Madeline Wimmer- UMN Fruit Production Extension Educator
This fruit update contains information about…
Second generation codling moth
The second generation of codling moth adults are typically expected to emerge around 1,060 degree day units (DD) after the first biofix date, which was recorded when the first generation codling moth adults were initially trapped.
The University of Minnesota Horticulture Research Center (UMN HRC) is forecasted to reach 1,047 DD on July 20th, with the accumulation at baseline 50F and originally starting from May 25th (i.e., the biofix date for the first codling moth generation). This means the UMN HRC can anticipate finding second generation adult codling moths within the next week or so as long as populations are active. Growers looking to begin monitoring for second generation codling moths should plan to check traps around 2 times per week until moths have been found within the traps for three consecutive checks where the final day becomes the recorded biofix date. Similar to first generation codling moths, eggs usually hatch around 160 DD after the recorded biofix date. Most growers can plan to apply insecticides at 200-250 DD unless the codling moth pressure is observed to be very high, for which scenario some growers may choose to spray earlier (i.e., between 160-250 DD, as recommended by University of California IPM).
Additional resources:
Are you seeing downy or powdery mildew on grape clusters?
It’s easy to imagine that a cluster infected with powdery mildew would look powdery in appearance; however, downy mildew cluster infections can also look somewhat powdery, so how can growers distinguish the two from each other? The above photos exemplify both downy mildew (Plasmopara viticola) (1) and powdery mildew (Uncinula necator) (2) infections on grape clusters. At a glance, they look very similar, but the powdery mildew on fruit clusters has an appearance similar to an actual powder whereas downy mildew may look more like granulated sugar or wet powdered sugar. On a leaf surface, downy symptoms are yellow to light green spots or “oil spots” (upperside) and white powder (underside), while powdery symptoms tend to be white/grayish powdery coating (upperside).
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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.
This fruit update contains information about…
- Apples- second generation codling moth.
- Grapes- disease updates and russeting and cracking.
- Blueberries- harvest season and insect pest updates.
- Additional fruit updates- black currants, aronia berries, and kiwiberries.
Apples
Images: Apples showing fruit color development as they continue to ripen at Keepsake Cidery near Northfield, MN (left image; Zone 5a). Cutting open an apple with a visible entry point can reveal evidence of larval damage within a developing apple showing leftover frass and damage to the ovaries and developing seeds (right image).
Second generation codling moth
The second generation of codling moth adults are typically expected to emerge around 1,060 degree day units (DD) after the first biofix date, which was recorded when the first generation codling moth adults were initially trapped.
The University of Minnesota Horticulture Research Center (UMN HRC) is forecasted to reach 1,047 DD on July 20th, with the accumulation at baseline 50F and originally starting from May 25th (i.e., the biofix date for the first codling moth generation). This means the UMN HRC can anticipate finding second generation adult codling moths within the next week or so as long as populations are active. Growers looking to begin monitoring for second generation codling moths should plan to check traps around 2 times per week until moths have been found within the traps for three consecutive checks where the final day becomes the recorded biofix date. Similar to first generation codling moths, eggs usually hatch around 160 DD after the recorded biofix date. Most growers can plan to apply insecticides at 200-250 DD unless the codling moth pressure is observed to be very high, for which scenario some growers may choose to spray earlier (i.e., between 160-250 DD, as recommended by University of California IPM).
Additional resources:
- University of California IPM: Codling moth
- University of California IPM: Codling moth degree day reference table
- Cornell virtual scouting meeting 2 (2024, YouTube video)
Grapes
Images: 1) Downy mildew (Plasmopara viticola) shows up on grape clusters as a granulated-sugar or wet powdered sugar appearance on the berry surfaces. 2) Grape clusters showing a powdery film indicative of powdery mildew (Uncinula necator) cluster infection. Additionally, the grapevine in the first photo has been impacted by herbicides. Photo (1) submitted to UMN Extension from a grower in Morrison County (Zone 4a).
Are you seeing downy or powdery mildew on grape clusters?
It’s easy to imagine that a cluster infected with powdery mildew would look powdery in appearance; however, downy mildew cluster infections can also look somewhat powdery, so how can growers distinguish the two from each other? The above photos exemplify both downy mildew (Plasmopara viticola) (1) and powdery mildew (Uncinula necator) (2) infections on grape clusters. At a glance, they look very similar, but the powdery mildew on fruit clusters has an appearance similar to an actual powder whereas downy mildew may look more like granulated sugar or wet powdered sugar. On a leaf surface, downy symptoms are yellow to light green spots or “oil spots” (upperside) and white powder (underside), while powdery symptoms tend to be white/grayish powdery coating (upperside).
