Madeline Wimmer- UMN Fruit Production Extension Educator
This fruit update contains information about…
Apples have been going for a ride this year. Minnesota experienced a milder winter in 2023/2024, in which many apples finished their chilling requirements ahead of schedule. In spite of this, most apple cultivars ended up blooming slightly early, but not so early as to put them at risk of frost during bloom. The frequent, heavy rains that affected many parts of Minnesota during spring and early summer created a more challenging situation for managing diseases like apple scab; and this was very evident for urban landscapes where there is noticeable defoliation and foliar symptoms from repeated apple scab infections on susceptible flowering crab apples and fresh eating apple trees.
As the season continues into harvest, many days have been warm and sunny, followed by cooler night temperatures dipping into the mid 50s (°F) in southern Minnesota. These conditions can lead to good color development in apples as warm day temperatures encourage anthocyanin development and cool nights prevent its breakdown, which is similar to how good fall leaf color development occurs as well.
What does this mean for growers? The rate at which an apple's skin color develops in this way is not directly relating with the rate at which the inner flesh is ripening. This means that it might be easy to underestimate apple ripeness, and using a starch test is still going to be one of the best ways to know when apples are at the desired ripeness for harvest. Starch-iodine testing in our last article, “Fruit update: Determining fruit ripeness - August 22, 2024” where you can learn more about this process.
In addition to the heightened color development, growers who had a bumper crop—but did not thin fruits and did not apply stop-drop sprays like ReTain or Fruitone—might be seeing more pre-harvest fruit drop this year. Pre-harvest fruit drop is somewhat a natural process and is more likely to occur on apple varieties with larger fruits and shorter stems, when more than one fruit develops per cluster region. This is because apples will push on one another as they develop and mature in a cluster, and that pressure is sometimes enough to push one off.
The UMN Horticulture Research Center has additionally observed more russeting on apples at their research orchard blocks. For growers who are experiencing a high degree of russeting, keep in mind that apples with conditional russet may not store as well as apples with russet due to the microcracking and altered cuticle that makes their skin more permeable. With more permeable skin, moisture loss happens at a higher rate, and apples in storage are more susceptible to fungal pathogens.
Thank you to Jack Tillman, our UMN Cider Apple Breeder, for his knowledge contribution related to fruit russeting for this section.
MALB look similar to other species of lady beetles, but can be identified by a black “M” shaped pattern behind their head. Yellow sticky card traps can be used for monitoring MALB in the vineyard. When monitoring for MALB, place traps on the outside of a grapevine canopy near the vineyard border, especially on sides closer to neighboring fields.
Vineyards can’t always choose which neighboring crops are close by, but maintaining healthy, uncompromised fruit can help to a point. During years with heavy rains close to harvest, however, berry splitting may be out of the sphere of one’s control as well. For more severe situations, some insecticide options do exist to manage MALB, and for vineyards that hand harvest fruits, harvesters can practice shaking clusters or lightly brushing off beetles. Keep harvest containers closed to keep fruit MALB free until grapes have been processed. If needed, chemical management recommendations for managing MALB can be found starting on page 172 of the Midwest Fruit Pest Management Guide.
Bear in mind the following:
The University of Minnesota has previously shared instructions used by grape breeder Tom Plocher to make a yellowjacket bait that can be used for trap and kill methods:
Additional reading:
Identifying bees and wasps (University of Minnesota)
Social wasps in vineyard (University of Wisconsin-Madison)
Keeping wasps away from wine grapes (University of Minnesota)
Sour rot susceptibility varies among cultivars as well as vineyard locations and relates to how susceptible berries are, or how conducive an environment is to berry injury, cracking, and splitting. A cultivar’s cluster compactness, berry skin thickness, berry softness (2), and how early it ripens also impact sour rot susceptibility and development.
How is sour rot different from botrytis bunch rot?
