Madeline Wimmer- UMN Fruit Production Extension Educator
Images: Apple petal fall begins with the earliest blooming flowers, after which successfully pollinated fruits will begin to develop. The tool on the right is an apple thinning template that measures fruitlet circumferences to determine effectiveness of apple post-bloom chemical thinners. Right photo by UMN Researcher, Kate Scapanski.
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 marks a time for growers to focus horticulturally on tasks like post-bloom chemical thinning and pest management for key insect pests and diseases like apple scab. For more information on fruit thinning after bloom, refer to last week’s fruit update apple blurb, “Apple fruit thinning continued (post-bloom)”
Insect pest and disease management:
Image: Chart showing daily and cumulative ascospore discharge history and projection for the UMN Horticulture Research Center from April 8th until May 24th, 2025. Spores that cause apple scab are released from overwintering fruiting bodies during wet, warm conditions until 100% discharge has occurred.
Are you still in bloom in your orchard? Check out last week’s article highlighting information about bloom:
Article: UMN Fruit and Veg News - May 14, 2025
Plum curculio (Conotrachelus nenuphar) is a common pest of apples and other tree fruits in the Upper Midwest. During petal fall, plum curculio adults can begin entering the orchard when temperatures are consistently above 60F and start ovipositing, or laying eggs underneath the fruit skin as soon as fruits reach 5mm.
Image: Most cold climate grapes are trained onto two-dimensional trellises. There are a number of features and materials that can vary in the final construction, and labeled parts show the main parts needed. Functions of these parts are described in the article linked below.
Grape phylloxera has multiple generations per growing season. The first generation, known as crawlers, are mobile and emerge in the spring from mother eggs on the trunk and cordons and migrate to the newest grape foliage, which can lead to 40-50 galls per leaf. Thus, the University of Minnesota recommends managing the crawlers as the most critical management stage, especially when growing more vulnerable cultivars like Frontenac.
For vineyards with an extensive history dealing with grape phylloxera, consider timing insecticide applications as soon as early galls are detected.
For more information on management, refer to the Midwest Fruit Pest Management Guide starting on page 161.
Resources:
Tips for managing grape phylloxera (University of Minnesota)
Leafhoppers in high tunnel raspberry production
Images: An unidentified species of light-colored leafhoppers found in a high tunnel stand of raspberries with resulting damage shown in the above photos.
Spotted wing drosophila (SWD) is the most dramatically impactful insect pest to affect raspberries, but there are a number of other insect pests that occasionally also show up. These include Japanese beetles, sap beetles, leaf rollers, spider mites, and leafhoppers, shown in the photos above on raspberry plants that were growing in a high tunnel in southern Minnesota.
Leafhoppers are an indirect raspberry pest, meaning that they do not directly harm raspberry fruits like SWD and sap beetles. Instead, leafhoppers are a sucking and piercing pest that reduce the ability for leaves to photosynthesize and produce energy for the developing berries, like thrips and mites, which also feed by piercing and sucking.
Leafhoppers are a unique insect in that their populations cannot overwinter in the Upper Midwest, and come into the region each year traveling on wind currents. In addition to the damage they cause, leafhoppers can also transmit diseases like rubus stunt disease. General management information for leafhoppers is provided in the Midwest Fruit Pest Management Guide.
Resources:
Raspberry trellises carry less weight than trellis for some fruit crops like grapes, but overtime end posts can still cave in without good reinforcement. There are a number of trellising options for raspberries, most commonly including V-angled end posts and crossbar trellis posts to extend the containment wire. Similar to trellises for other fruit crops, a well-designed raspberry trellis requires the end posts to be pulled back to maintain a counter force to the other trellis end post(s). The most common way this is done is by anchoring the endpost into the ground using either wire or cable that goes between the end post(s) and an anchor. Some raspberry trellises use in-line posts that go between the two end posts, but many do not, which can put more weight on end-posts.
Follow this video to see one way to reinforce end posts and the guiding wire. Supplies used include spiral anchors, wire rope clips, hook-and-eye turnbuckles, and cable, which were supplies that were available on site that day. The wire rope clips were used to secure the endpost cable, as well as the containment cables that hold the raspberry canes. The hook-and-eye turnbuckles used were fully extended before installing, allowing for future tensioning as time goes on. Anchors are screwed into the ground and provide anchorage for the anchoring cable attached to the endpost.
