Madeline Wimmer- UMN Fruit Production Extension Educator
Apples:
Images: A step by step demonstration of hand removal of a newly emerging water sprout from a larger scaffold branch on a freestanding central leader trained apple tree. Image from Sekapp Orchard in Olmsted County, MN (Zone 5a).
By the time apple fruitlets begin to grow past 10 mm in circumference, a good amount of shoot growth has typically occurred. In SE Minnesota orchards, many fruits are between 12-24 mm depending on the location, variety, and other factors; vegetative shoots were around 7 inches long and still tender.
Removing newly emerging water sprouts:
This is also the time period when water sprouts emerge on older branches. Water sprouts are shoots that emerge on scaffold branches on the inside of the tree canopy. They are often unnecessary, taking up more energy than they can give because they are shaded, and thus photosynthetically less active.
Water sprouts are commonly removed during dormancy, but this can lead to a pattern known as, “cut and regrowth,” where new shoots grow from the location where the water sprouts were pruned off. This cycle can repeat year after year, and eventually add up in regards to the time and effort needed to manage it.
The other option to manage water sprouts is to remove them as they emerge and are still tender. This can usually be done by hand, and does not require pruning shears, unlike removal during the dormant season, and the resulting wounds tend to be much smaller. The optimal time to remove water sprouts is when shoots are under 8 inches.
Apple scab update
Mature apple scab spores, known as ascospores, are at their highest presence from pink growth stage to the end of bloom; and one to two weeks after the final petal fall most ascospores have finished being released. The Cornell NEWA apple scab prediction model indicates that primary scab season is over based on the UMN Horticulture Research Center’s April 16th green tip date this year.
Primary scab refers to the infections caused by spores from overwintering fruiting bodies (similar to microscopic mushrooms that house spores). If an orchard experiences infections from the primary spores, those infection sites will eventually begin to produce asexual spores known as conidia which can cause further infections. The infections that result from spores are called secondary infection. This is why it is beneficial to more intensely manage apple scab until the primary spores have fully discharged, after which point there will be very little infection pressure if no primary infections occurred.
Growers who are managing secondary scab infections can continue their management program and refer to tools like the Midwest Fruit Pest Management Guide for more information.
Images: The above photos are Marquette (left), Brianna (middle), and Itasca (right) all from the same vineyard near Eyota, Minnesota (Zone 5a) with an average 6–7 leaves separated from the shoots. The Marquette in this vineyard have much shorter internodes than Brianna and Itasca and many vines suffered from either delayed or failed budbreak.
We’re getting closer to bloom for grapes in southern Minnesota! The above photos are from a vineyard in Olmsted County, Minnesota where most shoots are between E-L stages 12–14 showing between 5–7 leaves separated from the growing shoot. A number of vines in this vineyard, mostly Marquette, experienced either failed or delayed budbreak.
The grower in this vineyard is planning to flag dead grapevines this year for their removal during next winter’s dormant pruning. Stay tuned for a future week summarizing our results from the grape grower’s failed budbreak survey we launched earlier this season. There’s still time to take this survey if you would like to report on your grapes: 2025 Grape Growers Bud Break Survey.
Images: There are two times of the growing season when vineyards typically take petiole samples: bloom and early veraison. Both have their own unique requirements for preferred petiole samples shown here as the basal leaf at bloom and the 5-7 leaves from the most recently matured, unfolded leaf near the shoot tip.
About petiole sampling:
There are multiple reasons why foliar and fruit nutrient deficiency symptoms can show up beyond having a soil nutrient deficiency. What nutrients get into a plant from the soil can be impacted by soil pH, competition with other nutrients, as well as plant health.
Petiole nutritional analysis uses a number of leaf stems to gather a general snapshot of the nutrient profile within a plant at a given time, and can be helpful to inform nutrient management programs within a vineyard. Petiole nutrition reports can be read alongside soil nutrition levels to track plant health in general, and more often to diagnose nutritional deficiencies when symptoms appear.
