option for trellis construction and are sometimes chosen due to aesthetics, cost, and ease of modifying and attaching hardware for hanging wires. Most wooden posts sold are treated, which work well for conventional vineyards, however, organic growers should take note of which treatment products are allowable under certification guidelines as many are prohibited.

The longevity of wooden posts is highly influenced by whether they are treated and which treatment products are used, but their installation and maintenance also matter. Wooden posts should either be level to the ground or slightly mounded to prevent water from pooling around the base, which can lead to rot. 

In the case of the broken post in the above photo, this post is nearly 20 years old, but ended up breaking at the base and needs to be replaced. At Salem Glen Winery, Dustin Eber, who has been making wine since 2007, will plan to replace the post by first drilling a hook into the ground-embedded portion of the post and pulling it out with a chain. The next step is to install and secure a new post and redo the wire attachments for guiding the fruiting and training wires. 

Day-neutral strawberries

Article: Organic Day-neutral Strawberry Insecticide Efficacy for Tarnished Plant Bug

Tarnished plant bug (TPB, Ligus lineolaris) is a strawberry pest to manage for Midwest growers, especially for organic production systems. TPB feeds on developing strawberry seeds (achenes) as well as the surround parts of the young strawberry buds, flowers, and fruit. 

Their damage leads to "catfacing" deformations (apical seediness), which reduces strawberry yield and marketability. Since day-neutral strawberries continuously bear fruit throughout the season, TPB damage can be exceptionally devastating when populations are not well-managed.

In the summer of 2024, an insecticide spray trial was conducted at the University of Minnesota Agricultural Experiment Station in Saint Paul, Minnesota. Three OMRI-listed insecticides were applied to organic day-neutral strawberries individually and in rotation to assess their efficacy for managing TPB.

Continue reading this article here…

Organic Day-neutral Strawberry Insecticide Efficacy for Tarnished Plant Bug

General fruit

Drought monitor update

Image: Current drought conditions (05/28) on the left Minnesota map as compared to drought conditions earlier this month (05/07). 

Drought conditions are increasing as compared to the beginning of the month as abnormally dry conditions continue to spread throughout the Southeast, Southwest, and parts of central Minnesota, while moderate drought conditions are expanding in Northcentral Minnesota. The current 7 day, total precipitation forecast map shows a range between 0.01-1.00 inches, with more accumulations reported for Southwestern Minnesota while the Southeast corner will remain dry, which may lead to expanding drought conditions.    

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 aspects 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.