Late stage botrytis bunch rot leads to sporulation (i.e., fuzz), which visually distinguishes it from sour rot; however, early stage botrytis without sporulation can sometimes look similar to sour rot. Either way, sour rot berries can be distinguished by their vinegar scent and how the berry skins remain somewhat “smooth” as time goes on. Additionally, the sour rot infected fruit will continue to attract more fruit flies due to the vinegar, yeast, and sugar combination that is present and potentially oozing at the infection site (2).
Management
Growers who have concerns about sour rot in their vineyard should monitor for and manage fruit fly populations as a means for prevention. Instructions for creating a trap that will attract both SWD and common fruit flies can be found in the July 17th Fruit Update under the blueberries section. Traps can be installed before or after veraison depending on historical SWD populations. Chemical management strategies usually involve using an insecticide and an antimicrobial product such as OxiDate. When using insecticides be aware of the pre-harvest interval (PHI) associated with products and follow the label of any product used.
Grape section resources cited:
The allegheny blackberry (Rubus allegheniensis) is the most common native blackberry found in parts of Minnesota. Despite this, Minnesota is generally unsuitable for most trailing blackberry cultivars that require warmer growing conditions. Most cultivars that do well are those that produce fruit on primocanes: shoots that emerge and produce fruit during the same growing season. In contrast, floricane blackberries are challenged by harsh winters, but may occasionally do well after milder winter conditions.
This fruit update contains information about…
- Apples
- Seasonal fruit ripening updates: Fruit color development, pre-harvest drop, and russeting.
- Grapes
- Problems with late season insects: Multicolored Asian lady beetle (MALB), social wasps, and fruit flies + a note about sour rot.
- Blackberries
- Cultivars suitable for the Upper Midwest.
- Management practices and harvest updates.
- June-bearing strawberries
- Floral buds are setting now for next year’s crop.
- 2024 Fruit and Veg Updates survey: We want to hear from you!
Apples
Images: Various early-season apple varieties are beginning to show up at the farmer's market in Rochester, MN (Zone 5a). This year, growers have reported noticeable increases in color development, which could related to the occurrence of cooler night temperatures followed by warm, sunny days in SE MN.
Seasonal ripening updates: fruit color development, pre-harvest drop, and russeting
Apples have been going for a ride this year. Minnesota experienced a milder winter in 2023/2024, in which many apples finished their chilling requirements ahead of schedule. In spite of this, most apple cultivars ended up blooming slightly early, but not so early as to put them at risk of frost during bloom. The frequent, heavy rains that affected many parts of Minnesota during spring and early summer created a more challenging situation for managing diseases like apple scab; and this was very evident for urban landscapes where there is noticeable defoliation and foliar symptoms from repeated apple scab infections on susceptible flowering crab apples and fresh eating apple trees.
As the season continues into harvest, many days have been warm and sunny, followed by cooler night temperatures dipping into the mid 50s (°F) in southern Minnesota. These conditions can lead to good color development in apples as warm day temperatures encourage anthocyanin development and cool nights prevent its breakdown, which is similar to how good fall leaf color development occurs as well.
What does this mean for growers? The rate at which an apple's skin color develops in this way is not directly relating with the rate at which the inner flesh is ripening. This means that it might be easy to underestimate apple ripeness, and using a starch test is still going to be one of the best ways to know when apples are at the desired ripeness for harvest. Starch-iodine testing in our last article, “Fruit update: Determining fruit ripeness - August 22, 2024” where you can learn more about this process.
In addition to the heightened color development, growers who had a bumper crop—but did not thin fruits and did not apply stop-drop sprays like ReTain or Fruitone—might be seeing more pre-harvest fruit drop this year. Pre-harvest fruit drop is somewhat a natural process and is more likely to occur on apple varieties with larger fruits and shorter stems, when more than one fruit develops per cluster region. This is because apples will push on one another as they develop and mature in a cluster, and that pressure is sometimes enough to push one off.