Because plant nutrient (e.g., nitrogen, calcium, zinc) levels change based on a plant’s demands, there is not one baseline nutrient profile for reference throughout the whole growing season. Instead, references exist for specific times of the year for a given plant. For example, reference points for cold climate grapes are for samples taken at either bloom or early veraison- the time period in which the grape berries begin to show colors as the green chlorophyll degrades (stage 35 of the E-L Growth stage Chart).
How to take samples for petiole analysis:
The general process for collecting petiole samples at bloom is to take the petiole across from the basal flower cluster, which is the flower cluster closest to the cordon and fruiting wire. Your sample should contain 75–100 petioles from 25–50 representative grapevines—this could be a specific vineyard region or variety. It also helps to sample vines that are the same age and grown on similar soil.
If you can’t get to sampling during bloom this year, you can plan to take samples during early veraison. The instructions for early-veraison sampling are different from bloom: the last leaf to mature, located closest to the shoot tip is counted as 1, and then samples are taken from the 5th to 7th leaf below that leaf.
For more information about foliar and petiole nutritional analysis, check out this week’s article:
Test don’t guess: Is foliar nutritional analysis right for your fruit crops this growing season?
Resources:
Tissue and soil nutrient testing for cold climate grapes (UMN webpage)
Taking a foliar sample: Vineyards and orchards (UMN instructional YouTube video)
Images: A spotted wing drosophila (SWD; Drosophila suzukii) trap is often made from a liquid solution and is used to monitor SWD populations . Photo taken at Blue Fruit Farm located near Winona, MN (Zone 5a).
Other factors make SWD management more complicated, including how SWD eggs hatch and larvae begin to pupate within the fruit, but the pupae can either stay within the fruit, or drop out and fall to the ground. SWD populations additionally go through many short life cycles after appearing at a given growing site. They tend to favor humid, shady environments and warm temperatures. Some recent research with the University of Minnesota has shown that wooded edges with wild honeysuckle can harbor early populations of SWD before they enter a managed site. This can also happen with other wild fruit species.
Read more about UMN research on wild honeysuckle species and spotted wing drosophila management here:
Invasive honeysuckles: A dual threat to Minnesota’s environment and berry growers
Lured traps can be used to monitor SWD adults. Because homemade options and some lures replicate scents similar to rotting fruit (e.g., yeast, and sometimes vinegar) adult females attracted to these particular lures may not be laying eggs at the time they are trapped, as most egg-laying females are in search of fruit that is ripening rather than overripe and fermented.
This is why traps like these are used for monitoring, but are likely to be unsuccessful for management purposes. Some attract and kill options have been more recently researched and developed (see information in next section), which have their own mechanisms to attract various adult stages.
Resources from the University of Wisconsin recommend creating homemade traps by using a 32 ounce deli cup with holes drilled into the lid, filled with the following recipe:
Apples:
- Growth stage updates: Apples between 12–24 mm, rapid shoot growth
- Removing newly emerging water sprouts
- Apple scab update
- Growth stage update: 6–8 leaves separated
- Bloom: Petiole sampling for nutrient analysis
- Pest highlight: Spotted Wing Drosophila (SWD)
- About SWD
- Monitoring SWD adults and larvae
- Managing SWD
Apples
Growth stage updates: Fruitlets between 12–24 mm, rapid shoot growth
Images: A step by step demonstration of hand removal of a newly emerging water sprout from a larger scaffold branch on a freestanding central leader trained apple tree. Image from Sekapp Orchard in Olmsted County, MN (Zone 5a).
By the time apple fruitlets begin to grow past 10 mm in circumference, a good amount of shoot growth has typically occurred. In SE Minnesota orchards, many fruits are between 12-24 mm depending on the location, variety, and other factors; vegetative shoots were around 7 inches long and still tender.
Removing newly emerging water sprouts:
This is also the time period when water sprouts emerge on older branches. Water sprouts are shoots that emerge on scaffold branches on the inside of the tree canopy. They are often unnecessary, taking up more energy than they can give because they are shaded, and thus photosynthetically less active.
Water sprouts are commonly removed during dormancy, but this can lead to a pattern known as, “cut and regrowth,” where new shoots grow from the location where the water sprouts were pruned off. This cycle can repeat year after year, and eventually add up in regards to the time and effort needed to manage it.
