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Recently in the Fruit Category

The following list is updated with links to new and revised online Extension publications as they become available. 

June 17, 2014

General/Curiosity Insects (NEW!)
A new addition to the Extension Y&G diagnostic tool "What insect is this?" Find information to help identify and understand insects (1) with obvious wings (flies, wasps, moths, etc.) and (2) insects without obvious wings (beetles, bugs, ants etc.).

May 27, 2014

Carpenter ants (revised)
Bronze birch borer and twolined chestnut borer in Minnesota (revised)
Maple petiole borer
Nightcrawlers (revised) 

December 2, 2013

Pest management in the home strawberry patch (new)
Pest management for home blueberry plants (new)
Integrated pest management for home raspberry growers (new)
Integrated pest management for home stone fruit growers
Leafminers in home vegetable gardens

August 26, 2013

Masked hunters (revised)
Fourlined plant bug in home gardens (revised)

July 16, 2013

"Annuals" have been added to What's wrong with my plant? diagnostic tool.

June 18, 2013

Root maggots in home gardens (new)
Emerald ash borer in Minnesota (revised)
The Extension EAB web page has also been revised

May 23, 2013

Anthracnose (revised)
Powdery Mildew
Cedar Apple Rust and Other Gymnosporangium Rusts
Crown Gall (revised)

Managing Apple Scab on Ornamental Trees and Shrubs
Managing Impatiens Downy Mildew in the Landscape (new)

Managing Impatiens Downy Mildew in Greenhouses, Nurseries, and Garden Centers
Basil Downy Mildew

May 1, 2013

Aphids on Minnesota Trees and Shrubs (revised)
Woolly Aphids on Minnesota Trees and Shrubs (revised)
Spotted Wing Drosophila (new)
Two-spotted Spider Mites in the Home Garden and Landscape (new)

Written by Laura Marrinan, University of Minnesota student
HORT 1003 Horticulture for the Home Garden, Spring 2014

Kiwi is a tasty treat that is typically thought of as a tropical or warm climate fruit. However, Minnesota gardeners can get in on the action as well. The practice of growing kiwi in Minnesota has been around since University of Minnesota's Professor Samuel Green began growing cold-hardy varieties in 1892.kiwifruit.jpg

According to Drs. James Luby and Emily Hoover from the University of Minnesota's Department of Horticultural Science, kiwifruit in Minnesota needs to be one of the following species: Actindia kolomikta 'Arctic Beauty', A. arguta 'Bower Berry', or A. polygama 'Silver Vine' (2). These cold hardy kiwifruits don't look like the fruits you typically pick up at the grocery store. They are hairless, skinless and generally have a much higher sugar content. These fruits are also usually about the size of a grape. A. kolomikta can be grown successfully in most areas of Minnesota because it can survive in USDA Hardiness Zone 3, while A. arguta and A. polygma, both are most successful in the central and southern part of the state, USDA Plant Hardiness Zone 4 (2).

Starting your kiwifruit
Kiwi vines can be found at many retail nurseries during the growing season, according to Luby and Hoover. To produce fruit, one male plant is needed for every six female plants. The female plants produce the berries while the male plants are the source of pollen. To differentiate the plant sexes look for at the structure of the plant and the size. The female blossoms have a center pistil to receive the pollen and are usually twice as large, according to an article by horticulturist Victoria Lee Blackstone (1). The male plant will also typically have much larger flowers than the female. Depending on your location, some varietals will be more successful than others (see chart). A. kolomikta is the top performer throughout Minnesota because of its hardiness. This is also a variety that will taste fairly similar to commercially available kiwi (2).


According to Luby and Hoover, there are multiple components to consider when starting your own kiwifruit vines. The ground must be fairly sloped and shaded from the afternoon sun. This will help keep the fruit in a moist, cool soil that is preferred by the vines. To help retain moisture, the soil can be covered with wood chips, leaves, or pine needles. This can also help control weeds, retain a consistent temperature and promote healthy roots. Although the soil needs to retain moisture, it is also important to choose a site that is well-drained and porosity (2).

The soil should have a pH of neutral to slightly acidic, around 5.5-7.5 (2). U of M Soil Test Lab Kiwifruit will also benefit from a fertilizer containing nitrogen and the chloride form of potassium. The recommended analysis of fertilizer for kiwifruit is 33-0-0, or 33% nitrogen, 0 % available phosphate and 0% soluble potash. This fertilizer should be applied from spring until early July.

Kiwi vines require support. They grow upward in a counter-clockwise direction, so using a pole or trellis will help direct the growth (4). Fencing will also help the vines grow in the proper direction and provide support.