The above video was filmed and produced by Madeline Wimmer in partnership with Renewing the Countryside’s Farm Buds trip to D& S Gardens, a farm that grows fall-bearing, or primocane-bearing raspberries, among other specialty crops.
- Apples
- Growth stage update: Petal fall
- Pest highlight: Plum curculio
- Grapes
- Growth stage update: Pre-bloom
- Article: Understanding trellis "anatomy" for cold climate grape establishment
- Shoot tucking VSP vines
- Pest highlight: Grape phylloxera
- Raspberries
- Leafhoppers in high tunnel raspberry production.
- Video: Reinforcing raspberry trellis end posts on a small scale production stand.
Apples
Growth stage update: Petal fall
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 marks a time for growers to focus horticulturally on tasks like post-bloom chemical thinning and pest management for key insect pests and diseases like apple scab. For more information on fruit thinning after bloom, refer to last week’s fruit update apple blurb, “Apple fruit thinning continued (post-bloom)”
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). Keep in mind that their activity slows down with cool temperatures like many Minnesota regions have experienced this week.
- 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. Right now, the UMN Horticulture Research Center is projected to reach around 88% cumulative ascospore discharge this week by the Cornell NEWA apple scab model. For more information about conventional control measures for apple scab, refer to the Midwest Fruit Pest Management Guide starting on page 27.
Are you still in bloom in your orchard? Check out last week’s article highlighting information about bloom:
Article: UMN Fruit and Veg News - May 14, 2025
Pest highlight: Plum curculio (common pest)
Image: Plum curculio (Conotrachelus nenuphar) pressure from previous years should be taken into account when thinking about scouting this year.
Apples tend to be an unsuitable environment for plum curculio development as eggs and larvae are usually crushed and killed as the apple develops. While this is good news for apple growers, it does not remove the initial plum curculio scar left by female egg laying adults, which often looks like a raised crescent moon. The scars are a minor blemish and are safe to eat, however this affects fruit appearance and marketability. Fruit can additionally look somewhat dimpled or deformed.
Growers can scout for plum curculios daily after petal fall since this is the most critical management period for plum curculio. Plum curculio adults are dark brown weevil beetles that are about ¼ inch long, with light patches and four humps located on their back (wing covers). Scout by looking for slit-like scars on fruitlets, especially on orchard perimeter rows. Beating trays can also be used to check for plum curculios within the tree canopies.
Orchards that have had heavier plum curculio pressure during previous growing seasons may begin scouting earlier as plum curculio can show up as early as bloom. It’s additionally recommended to check earlier blooming varieties that will reach petal fall first.
Refer to the Midwest Fruit Pest Management Guide for options in regards to management (pyganic is often used for management in organic production). Plum curculio adults are active and management is typically needed until 308 DD (base 50 °F) have accumulated after petal fall, marking the end of peak egg-laying activity. Degree days can be monitored through a model like Cornell’s NEWA plum curculio model.
Apple curculio:
While plum curculio is a major pest of apples, there also exists a lesser-known pest commonly known as the apple curculio (Anthonomus quadrigibbus) that can become problematic for some orchards. Apple curculio differs from plum curculio by the ovipositing wound they leave on fruits after egg laying, and those eggs/larvae that survive will continue to pupate within fallen apple fruits. This makes removing fallen fruits from the orchard floor especially important for managing apple curculios.
For more information on apple curculios in apple production, check out the article below:
Article: Apple curculio: A lesser-known orchard pest
As grapevines continue to grow past their initial leaf out phase, the floral bud clusters become visible. Shoots at this phase are still tender and easy to thin by hand. This continues to be an important time for fungicide programs to protect against infections from early-season diseases.
Growers can scout for plum curculios daily after petal fall since this is the most critical management period for plum curculio. Plum curculio adults are dark brown weevil beetles that are about ¼ inch long, with light patches and four humps located on their back (wing covers). Scout by looking for slit-like scars on fruitlets, especially on orchard perimeter rows. Beating trays can also be used to check for plum curculios within the tree canopies.
Orchards that have had heavier plum curculio pressure during previous growing seasons may begin scouting earlier as plum curculio can show up as early as bloom. It’s additionally recommended to check earlier blooming varieties that will reach petal fall first.