The other option to manage water sprouts is to remove them as they emerge and are still tender. This can usually be done by hand, and does not require pruning shears, unlike removal during the dormant season, and the resulting wounds tend to be much smaller. The optimal time to remove water sprouts is when shoots are under 8 inches.
However, because many pathogens are active at this time of year, there can still be risk for infection, especially with fire blight (Erwinia amylovora), which can enter through small wounds. It's important to avoid doing this type of shoot removal right before, during, or immediately after a rain event.
Apple scab update
Mature apple scab spores, known as ascospores, are at their highest presence from pink growth stage to the end of bloom; and one to two weeks after the final petal fall most ascospores have finished being released. The Cornell NEWA apple scab prediction model indicates that primary scab season is over based on the UMN Horticulture Research Center’s April 16th green tip date this year.
Primary scab refers to the infections caused by spores from overwintering fruiting bodies (similar to microscopic mushrooms that house spores). If an orchard experiences infections from the primary spores, those infection sites will eventually begin to produce asexual spores known as conidia which can cause further infections. The infections that result from spores are called secondary infection. This is why it is beneficial to more intensely manage apple scab until the primary spores have fully discharged, after which point there will be very little infection pressure if no primary infections occurred.
Growers who are managing secondary scab infections can continue their management program and refer to tools like the Midwest Fruit Pest Management Guide for more information.
Grapes
Growth stage update: 6–8 leaves separated
We’re getting closer to bloom for grapes in southern Minnesota! The above photos are from a vineyard in Olmsted County, Minnesota where most shoots are between E-L stages 12–14 showing between 5–7 leaves separated from the growing shoot. A number of vines in this vineyard, mostly Marquette, experienced either failed or delayed budbreak.
The grower in this vineyard is planning to flag dead grapevines this year for their removal during next winter’s dormant pruning. Stay tuned for a future week summarizing our results from the grape grower’s failed budbreak survey we launched earlier this season. There’s still time to take this survey if you would like to report on your grapes: 2025 Grape Growers Bud Break Survey.
Bloom: Petiole sampling for nutrient analysis
About petiole sampling:
There are multiple reasons why foliar and fruit nutrient deficiency symptoms can show up beyond having a soil nutrient deficiency. What nutrients get into a plant from the soil can be impacted by soil pH, competition with other nutrients, as well as plant health.
Petiole nutritional analysis uses a number of leaf stems to gather a general snapshot of the nutrient profile within a plant at a given time, and can be helpful to inform nutrient management programs within a vineyard. Petiole nutrition reports can be read alongside soil nutrition levels to track plant health in general, and more often to diagnose nutritional deficiencies when symptoms appear.
Because plant nutrient (e.g., nitrogen, calcium, zinc) levels change based on a plant’s demands, there is not one baseline nutrient profile for reference throughout the whole growing season. Instead, references exist for specific times of the year for a given plant. For example, reference points for cold climate grapes are for samples taken at either bloom or early veraison- the time period in which the grape berries begin to show colors as the green chlorophyll degrades (stage 35 of the E-L Growth stage Chart).
How to take samples for petiole analysis:
The general process for collecting petiole samples at bloom is to take the petiole across from the basal flower cluster, which is the flower cluster closest to the cordon and fruiting wire. Your sample should contain 75–100 petioles from 25–50 representative grapevines—this could be a specific vineyard region or variety. It also helps to sample vines that are the same age and grown on similar soil.
If you can’t get to sampling during bloom this year, you can plan to take samples during early veraison. The instructions for early-veraison sampling are different from bloom: the last leaf to mature, located closest to the shoot tip is counted as 1, and then samples are taken from the 5th to 7th leaf below that leaf.
For more information about foliar and petiole nutritional analysis, check out this week’s article:
Test don’t guess: Is foliar nutritional analysis right for your fruit crops this growing season?
Resources:
Tissue and soil nutrient testing for cold climate grapes (UMN webpage)
Taking a foliar sample: Vineyards and orchards (UMN instructional YouTube video)
Berry crops
Pest highlight: Spotted wing drosophila (SWD)
Images: A spotted wing drosophila (SWD; Drosophila suzukii) trap is often made from a liquid solution and is used to monitor SWD populations . Photo taken at Blue Fruit Farm located near Winona, MN (Zone 5a).