Winter Protection
Protecting kiwifruit during Minnesota winters is important. The onset of winter comes with two major issues for these vines: animals and weather protection. In Minnesota, cottontail rabbits can cause extensive damage to plants when they are looking for food in early winter. Fencing your vines will help prevent hungry rabbits from damaging your plants (2). Rabbits and Trees and Shrubs

Proper shading of the plants is important because of all the direct sunlight and the sun reflected off of the snow. Slipping a burlap sack or spiral wrap over the trunks will help protect your vines from sunscald (4).kiwi wraps.jpg


(1) Blackstone, V.() Differences Between Male & Female Kiwi Vines. SF Gate.

(2) Luby, J., & Emily, H. (2010, September 10). Plant and Site Selection. Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from

(3) Kiwifruit Berries. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from

(4) McKenzie, J., & Emily, H. (2007). Hardy Kiwifruit in Minnesota Gardens.Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from

(5) Trunk Wraps. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from

Spotted wing Drosophila found in Minnesota again

Jeffrey Hahn, Extension Entomologist

One of the bigger garden questions last year was whether we would see spotted wing Drosophila (SWD) again in 2013.  SWD flies are invasive insect pests that damage a variety of thin-skinned fruit crops, such as raspberries, blackberries, strawberries, cherries, plums, blueberries, and grapes.

Jeff Hahn

Photo 1: Female spotted wing Drosophila on blackberry. It lacks the dark spot on its wings that males have.

Unfortunately, the answer is yes.  The University of Minnesota and Minnesota Department of Agriculture (MDA) have detected and confirmed the presence of SWD in Minnesota this year.  The first confirmed report of SWD this year occurred on June 27 when a male SWD was found in a vineyard in Dakota County.  SWD was then verified on July 3 in summer raspberries in Rice County.  There have also been fly specimens suspected to be SWD in several other counties not only in the Twin Cities area but also in Greater Minnesota.  You can go to the MDA web page to check for updated information on where SWD has been found.  Last year, the first SWD was found in August.  Eventually, SWD was confirmed in 29 counties in Minnesota.

SWD looks very similar to the small fruit flies you might see flying around overripe fruit on your kitchen counter.  They are about 1/8th inch long, yellowish brown with red eyes.  The male is fairly easy to identify; look for a dark spot near the tip of the wing.  Unfortunately, the female lacks this spot and is difficult to identify without high magnification.  The larvae are cylindrical in shape, tapering at one end.  They are legless, whitish and very small, no more than 1/8 inch long.  However, if you find fruit fly adults or larvae associated with healthy fruit, there is a very good chance it is SWD; other fruit flies are typically associated with overripe and rotting fruit.

If you have potentially susceptible fruit in your garden, consider putting out vinegar traps to try to detect SWD so you have some warning if they are present in your garden.  If you do find SWD, be sure to harvest ripe fruit frequently.  Remove and dispose of any overripe or rotting fruits.  You can also use insecticides to help protect your fruit.  Target the adults though, as there is not any practical solution one fruit is infested by the larvae.  The only option is to properly destroy the fruit so the flies cannot finish their development.

For more information on SWD management, see the publication Spotted wing Drosophila in home gardens.

If you believe you have SWD, especially in a county where it is not been confirmed, contact the Minnesota Department of Agriculture "Arrest the Pest" hotline by email at or leave a voicemail at 1-888-545-6684. 

Jeffrey Hahn, Extension Entomologist

Jeff Hahn

Photo 1: Spotted wing Drosophila is one of the pests attendees will learn about at the Fruit and Vegetable Pest First Detector workshop.

It is not too late to sign up for the Fruit and Vegetable Pest First Detector Workshop. If you have an interest in fruits and vegetables and want to learn more about new and emerging invasive pests and pathogens that are threatening Minnesota, then consider signing up for this half day program. This workshop, put on by the Minnesota Department of Agriculture (MDA) and the University of Minnesota Extension, is scheduled for Wednesday, July 24 at the MacMillan Auditorium at the Minnesota Landscape Arboretum. Check in starts at 8:00 a.m. and the program begins at 8:30. The workshop ends at noon.

This workshop is appropriate for anyone with an interest in fruit and vegetables, including home gardeners. Attendees will learn how to identify invasive pests and distinguish them from common look a likes. They will also find out the proper steps to take if they suspect you have found and invasive pest.

Attendees have the option to become a First Detector volunteer. First detectors are a local resource to help state officials respond to calls made to the Arrest a Pest Hotline. First Detectors are volunteers trained to help citizens diagnose and report possible infestations of invasive species to the Minnesota Department of Agriculture. First Detectors are a part of the National Plant Diagnostic Network (NPDN) First Detector Program which promotes the early detection of invasive plant pathogens, arthropods, nematodes and weeds.

For more information, see the Minnesota Fruit and Vegetable Pest First Detector web page. To register, go to the Minnesota Landscape Arboretum web page.

Karl Foord - Extension Educator, Horticulture

Apple maggots are predicted to emerge in the beginning of July so this is a good time to consider protective strategies.

Karl Foord

Photo 1: Apple fruit prior to thinning

Apple maggot flies recognize and identify apples through a series of visual and chemical clues. The red sphere traps and the yellow square traps both covered with a sticky substance as well as scented lures aid in capture of apple maggot flies and will indicate their presence. However, it is unlikely that such traps will effectively protect your apples.