The UMN Horticulture Research Center has additionally observed more russeting on apples at their research orchard blocks. For growers who are experiencing a high degree of russeting, keep in mind that apples with conditional russet may not store as well as apples with russet due to the microcracking and altered cuticle that makes their skin more permeable. With more permeable skin, moisture loss happens at a higher rate, and apples in storage are more susceptible to fungal pathogens.
Thank you to Jack Tillman, our UMN Cider Apple Breeder, for his knowledge contribution related to fruit russeting for this section.
Grapes
Images: The multicolored asian lady beetle (left; Harmonia axyridis), social wasps like yellow jackets (middle; Vespula and Dolichovespula spp.), and common fruit flies (Drosophila menogaster) are all insects that can lead to issues with grapes as harvest approaches.
Problems with late season insects
Compared to apples, grapes in the Upper Midwest tend to generally have fewer insect pests that indirectly and directly affect grape clusters. This year, one of the most major insect pests to impact grapes, Japanese beetles, had observably lower populations than previous years, likely due to drought conditions present during larval development last year. This is positive, however, there are still a few other insects that can become problematic in vineyards as harvest approaches and clusters ripen. These include multicolored Asian lady beetles, social wasps, and fruit flies.Multicolored Asian lady beetles
Multicolored Asian lady beetles (MALB; Harmonia axyridis) are more or less likely to be an insect pest depending on a vineyard’s location in relation to where MALB adults are already feeding. Both the juvenile phase and adults act as beneficial insects in soybean fields as they prey on aphids. However, once soybean fields have begun to dry up in preparation for harvest, MALB can move over to nearby vineyards. After they arrive, MALB act as opportunists as they feed on already-damaged berries. Even with only a few numbers, their presence can be loud if get through the crushing process and cause wine taint.MALB look similar to other species of lady beetles, but can be identified by a black “M” shaped pattern behind their head. Yellow sticky card traps can be used for monitoring MALB in the vineyard. When monitoring for MALB, place traps on the outside of a grapevine canopy near the vineyard border, especially on sides closer to neighboring fields.
Vineyards can’t always choose which neighboring crops are close by, but maintaining healthy, uncompromised fruit can help to a point. During years with heavy rains close to harvest, however, berry splitting may be out of the sphere of one’s control as well. For more severe situations, some insecticide options do exist to manage MALB, and for vineyards that hand harvest fruits, harvesters can practice shaking clusters or lightly brushing off beetles. Keep harvest containers closed to keep fruit MALB free until grapes have been processed. If needed, chemical management recommendations for managing MALB can be found starting on page 172 of the Midwest Fruit Pest Management Guide.
Social wasps
Paper wasps (Polistes spp.), and yellowjackets (Vespula and Dolichovespula spp.) are all social wasps in the family Vespidae that can be found in vineyards in the Upper Midwest, with Vespula yellowjackets primarily increasing in number around harvest (1). While most social wasps are predominantly carnivores that feed on caterpillars and other insects, they can still seek out sugars. Berries with pre existing injuries are more susceptible to wasp feeding, however, wasps do have the ability to damage intact berries as well. Because wasps present a stinging issue for those who pick grapes by hand, plan to pick grapes in the morning when wasps are less active. Wear protective clothing as needed, and avoid wearing brightly colored clothing that can attract wasps.Bear in mind the following:
- When thinking about managing wasps, growers should only consider killing wasps if it’s necessary due to the benefits wasps contribute as predatory insects.
- Insecticides are not encouraged for wasp management in vineyards and there are currently no insecticide product labels that list any of the social wasp groups listed above.
- Maintaining healthy fruit is a cultural practice that prevents social wasps from becoming an issue and growers should avoid leaving dropped fruit on the vineyard floor post veraison.
- If necessary, other management options include destroying wasps nests and using a trap and kill approach for managing yellowjackets around harvest.