Refer to the Midwest Fruit Pest Management Guide for options in regards to management (pyganic is often used for management in organic production). Plum curculio adults are active and management is typically needed until 308 DD (base 50 °F) have accumulated after petal fall, marking the end of peak egg-laying activity. Degree days can be monitored through a model like Cornell’s NEWA plum curculio model.
Apple curculio:
While plum curculio is a major pest of apples, there also exists a lesser-known pest commonly known as the apple curculio (Anthonomus quadrigibbus) that can become problematic for some orchards. Apple curculio differs from plum curculio by the ovipositing wound they leave on fruits after egg laying, and those eggs/larvae that survive will continue to pupate within fallen apple fruits. This makes removing fallen fruits from the orchard floor especially important for managing apple curculios.
For more information on apple curculios in apple production, check out the article below:
Article: Apple curculio: A lesser-known orchard pest
Grapes
Growth stage update: Pre-bloom shoot growth (continued)
Images: Photos of grapevine shoot growth on cold hardy variety, Itasca. Photo taken at a vineyard in Olmsted County, MN (Zone 5a; 05/21/25).
For more information about thinning and early-season grapevine diseases, refer to previous Fruit Updates:
- Fruit Update - May 14, 2025 (information on shoot thinning)
- Fruit Update - April 30, 2025 (infographic and information on early-season diseases and management)
Article: Understanding trellis "anatomy" for cold climate grape establishment
Image: Most cold climate grapes are trained onto two-dimensional trellises. There are a number of features and materials that can vary in the final construction, and labeled parts show the main parts needed. Functions of these parts are described in the article linked below.
Are you getting ready to install a new trellis? Planning out trellis construction takes knowing which trellis design, tools, and supplies you'll need to create something solid that will last for years.
Take time to learn more about different parts that make a trellis work in this week's article:
Grower participatory survey: Are you seeing delayed or failed budbreak in your vineyard this year?
Image: Vineyard block showing cold climate Marquette wine grapes, many of which have had delayed, or no bud break yet this year. Brianna grapes in this vineyard block appeared to experience more even bud break, and the Itasca (planted in a separate block) broke bud more evenly and grew typically.
This year, we’ve been receiving a number of reports of failed bud break, meaning buds have not begun to grow. This type of loss has been concerning for those affected.
The past year brought on a number of different factors that contributed to vine stress, including the frequent early-season rainfall, followed by a dry period with various degrees of drought, a warm fall, and a winter with very little snow cover compared to previous years, on average. These factors all coming together could have had a number of effects on vines’ vascular systems, their acclimation into dormancy, and ability to withstand further stress from freezing and thawing, or extreme cold.
If you are seeing either irregular bud break, or no budbreak from certain vines, wait to see if latent buds sprout from the trunk or cordons, or suckering begins at the base of the vine. Because most cold climate grape varieties (i.e., Frontenac, Marquette, Petite Pearl) are not grafted, it’s ok to use suckers to retrain trunks and this ability, and is a great advantage to their survivability in northern regions.
Grower survey: Grapevines failing to break bud in 2025
The University of Minnesota wants to hear from vineyards observing failed bud break. This will help us better understand the scope and degree of the issue, and support our ability to deliver future education that will better help growers like you.
2025 Grape Growers Bud Break Survey
Images: Vertical Shoot Positioned (VSP) vines work well for hand harvested vineyards based on the fruiting zone height and positioning of clusters. Some grape varieties that have downward/procumbent/trailing growth are less conducive to this training (shoots can “slip” out of catch wires) in early years before spurs have been established.
Vertical Shoot Position (VSP) grapevines are trained to have their shoots guided into an upright position where they will continue to grow until they reach the top of the trellis. The main fruiting wire is positioned lower than a downward system like High Cordon, usually around three feet tall. If the top of the trellis is 6-7 feet tall, this allows for 3-4 feet of canopy, or between 10-20 grape leaves, depending on shoot height, internode length, and hedging practices.
It’s a common rule of thumb that it takes around 12 fully developed leaves to adequately ripen a cluster of grapes, which again varies based on the energy demands of the cluster: How large are the berries? How many berries are there per cluster?
Trellises designed to support the VSP training system have a series of either single wires or catch wires to train this current season’s shoots upwards. These wires are usually a thinner gauge than fruiting wires.
