Madeline Wimmer- UMN Fruit Production Extension Educator
This fruit update contains information about…
Images: Zestar!® (left) and Rave®/First Kiss® (right) shown here in “tight cluster” growth stage, where floral buds are beginning to be exposed, but are still tightly grouped. Photo (left) taken at Northwoods Apple Orchard in Olmsted County, Minnesota (04/15, Zone 5a) and photo (right) at the University of Minnesota Horticultural Research Center (04/29, UMN HRC; Zone 5a, photo taken by Kate Scapanski, UMN Researcher).
The next major apple growth stage after 1/2 inch green is called tight cluster, in which apple floral bud tips are visible, yet tightly compact, as surrounding leaves continue to mature. In fruit production, critical temperatures are temperature thresholds that signify when damage to buds from cold or freezing temperatures begins. For the tight cluster phase, research has shown that 10% of apple buds will likely die when temperatures lower to 27°F, and 90% of buds will likely die at 21°F. Fortunately, most regions in Minnesota where apples are currently at the tight cluster stage are not expecting to reach temperatures near or below the critical threshold. Refer to the Midwest Fruit Pest Management Guide on page 13 to learn more about which insect pests can coincide with tight cluster.
Images: (Right) Managing European red mite (ERM) overwintering eggs is an approach to keeping populations under control. ERM eggs are most effectively managed at the apple ½ inch green growth stage. Left photo credited to University of Georgia Plant Pathology.
Introduction:
Of the three different pest mites that can affect apple orchards, European red mite (ERM, Panonychus ulmi) can be one of the most problematic. ERM are spider mites, about 0.42 mm in length, and reddish-brown in appearance. Their host range primarily covers plants in the Rosaceae, or rose family, which includes apples.
ERM overwinter as eggs on or near tree buds and fruiting spurs before they hatch in the spring. After the first adult generation of the growing season matures, females begin to lay eggs on leaves around the time of petal fall. ERM populations complete several generations throughout the growing season. Their pest habits are unique as their populations and activity often decrease in the middle of the summer due to natural enemy activity and hot, dry conditions. ERM target apple leaves, leading to a stippling injury that reduces photosynthetic activity and leaf bronzing, which can result in smaller fruit sizes.
Note on predatory mites:
Before discussing solutions for managing ERM, it is important to understand that many mite populations, even when present, can be less damaging when populations are balanced in the presence of predatory mites. There are a number of predatory mite species that exist (ex. Neoseiulus fallacis, Amblyseius andersoni, and Typhlodromus pyri). Many predatory mites are about the same size as a spider mite, with a more pear or oblong body shape and lighter color.
This fruit update contains information about…
- Apples
- Growth stage update: tight cluster.
- Pest highlight: European red mites (ERM) + Beneficial insect highlight: Predatory mites
- Grapes
- About grapevine foliar and fruit diseases.
- Additional fruit crop growth stage updates: Tart cherry, Pear, Plum, and Florican Raspberry
- Interested in growing day-neutral strawberries in a sheltered environment? Check out this UMN publication.
Apples
Growth stage update: Tight cluster
Images: Zestar!® (left) and Rave®/First Kiss® (right) shown here in “tight cluster” growth stage, where floral buds are beginning to be exposed, but are still tightly grouped. Photo (left) taken at Northwoods Apple Orchard in Olmsted County, Minnesota (04/15, Zone 5a) and photo (right) at the University of Minnesota Horticultural Research Center (04/29, UMN HRC; Zone 5a, photo taken by Kate Scapanski, UMN Researcher).
The next major apple growth stage after 1/2 inch green is called tight cluster, in which apple floral bud tips are visible, yet tightly compact, as surrounding leaves continue to mature. In fruit production, critical temperatures are temperature thresholds that signify when damage to buds from cold or freezing temperatures begins. For the tight cluster phase, research has shown that 10% of apple buds will likely die when temperatures lower to 27°F, and 90% of buds will likely die at 21°F. Fortunately, most regions in Minnesota where apples are currently at the tight cluster stage are not expecting to reach temperatures near or below the critical threshold. Refer to the Midwest Fruit Pest Management Guide on page 13 to learn more about which insect pests can coincide with tight cluster.
Pest highlight: European red mite (ERM; occasional pest) + Beneficial arthropod highlight: Predatory mites
Images: (Right) Managing European red mite (ERM) overwintering eggs is an approach to keeping populations under control. ERM eggs are most effectively managed at the apple ½ inch green growth stage. Left photo credited to University of Georgia Plant Pathology.