In regards to management, both diseases are best managed with a preventative approach using appropriate fungicides timed throughout the growing season. In regards to downy mildew, one positive note is that clusters tend to become more resistant to the disease as they develop. During circumstances where cluster infections occur, removing infected clusters from the vine(s), out of the vineyard, and destroying them is a good way to reduce inoculum and mitigate issues down the road. Leaving mummified fruits on the vineyard floor can help encourage decomposition of overwintering spores, but will carry any inoculum that does not break down, leading to increased disease pressure. Refer to the Midwest Fruit Pest Management Guide for information related to chemical management for both downy and powdery mildew.
Additional reading:
Image: Russeting on grape berries shows up as a rough, scab-like texture and is more likely to happen when microcracks form during high-humidity conditions, and with fast changes in vine water uptake.
Russeting in a physiological response to micro-cracks forming on the outer epidermal fruit layer, known as the cuticle. The russeting itself is composed of a number of cells for the purpose of sealing microcrack wounds to protect the fruit. Some apple fruit cultivars are reputedly known for and even appreciated for their russeting, but it is not usually desirable in grapes. Russeting on grapes often occurs with high-humidity conditions, with fast changes in grapevine water uptake, and high winds can be an additional factor leading to microcrack formation. Grapes with a high degree of russeting on the skin may impact wine quality by disrupting the contribution from compounds located in the grape skins, especially for red wine grapes, which are traditionally fermented with their skins on. However, for the most part, minor russeting on grapes is not a major concern in regards to fruit quality and most growers can expect to tolerate the condition.
Thank you to Soon Li Teh, UMN Grape Breeder and Extension Specialist for his contributions to authorship in the grape section of this week’s fruit update. Thank you also to Drew Horton, UMN Enology Specialist for contributing knowledge about how russeting can impact wine quality.
Spotted wing drosophila
Blueberry harvest season has begun in the southern parts of Minnesota, and one key pest for blueberry and other berry growers is spotted wing drosophila (SWD; Drosophila suzukii). Spotted wing drosophila causes damage to fruits through egg laying, and is distinctive from other fruit flies in its ability to lay eggs in under ripened fruits. This is possible because of SWD adult serrated ovipositors that can cut into thicker skins and breathing tubes that connect to the eggs, which increase their chance for survival. Monitoring for SWD involves using traps, which includes commercial traps and homemade options.
Additional reading:
- For more information on powdery mildew, refer to the July 3rd, 2024 fruit update.
- For more information on downy mildew, refer to the June 18th, 2024 fruit update.
Russeting in a physiological response to micro-cracks forming on the outer epidermal fruit layer, known as the cuticle. The russeting itself is composed of a number of cells for the purpose of sealing microcrack wounds to protect the fruit. Some apple fruit cultivars are reputedly known for and even appreciated for their russeting, but it is not usually desirable in grapes. Russeting on grapes often occurs with high-humidity conditions, with fast changes in grapevine water uptake, and high winds can be an additional factor leading to microcrack formation. Grapes with a high degree of russeting on the skin may impact wine quality by disrupting the contribution from compounds located in the grape skins, especially for red wine grapes, which are traditionally fermented with their skins on. However, for the most part, minor russeting on grapes is not a major concern in regards to fruit quality and most growers can expect to tolerate the condition.
Thank you to Soon Li Teh, UMN Grape Breeder and Extension Specialist for his contributions to authorship in the grape section of this week’s fruit update. Thank you also to Drew Horton, UMN Enology Specialist for contributing knowledge about how russeting can impact wine quality.
Blueberries
Images: Fully ripened blueberries (left) ready for harvest and a spotted wing drosophila (SWD; Drosophila suzukii) trap used to monitor and catch SWD populations that can cause damage through egg laying in under ripe fruits. Photos taken at Blue Fruit Farm located near Winona, MN (Zone 5a).
Blueberry harvest season has begun in the southern parts of Minnesota, and one key pest for blueberry and other berry growers is spotted wing drosophila (SWD; Drosophila suzukii). Spotted wing drosophila causes damage to fruits through egg laying, and is distinctive from other fruit flies in its ability to lay eggs in under ripened fruits. This is possible because of SWD adult serrated ovipositors that can cut into thicker skins and breathing tubes that connect to the eggs, which increase their chance for survival. Monitoring for SWD involves using traps, which includes commercial traps and homemade options.