Single wires:
Because many cold climate wine grapes exhibit semi-upright growth, they need help being guided upwards. Single wires require growers to manually attach shoots that did not make contact with their tendrils. This can be done with a tool known as a tapener, a handheld tying tool, which can be time consuming, but is an option for single wires.
Catch wires:
Alternatively, trellises can have double wires, or catch wires that act as a basket to contain shoots as they grow upright. This training is usually much less time consuming and can be modified by making wires moveable in a way that they can be moved to hoop shoots into the middle of the catchwire basket, sections at a time. Growers can also go out when shoots are just barely reaching the first pair of catch wires, and walk along a row while tucking in groups of shoots with your arm.
If you’re using catch wires, don’t wait too long to tuck your shoots! It can become increasingly difficult to tuck in shoots that have grown far beyond the first set of wires, especially if it becomes more stiff through development.
Image: A grape leaf showing early signs of Grape phylloxera (Dactylosphaera vitifoliae) galls, circled in yellow. Photo taken at the UMN Horticultural Research Center, near Chaska, Minnesota (Zone 5a; photo taken by John Thull- UMN HRC Vineyard Manager).
Grape phylloxera (Dactylosphaera vitifoliae) is an insect pest that was historically known for devastating the wine industry after Vitis vinifera grapes were first brought to the U.S. It can cause damage to both the roots and foliage of grapes, but the cold climate grapes grown in Minnesota, which contain genetics from wild American grapes like Vitis riparia, are resistant to root damage and are only susceptible to foliar damage.
The past year brought on a number of different factors that contributed to vine stress, including the frequent early-season rainfall, followed by a dry period with various degrees of drought, a warm fall, and a winter with very little snow cover compared to previous years, on average. These factors all coming together could have had a number of effects on vines’ vascular systems, their acclimation into dormancy, and ability to withstand further stress from freezing and thawing, or extreme cold.
If you are seeing either irregular bud break, or no budbreak from certain vines, wait to see if latent buds sprout from the trunk or cordons, or suckering begins at the base of the vine. Because most cold climate grape varieties (i.e., Frontenac, Marquette, Petite Pearl) are not grafted, it’s ok to use suckers to retrain trunks and this ability, and is a great advantage to their survivability in northern regions.
Grower survey: Grapevines failing to break bud in 2025
The University of Minnesota wants to hear from vineyards observing failed bud break. This will help us better understand the scope and degree of the issue, and support our ability to deliver future education that will better help growers like you.
2025 Grape Growers Bud Break Survey
Vineyard task: Tucking or securing upright growing shoots (Vertical Shoot Positioning)
Vertical Shoot Position (VSP) grapevines are trained to have their shoots guided into an upright position where they will continue to grow until they reach the top of the trellis. The main fruiting wire is positioned lower than a downward system like High Cordon, usually around three feet tall. If the top of the trellis is 6-7 feet tall, this allows for 3-4 feet of canopy, or between 10-20 grape leaves, depending on shoot height, internode length, and hedging practices.
It’s a common rule of thumb that it takes around 12 fully developed leaves to adequately ripen a cluster of grapes, which again varies based on the energy demands of the cluster: How large are the berries? How many berries are there per cluster?
Trellises designed to support the VSP training system have a series of either single wires or catch wires to train this current season’s shoots upwards. These wires are usually a thinner gauge than fruiting wires.
Single wires:
Because many cold climate wine grapes exhibit semi-upright growth, they need help being guided upwards. Single wires require growers to manually attach shoots that did not make contact with their tendrils. This can be done with a tool known as a tapener, a handheld tying tool, which can be time consuming, but is an option for single wires.
Catch wires:
Alternatively, trellises can have double wires, or catch wires that act as a basket to contain shoots as they grow upright. This training is usually much less time consuming and can be modified by making wires moveable in a way that they can be moved to hoop shoots into the middle of the catchwire basket, sections at a time. Growers can also go out when shoots are just barely reaching the first pair of catch wires, and walk along a row while tucking in groups of shoots with your arm.
If you’re using catch wires, don’t wait too long to tuck your shoots! It can become increasingly difficult to tuck in shoots that have grown far beyond the first set of wires, especially if it becomes more stiff through development.