Introduction:
Of the three different pest mites that can affect apple orchards, European red mite (ERM, Panonychus ulmi) can be one of the most problematic. ERM are spider mites, about 0.42 mm in length, and reddish-brown in appearance. Their host range primarily covers plants in the Rosaceae, or rose family, which includes apples.
ERM overwinter as eggs on or near tree buds and fruiting spurs before they hatch in the spring. After the first adult generation of the growing season matures, females begin to lay eggs on leaves around the time of petal fall. ERM populations complete several generations throughout the growing season. Their pest habits are unique as their populations and activity often decrease in the middle of the summer due to natural enemy activity and hot, dry conditions. ERM target apple leaves, leading to a stippling injury that reduces photosynthetic activity and leaf bronzing, which can result in smaller fruit sizes.
Note on predatory mites:
Before discussing solutions for managing ERM, it is important to understand that many mite populations, even when present, can be less damaging when populations are balanced in the presence of predatory mites. There are a number of predatory mite species that exist (ex. Neoseiulus fallacis, Amblyseius andersoni, and Typhlodromus pyri). Many predatory mites are about the same size as a spider mite, with a more pear or oblong body shape and lighter color.
A “balanced” predator-to-pest mite ratio in an orchard is an estimated ratio of 1 predator mite for every10 pests mites to keep pest mite populations at low, non-damaging levels. To protect and cultivate predatory mite populations, avoid applying broad spectrum pesticide products like pyrethroids, organophosphates, and carbamates that can be toxic to predatory mites, especially early in the season.
Scouting and management:
Scouting and management:
Eggs:
Growers can scout for ERM overwintering eggs from late fall until early spring, where their small red eggs can be found near dormant apple buds and fruiting spurs. One effective way to manage ERM at this stage is to use a dormant oil that smothers overwintering eggs, where applying a delayed dormant oil spray at the ½ inch green stage has been shown to be most effective. The Midwest Fruit Pest Management Guide also recommends increasing the oil concentration (1-2%) at this stage.
Adults:
If ERM is not managed at the egg phase, adult populations can be scouted for and managed after petal fall or later. Scouting instructions during this time of the year are based on taking a number of leaf samples and checking their undersides for the presence of mites. The number of leaves with mites is then divided by the total number of leaves, and that percentage is used to make a management decision (to be covered in more detail in a future Fruit Update), where the threshold to act is lower earlier in the season. Because ERM have up to eight generations per growing season, practice early management of ERM beginning populations that have met the action threshold to prevent serious outbreaks. Refer to the Midwest Fruit Pest Management Guide on pages 17-19 for chemical options for post-petal fall ERM management.
Article section resources:
Predatory mites. (University of Maryland Extension)
European red mite (University of Utah Extension).
European red mite life history (YouTube; Cornell University)
Managing mites in apples (PowerPoint slide deck; Ohio State University)
Infographic: Early-season grape diseases are often managed proactively before infections occur. Above are the top five fungal pathogens to be aware of during early-season management. Growers should take note that symptoms may vary in their appearance based on the degree of infection and the grapevine growth stage and varietal type, among other factors.
In the Upper Midwest, where rainy springs and humid summers are common, grapevine foliar and fruit diseases become a large part of vineyard management plans. There are a number of different diseases which infect grapes, some that can more severely affect fruit quality and crop yield. While the symptoms, or the visual results, of these infections may not immediately appear or seem to progress to the point of concern, many pathogens do begin infecting plants early in the season between the period of bud break and berry set, especially during and after rain events. Because of this, it’s recommended to take a proactive approach to managing grapevine foliar and fruit diseases because post-infection treatments are often limited in options and their effectiveness. The five main pathogens managed during early-season vineyard management include: 1. Phomopsis cane and leaf spot (Phomopsis viticola), 2. Anthracnose (Elsinoe ampelina), 3. Downy mildew (Plasmopara viticola), 4. Black rot (Guignardia bidwellii), and 5. Powdery mildew (Uncinula necator).