About SWD:
Spotted wing drosophila (SWD; Drosophila suzukii) is a major berry pest that is a fruit fly with a biological advantage. Its serrated ovipositor—a saw-like, egg-laying mechanism—allows it to lay eggs in ripening fruits, whereas most fruit flies can only lay eggs in overripened, soft fruits.Other factors make SWD management more complicated, including how SWD eggs hatch and larvae begin to pupate within the fruit, but the pupae can either stay within the fruit, or drop out and fall to the ground. SWD populations additionally go through many short life cycles after appearing at a given growing site. They tend to favor humid, shady environments and warm temperatures. Some recent research with the University of Minnesota has shown that wooded edges with wild honeysuckle can harbor early populations of SWD before they enter a managed site. This can also happen with other wild fruit species.
Read more about UMN research on wild honeysuckle species and spotted wing drosophila management here:
Invasive honeysuckles: A dual threat to Minnesota’s environment and berry growers
Monitoring SWD adults and larvae:
Adults:Lured traps can be used to monitor SWD adults. Because homemade options and some lures replicate scents similar to rotting fruit (e.g., yeast, and sometimes vinegar) adult females attracted to these particular lures may not be laying eggs at the time they are trapped, as most egg-laying females are in search of fruit that is ripening rather than overripe and fermented.
This is why traps like these are used for monitoring, but are likely to be unsuccessful for management purposes. Some attract and kill options have been more recently researched and developed (see information in next section), which have their own mechanisms to attract various adult stages.
Resources from the University of Wisconsin recommend creating homemade traps by using a 32 ounce deli cup with holes drilled into the lid, filled with the following recipe:
- 1 Tbsp Active dry yeast
- 4 Tbsp Table sugar
- 12 oz Water
- 2 drops of Dish soap
Most resources do not list an action threshold for SWD based on trap catches, and various management strategies can be put in place prior or starting when SWD adults are first captured.
Larvae:
Fruits can additionally be checked for larvae as they grow past the point of susceptibility when they soften, accumulate sugar, and begin to show color. Fruits can be checked for larvae twice per week through visual inspection or using the salt flotation method.
Organic and conventional chemical management options used by themselves can be expensive for the effectiveness and longevity due to SWD's fast life cycle and other factors. Organic and conventional growers observing SWD adults or larvae can practice frequent harvesting, removing and destroying infested, “soft fruits" from the area, and plan to cool fruits down quickly after harvest to slow down any SWD development within fruit.
A lot of research has gone into learning about new methods to control SWD in fruit crops in various settings in the past decade. This includes the attract and kill options listed above, along with exclusion netting, floor and water management, and the release and encouragement of natural predators and parasitoids.
Larvae:
Fruits can additionally be checked for larvae as they grow past the point of susceptibility when they soften, accumulate sugar, and begin to show color. Fruits can be checked for larvae twice per week through visual inspection or using the salt flotation method.
Managing SWD:
The University of Minnesota's FruitEdge website has a web landing page with information about SWD biology and management, the SWD trapping network, and the trap network historical data. Resources related to chemical management can be found on the SWD biology and management webpage on the FruitEdge site, along with the Midwest Fruit Pest Management Guide.Organic and conventional chemical management options used by themselves can be expensive for the effectiveness and longevity due to SWD's fast life cycle and other factors. Organic and conventional growers observing SWD adults or larvae can practice frequent harvesting, removing and destroying infested, “soft fruits" from the area, and plan to cool fruits down quickly after harvest to slow down any SWD development within fruit.
A lot of research has gone into learning about new methods to control SWD in fruit crops in various settings in the past decade. This includes the attract and kill options listed above, along with exclusion netting, floor and water management, and the release and encouragement of natural predators and parasitoids.
Webinar recording:
The UMN Extension Fruit Program delivered a winter webinar that went over SWD biology and recent research and innovative management practices, and is available for viewing on our UMN Small Farms YouTube Channel:
Video: Spotted wing drosophila management: Recent insights and innovations
Video: Spotted wing drosophila management: Recent insights and innovations
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.
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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