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:
Growers are additionally encouraged to check fruits for larval presence twice a week as a measure of detection- this can be done by visual inspection or using the salt flotation method. SWD can become challenging quickly because SWD eggs can hatch within 1-3 of laying and larvae finish feeding within days before they begin to pupate for 4-15 days.
- 1 Tbsp Active dry yeast
- 4 Tbsp Table sugar
- 12 oz Water
- 2 drops of Dish soap
Growers are additionally encouraged to check fruits for larval presence twice a week as a measure of detection- this can be done by visual inspection or using the salt flotation method. SWD can become challenging quickly because SWD eggs can hatch within 1-3 of laying and larvae finish feeding within days before they begin to pupate for 4-15 days.
Many chemical management options exist and are listed on the Midwest Fruit Pest Management Guide. One organic product, OxiDate, is also available for SWD management. Additionally, organic and conventional growers who are dealing with SWD should practice frequent picking, removing and destroying infected, “soft fruits" from the area, and plan to cool fruits down quickly after harvest to slow down any SWD development within fruit. New growers may also choose fruit cultivars that ripen earlier in an attempt to escape the time period in which SWD is active.
Additional resources:
University of Wisconsin: Biology of the spotted wing drosophila
Additional fruit updates
Images: 1) Black currants reaching full ripeness and ready for harvest, and 2) aronia berries beginning to change colors indicating progression of their ripening at Blue Fruit Farm located near Winona, MN (Zone 5a). 3) Kiwiberries are showing healthy signs of fruit development at the UMN Horticulture Research Center, near Chaska, MN (Zone 5a).
Black currants
In Southeastern Minnesota, black currants (Ribes nigrum) are beginning to fully ripen. Black currants are a fruit crop with a unique taste and a strong following from consumers who admire it. They have been a cultural staple in Eastern Europe, where the leaves are additionally used for tea. The University of Minnesota breeding program has released two cultivated black currant varieties: Ben Chaska and Ben Como, both of which are described on our MN Hardy website. Black currants can be consumed fresh, or used to make jam, juice, or incorporated into fermented beverage products.
Additional reading:
University of Wisconsin: Is aronia susceptible to spotted wing drosophila?
While kiwiberries are related to the kiwi fruits (A. deliciosa) that many people are familiar with eating, kiwiberry plants can tolerate much colder mid-winter temperatures, but are still limited to Zone 5 regions or higher.
The University of Minnesota has dedicated research to explore kiwiberry science and breeding for high quality berries and bines. Some of the UMN breeding goals and research has focused on reducing oxalic acid content in fruit, increasing hardiness, and selecting for fruits that have desirable sugar, acid, and flavor profiles.
Additional reading:
Aronia berries
Also known as black chokeberries (Aronia melanocarpa)—but not choke cherries (Prunus virginiana)—the aronia plants that are grown commercially are cultivated varieties that taste different from ornamental aronia used in landscaping. This fruit crop has its own flavor profile that can complement other berries in juices and preserves, or it can stand on its own in some dessert recipes and savory sauces. Aronia plants are susceptible to some diseases, and—while the berries have thick skins—when the berries are damaged, they can be vulnerable to SWD damage. Right now, aronia berries are ripening and developing color in southern Minnesota right now, which has been reported as somewhat early according to some growers in the region.Additional reading:
University of Wisconsin: Is aronia susceptible to spotted wing drosophila?
Kiwiberries
Kiwiberries (Actinidia kolomikta, A. arguta, and A. polygama) grow as a woody bine, which is different from a vine in that it does not have tendrils, but instead wraps around climbing structures with its stems. Because of its growth habit, it requires a trellis system for training and is pruned annually. Its dioecious floral biology means that it produces male and female flowers on separate plants where one male kiwiberry plant can act as a pollinizer for 5-8 female kiwiberry plants. Kiwiberries rely on insect pollinators to successfully complete pollination.While kiwiberries are related to the kiwi fruits (A. deliciosa) that many people are familiar with eating, kiwiberry plants can tolerate much colder mid-winter temperatures, but are still limited to Zone 5 regions or higher.
The University of Minnesota has dedicated research to explore kiwiberry science and breeding for high quality berries and bines. Some of the UMN breeding goals and research has focused on reducing oxalic acid content in fruit, increasing hardiness, and selecting for fruits that have desirable sugar, acid, and flavor profiles.
Additional reading:
- UMN Minnesota Fruit Research: Get to know the kiwiberry
- UMN Minnesota Fruit Research: Choosing kiwiberry varieties
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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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