Removing infection sources:
Many pathogen spores overwinter in fruiting bodies (similar to microscopic mushrooms) on remaining fruits, mature shoots (i.e. canes), and older wood (i.e., old spurs, cordons, and trunks). Proactive, cultural management starts with removing infected materials away from a vineyard, or destroying them on site to reduce the total spore count in the vineyard. This includes removing mummified grape clusters and pruning wood, which can be burned or repurposed off-site. Growers may also consider removing wild grapevines growing near the perimeters of a vineyard as they can passively host various diseases.
Pruning and canopy management:
How well grapevines are pruned and managed throughout the summer determines shoot density for each grapevine canopy, which impacts how well air flows throughout the canopy. Many pathogen spores benefit from low air flow and high humidity, or even long periods of leaf/fruit wetness to produce an infection. Thus, following up pruning with early season shoot thinning also ensures adequate shoot density.
Growers can scout for ERM overwintering eggs from late fall until early spring, where their small red eggs can be found near dormant apple buds and fruiting spurs. One effective way to manage ERM at this stage is to use a dormant oil that smothers overwintering eggs, where applying a delayed dormant oil spray at the ½ inch green stage has been shown to be most effective. The Midwest Fruit Pest Management Guide also recommends increasing the oil concentration (1-2%) at this stage.
Adults:
If ERM is not managed at the egg phase, adult populations can be scouted for and managed after petal fall or later. Scouting instructions during this time of the year are based on taking a number of leaf samples and checking their undersides for the presence of mites. The number of leaves with mites is then divided by the total number of leaves, and that percentage is used to make a management decision (to be covered in more detail in a future Fruit Update), where the threshold to act is lower earlier in the season. Because ERM have up to eight generations per growing season, practice early management of ERM beginning populations that have met the action threshold to prevent serious outbreaks. Refer to the Midwest Fruit Pest Management Guide on pages 17-19 for chemical options for post-petal fall ERM management.
Article section resources:
Predatory mites. (University of Maryland Extension)
European red mite (University of Utah Extension).
European red mite life history (YouTube; Cornell University)
Managing mites in apples (PowerPoint slide deck; Ohio State University)
Grapes
About grapevine foliar and fruit diseases and early-season management.
Infographic: Early-season grape diseases are often managed proactively before infections occur. Above are the top five fungal pathogens to be aware of during early-season management. Growers should take note that symptoms may vary in their appearance based on the degree of infection and the grapevine growth stage and varietal type, among other factors.
In the Upper Midwest, where rainy springs and humid summers are common, grapevine foliar and fruit diseases become a large part of vineyard management plans. There are a number of different diseases which infect grapes, some that can more severely affect fruit quality and crop yield. While the symptoms, or the visual results, of these infections may not immediately appear or seem to progress to the point of concern, many pathogens do begin infecting plants early in the season between the period of bud break and berry set, especially during and after rain events. Because of this, it’s recommended to take a proactive approach to managing grapevine foliar and fruit diseases because post-infection treatments are often limited in options and their effectiveness. The five main pathogens managed during early-season vineyard management include: 1. Phomopsis cane and leaf spot (Phomopsis viticola), 2. Anthracnose (Elsinoe ampelina), 3. Downy mildew (Plasmopara viticola), 4. Black rot (Guignardia bidwellii), and 5. Powdery mildew (Uncinula necator).
Removing infection sources:
Many pathogen spores overwinter in fruiting bodies (similar to microscopic mushrooms) on remaining fruits, mature shoots (i.e. canes), and older wood (i.e., old spurs, cordons, and trunks). Proactive, cultural management starts with removing infected materials away from a vineyard, or destroying them on site to reduce the total spore count in the vineyard. This includes removing mummified grape clusters and pruning wood, which can be burned or repurposed off-site. Growers may also consider removing wild grapevines growing near the perimeters of a vineyard as they can passively host various diseases.
Pruning and canopy management:
How well grapevines are pruned and managed throughout the summer determines shoot density for each grapevine canopy, which impacts how well air flows throughout the canopy. Many pathogen spores benefit from low air flow and high humidity, or even long periods of leaf/fruit wetness to produce an infection. Thus, following up pruning with early season shoot thinning also ensures adequate shoot density.
Additional practices like exposing fruit clusters by removing basal leaves, as well as secondary and lateral shoots near the cluster zone are ways to encourage faster cluster drying after rain events and increase exposure to any organic or conventional fungicide products applied.