- Identifying which wasps are problematic for a vineyard is the first step in knowing which type of nest would effectively manage specific populations. Even yellowjackets can vary in how they nest (e.g., ground-nesters and aerial-nesters).
- Trap and kill options can be effective when the appropriate bait is used at the right time (see below).
A trap placed in Tom Plocher’s vineyard located in Washington County, Minnesota (Zone 5a). Photo taken by Tom Plocher and originally posted by Annie Klodd in the UMN Fruit and Veg News article, “Keeping wasps away from wine grapes.”
The University of Minnesota has previously shared instructions used by grape breeder Tom Plocher to make a yellowjacket bait that can be used for trap and kill methods:
- 2 parts water
- 2 parts apple juice
- 2 parts apple cider vinegar
- ½ part sugar
- A few drops of dish soap added after mixing the bait
Additional reading:
Identifying bees and wasps (University of Minnesota)
Social wasps in vineyard (University of Wisconsin-Madison)
Keeping wasps away from wine grapes (University of Minnesota)
Fruit flies and sour rot
Both the common fruit fly (Drosophila menogaster) and spotted wing Drosophila (SWD; D. suzukii) can cause issues in vineyards around harvest time. The common fruit fly is problematic for compromised grape berries when they feed on and lay eggs within wounded fruit and are vectors for acetic acid producing bacteria (Acetobacter spp. and Gluconobacter spp.). SWD in particular prefers to lay eggs in fruits softer than grapes (e.g., blueberries, raspberries, strawberries), however, when they do attempt to pierce through uninjured berries, this too can also lead to sour rot. These bacteria in combination with yeast populations lead to a disease condition known as sour rot. Infected grapes become discolored, break down, and can shrivel up over time, all of which makes them unsuitable for wine production.Sour rot susceptibility varies among cultivars as well as vineyard locations and relates to how susceptible berries are, or how conducive an environment is to berry injury, cracking, and splitting. A cultivar’s cluster compactness, berry skin thickness, berry softness (2), and how early it ripens also impact sour rot susceptibility and development.
How is sour rot different from botrytis bunch rot?
Late stage botrytis bunch rot leads to sporulation (i.e., fuzz), which visually distinguishes it from sour rot; however, early stage botrytis without sporulation can sometimes look similar to sour rot. Either way, sour rot berries can be distinguished by their vinegar scent and how the berry skins remain somewhat “smooth” as time goes on. Additionally, the sour rot infected fruit will continue to attract more fruit flies due to the vinegar, yeast, and sugar combination that is present and potentially oozing at the infection site (2).
Management
Growers who have concerns about sour rot in their vineyard should monitor for and manage fruit fly populations as a means for prevention. Instructions for creating a trap that will attract both SWD and common fruit flies can be found in the July 17th Fruit Update under the blueberries section. Traps can be installed before or after veraison depending on historical SWD populations. Chemical management strategies usually involve using an insecticide and an antimicrobial product such as OxiDate. When using insecticides be aware of the pre-harvest interval (PHI) associated with products and follow the label of any product used.
Grape section resources cited:
- Guédot, C.; Hietala-Henschell, K.; Lois, A.N. Species Composition, Abundance and Seasonal Phenology of Social Wasps (Hymenoptera: Vespidae) in Wisconsin Vineyards. Insects 2018, 9, 57. https://doi.org/10.3390/insects9020057
- Hall, M. and Klodd, A. Managing sour rot and other grape bunch rots. YouTube webinar available on UMN Extension Small Farms: https://www.youtube.com/watch?v=HG_gZjTj9_E
Blackberries
Images; Blackberries in a number of different growth phases: 1) bloom, 2) fruit set and ripening 3) on the shrub ready for harvest, 4) blackberries at postharvest. Blackberries in these photos were grown at Firefly Berries located in Olmsted County (Zone 5a). Firefly Berries grow several different blackberry varieties, two of which were passed along from previous growers.