Insect pest highlight: Grape phylloxera
Image: A grape leaf showing early signs of Grape phylloxera (Dactylosphaera vitifoliae) galls, circled in yellow. Photo taken at the UMN Horticultural Research Center, near Chaska, Minnesota (Zone 5a; photo taken by John Thull- UMN HRC Vineyard Manager).
Grape phylloxera (Dactylosphaera vitifoliae) is an insect pest that was historically known for devastating the wine industry after Vitis vinifera grapes were first brought to the U.S. It can cause damage to both the roots and foliage of grapes, but the cold climate grapes grown in Minnesota, which contain genetics from wild American grapes like Vitis riparia, are resistant to root damage and are only susceptible to foliar damage.
Grape phylloxera has multiple generations per growing season. The first generation, known as crawlers, are mobile and emerge in the spring from mother eggs on the trunk and cordons and migrate to the newest grape foliage, which can lead to 40-50 galls per leaf. Thus, the University of Minnesota recommends managing the crawlers as the most critical management stage, especially when growing more vulnerable cultivars like Frontenac.
For vineyards with an extensive history dealing with grape phylloxera, consider timing insecticide applications as soon as early galls are detected.
For more information on management, refer to the Midwest Fruit Pest Management Guide starting on page 161.
Resources:
Tips for managing grape phylloxera (University of Minnesota)
Raspberries
Leafhoppers in high tunnel raspberry production
Images: An unidentified species of light-colored leafhoppers found in a high tunnel stand of raspberries with resulting damage shown in the above photos.Spotted wing drosophila (SWD) is the most dramatically impactful insect pest to affect raspberries, but there are a number of other insect pests that occasionally also show up. These include Japanese beetles, sap beetles, leaf rollers, spider mites, and leafhoppers, shown in the photos above on raspberry plants that were growing in a high tunnel in southern Minnesota.
Leafhoppers are an indirect raspberry pest, meaning that they do not directly harm raspberry fruits like SWD and sap beetles. Instead, leafhoppers are a sucking and piercing pest that reduce the ability for leaves to photosynthesize and produce energy for the developing berries, like thrips and mites, which also feed by piercing and sucking.
Leafhoppers are a unique insect in that their populations cannot overwinter in the Upper Midwest, and come into the region each year traveling on wind currents. In addition to the damage they cause, leafhoppers can also transmit diseases like rubus stunt disease. General management information for leafhoppers is provided in the Midwest Fruit Pest Management Guide.
Resources:
- Raspberry insect pest (University of Minnesota Extension)
- Leafhopper identification (University of California IPM)
Video: Reinforcing raspberry trellis end posts on a small scale production stand.
Image: Click the above image to link to a new short video demonstrating reinforcement of raspberry trellis end posts using supplies on site at a local farm.
Raspberry trellises carry less weight than trellis for some fruit crops like grapes, but overtime end posts can still cave in without good reinforcement. There are a number of trellising options for raspberries, most commonly including V-angled end posts and crossbar trellis posts to extend the containment wire. Similar to trellises for other fruit crops, a well-designed raspberry trellis requires the end posts to be pulled back to maintain a counter force to the other trellis end post(s). The most common way this is done is by anchoring the endpost into the ground using either wire or cable that goes between the end post(s) and an anchor. Some raspberry trellises use in-line posts that go between the two end posts, but many do not, which can put more weight on end-posts.
Follow this video to see one way to reinforce end posts and the guiding wire. Supplies used include spiral anchors, wire rope clips, hook-and-eye turnbuckles, and cable, which were supplies that were available on site that day. The wire rope clips were used to secure the endpost cable, as well as the containment cables that hold the raspberry canes. The hook-and-eye turnbuckles used were fully extended before installing, allowing for future tensioning as time goes on. Anchors are screwed into the ground and provide anchorage for the anchoring cable attached to the endpost.
The above video was filmed and produced by Madeline Wimmer in partnership with Renewing the Countryside’s Farm Buds trip to D& S Gardens, a farm that grows fall-bearing, or primocane-bearing raspberries, among other specialty crops.
Video: Reinforcing raspberry trellis end posts on a small scale production stand.
Resources for more information:
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.
This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.
Resources for more information:
- Planting and trellising raspberries for home and community gardens. (UMN publication, has relevant information for farm settings)
- Anatomy of a grapevine trellis (UMN publication; helpful for understanding function of trellis parts)
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.
This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.
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