Fungicide programs:
Both conventional and USDA Organic-approved fungicides are available to proactively manage and, in some cases, treat grapevine diseases. Grapevine conventional fungicide programs are thoroughly covered in the Midwest Fruit Pest Management Guide starting at the bottom of page 157. Growers who manage their vineyard under USDA Organic standards may apply sulfur or copper products as a part of a fungicide program for grape varieties that do not exhibit sensitivity. Additionally, copper injury can occur under high temperature conditions, even if a specific variety is not considered copper-sensitive.
To further support the season-extension aspect of growing day-neutral strawberries, it can be advantageous to grow them under a shelter like a small-sized high tunnel, known as a caterpillar tunnel, or even low tunnels. Several Minnesota producers have implemented high tunnels to extend the season. The University of Minnesota has done research on the economic viability of high tunnel strawberry production in soil and in soilless media with fertigation (i.e., table top strawberry production).
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.
Fungicide programs:
Both conventional and USDA Organic-approved fungicides are available to proactively manage and, in some cases, treat grapevine diseases. Grapevine conventional fungicide programs are thoroughly covered in the Midwest Fruit Pest Management Guide starting at the bottom of page 157. Growers who manage their vineyard under USDA Organic standards may apply sulfur or copper products as a part of a fungicide program for grape varieties that do not exhibit sensitivity. Additionally, copper injury can occur under high temperature conditions, even if a specific variety is not considered copper-sensitive.
For successful management, take time to understand fungicide classifications in order to prevent fungicide resistance among pathogens. The Midwest Fruit Pest Management Guide lists fungicide general effectiveness against various pathogens, along with other important information that can be found on product labels.
Note: Information in this publication regarding pesticide use is for educational purposes only.
Images: Upper left: tart cherry in early white bud (photo taken at Firefly Berries, Olmsted County, Zone 5a, 04/29); lower left: pear in white bud surrounded by emerging vegetative growth; middle photos: plum in bloom with expanding vegetative buds (lower photo); right: a fruiting lateral emerging from summer-bearing raspberry cane (photos taken at Sekapp Orchard, Olmsted County, Zone 5a, 04/29).
To learn about critical temperatures that impact buds for some of these fruit crops (e.g., pear, peach, apricot, plum, cherry) visit the Critical Temperatures web page from Washington State University. Additionally, the publication, “Growth stages in fruit trees- from dormancy to fruit set” shows growth stages for other tree fruit crops.
Note: Information in this publication regarding pesticide use is for educational purposes only.
Additional fruit crop growth stage updates: Tart cherry, Pear, Plum, and Florican Raspberry
Images: Upper left: tart cherry in early white bud (photo taken at Firefly Berries, Olmsted County, Zone 5a, 04/29); lower left: pear in white bud surrounded by emerging vegetative growth; middle photos: plum in bloom with expanding vegetative buds (lower photo); right: a fruiting lateral emerging from summer-bearing raspberry cane (photos taken at Sekapp Orchard, Olmsted County, Zone 5a, 04/29).
To learn about critical temperatures that impact buds for some of these fruit crops (e.g., pear, peach, apricot, plum, cherry) visit the Critical Temperatures web page from Washington State University. Additionally, the publication, “Growth stages in fruit trees- from dormancy to fruit set” shows growth stages for other tree fruit crops.
Interested in growing day-neutral strawberries in a sheltered environment? Check out this UMN publication.
Day-neutral strawberries differ from the more traditional June-bearing strawberries because they can be harvested continuously from the start of bearing until the end of the growing season. Day-neutral strawberry transplants are also planted/replaced yearly, more similar to an annual crop. Day-neutral strawberries can have a market advantage by having a strawberry crop to sell after the June-bearing strawberry season has finished, especially when consumers understand the uniqueness of these off-season sales. One of the most commonly grown variety in Minnesota is Albion, which has a reputation for balancing yield with fruit quality. Other varieties include Cabrio, Portolla, and Seascape.To further support the season-extension aspect of growing day-neutral strawberries, it can be advantageous to grow them under a shelter like a small-sized high tunnel, known as a caterpillar tunnel, or even low tunnels. Several Minnesota producers have implemented high tunnels to extend the season. The University of Minnesota has done research on the economic viability of high tunnel strawberry production in soil and in soilless media with fertigation (i.e., table top strawberry production).
Day-neutral strawberry information:
- Growing organic day-neutral strawberries in caterpillar tunnels
- Growing day-neutral strawberries in high tunnel table-top systems
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.
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