The allegheny blackberry (Rubus allegheniensis) is the most common native blackberry found in parts of Minnesota. Despite this, Minnesota is generally unsuitable for most trailing blackberry cultivars that require warmer growing conditions. Most cultivars that do well are those that produce fruit on primocanes: shoots that emerge and produce fruit during the same growing season. In contrast, floricane blackberries are challenged by harsh winters, but may occasionally do well after milder winter conditions.
Firefly Berries is a diverse fruit farm located in Olmsted County (Zone 5a) that grows several types of blackberry varieties. Two varieties were passed along from previous owners, and one variety, Prime-Ark 45, was more recently established. Prime-Ark 45 is a primocane producing variety that can additionally bear on floricanes the following season- a practice known as double bearing. Prime-Ark 45 is suitable for warmer Minnesotan regions as it is listed to survive in USDA hardiness zones 5a and warmer.
Distinguishing a blackberry from blackcap raspberries
Blackberries and blackcap raspberries are often confused with one another, but one good way to tell them apart is to look at the point where the berry detached from the plant: does it contain an off-white receptacle or is vacant? The receptacle is the fleshy core upon which the aggregate fruits develop. For blackberries, the receptacle remains intact with the berries and detaches from the plant, while in raspberries the receptacle remains on the plant (see image below).
Harvest is long over for June-bearing strawberries, and for growers who practice postharvest strawberry bed renovation, that time has also passed. Despite this, June-bearing strawberries still require attention to watering and care at this time of year. Why? Because June-bearing strawberries are short day plants, which means that as we transition to shorter days during this time of year, the plants begin to set floral buds for the 2025 growing season.
It’s recommended to irrigate strawberry beds about one inch of water per week and adjust for additional rainfall that occurs. Strawberry growers in warmer climates may choose to additionally fertilize at this time, however, it's recommended to applying nitrogen immediately after harvest ends rather than later in the season in Minnesota and other cold climate regions.
Additional reading:
June-bearing strawberry nutrient management (University of Minnesota)
Distinguishing a blackberry from blackcap raspberries
Blackberries and blackcap raspberries are often confused with one another, but one good way to tell them apart is to look at the point where the berry detached from the plant: does it contain an off-white receptacle or is vacant? The receptacle is the fleshy core upon which the aggregate fruits develop. For blackberries, the receptacle remains intact with the berries and detaches from the plant, while in raspberries the receptacle remains on the plant (see image below).
Images: Blackberries (left) and blackcap raspberries appear similar, but are distinguished primarily by whether or not the receptacle remains within the berry.
June-bearing strawberries
Floral buds are setting now for next year’s cropHarvest is long over for June-bearing strawberries, and for growers who practice postharvest strawberry bed renovation, that time has also passed. Despite this, June-bearing strawberries still require attention to watering and care at this time of year. Why? Because June-bearing strawberries are short day plants, which means that as we transition to shorter days during this time of year, the plants begin to set floral buds for the 2025 growing season.
It’s recommended to irrigate strawberry beds about one inch of water per week and adjust for additional rainfall that occurs. Strawberry growers in warmer climates may choose to additionally fertilize at this time, however, it's recommended to applying nitrogen immediately after harvest ends rather than later in the season in Minnesota and other cold climate regions.
Additional reading:
June-bearing strawberry nutrient management (University of Minnesota)
2024 Fruit and Veg Updates survey: We want to hear from you!
The end of the 2024 growing season is approaching and we want to hear from you about what was useful and enjoyable to read, as well as what you would like to read more about next growing season. And, if some information wasn't as helpful we want to hear that too!❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖❖
The University of Minnesota Extension fruit production program would like to extend a thank-you to our fruit grower partners who make these reports possible.
Non-credited photos in these publications were taken by the author, Madeline Kay Wimmer, M.S.
The University of Minnesota Extension fruit production program would like to extend a thank-you to our fruit grower partners who make these reports possible.
Non-credited photos in these publications were taken by the author, Madeline Kay Wimmer, M.S.
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