Karl Foord

Photo 2: Apple fruit after thinning

I have tried plastic bags which can work although they make the tree look phantasmagorical (i.e. nightmarish - please forgive - I always wanted to use that word in a sentence). I have also found that they can collect water and if faced toward the south can heat up and cause damage to the apple skin.

Karl Foord

Photo 3: Apple fruit with maggot barrier I

So this year I am trying Maggot Barriers that I purchased from the Seattle Tree Fruit Society although there are other suppliers of this product that can be found on the web. The Seattle Tree Fruit Society web site does show pictures of their recommendations for attaching the barrier. The maggot barriers are the so called "footies" which serve as single use protective socks that can be used to try on shoes if you have no socks.

Karl Foord

Photo 4: Apple fruit with maggot barrier II

The maggot barriers may confuse the flies who no longer recognize the apples because of the different color and texture of the footie covering the apple. The barriers may physically inhibit the maggots from depositing their eggs under the skin of the apple. However, mosquitoes don't seem to have any problem getting their proboscis through our woven shirts, so I wonder if apple maggot flies would really have a problem getting their ovipositor through the mesh of the footie.

Karl Foord

Photo 5: Apple fruit with maggot barrier III

This is the procedure that I am using. First thin the flower to one fruit per cluster (Photos 1 & 2). Then slip the sock/barrier over the apple and secure with a rubber band. I have three examples: the first with the apple at the end of the sock (photo 3), the second with the apple in the middle of the sock (photo 4), and finally the apple with most of the sock above the apple (photo 5). (note the last photo was taken with a flash which is why the color is so different)

I will let you know how this works for me.

For more information on apple maggot including other methods of control please use the following link. apple maggot

Strawberry Growers take Note!

Karl Foord - Extension Educator, Horticulture

Removing straw mulch on strawberries using lilac buds as an indicator

Sometimes nature is a better indicator of the best time to take action than our measuring equipment. Researchers Terry Nennich and Dave Wildung attempted to determine the best time to remove the straw mulch on strawberries using growing degree days (GDD) which are a measure of heat accumulation. GDD are often used to predict when a plant might flower, or how developed a pest might be to optimize the timing of control.

Karl Foord

Photo 1: Buds of Common Lilac (Syringa vulgaris)

In this case Terry and Dave found complications that made GDD a less reliable indicator for the timing of mulch removal. Given this they looked for other signs in nature that might be more useful. Their conclusion was that when the lilac buds open, it is time to take off the straw. This correlated well with the end of strawberry dormancy. Timing is critical as a delay in removal was shown to reduce both the total yield and the size of berries. The longer the delay the greater the loss in yield.

To this end please observe the pictures of bud break in common lilac (Syringa vulgaris) in photo 1 and in dwarf Korean lilac (Syringa meyeri 'Palibin' in photo2. Both taken May 6, 2013 in Chaska, MN.

Karl Foord

Photo 2: Buds of Korean Lilac (Syringa meyeri 'Palibin')

Is it time to remove the straw mulch from your strawberries? What is the status of the lilac buds in your neighborhood?

Flowering Plant Video Library - Fruit Trees

Karl Foord - Extension Educator, Horticulture

Click on the link to see the video with host Dr. Mary Meyer, Professor of Horticulture

Sour Cherry, Pie Cherry (Prunus cerasus 'Northstar')

Karl Foord

Photo 1: Sour Cherry (Prunus cerasus 'Northstar')

Canadian Serviceberry (Amelanchier canadensis)

Karl Foord

Photo 2: Canadian Serviceberry (Amelanchier canadensis)

Grapes (Vitis spp.)

Karl Foord

Photo 3: Grapes (Vitisspp.)

Apples I: Dwarfing Rootstock and Pruning (Malus domestica)

Karl Foord

Photo 4: Dwarf Apple (Malus domestica)

Apples II: Pest Management (Malus domestica)

Karl Foord

Photo 4: Pears (Pyrus communis)

Pears (Pyrus communis)

Michelle Grabowski, UMN Extension

JAR Y&G.jpg

N. Gregory, UDEL,

Photo 1: Sporulating gall of Japanese apple rust on juniper

Cool wet spring weather stimulates galls of several rust fungi (Gymnosporangium spp.) to produce bright orange gelatinous spore producing structures that readily catch a gardeners eye. Several species of Gymnosporangium rust fungi are native to Minnesota and infect eastern red cedar trees, Juniperus virginiana during part of their lifecycle and trees and shrubs from the Rosaceae family during a different part of their lifecycle. Native Gymnosporangium rusts include cedar apple rust, quince rust, hawthorn rust and juniper broom rust. Photos and descriptions of these plant diseases can be seen at the UMN Extension online plant diagnostic tool What's wrong with my plant?

A new Gymnosporangium rust has recently been found in the United States but not yet in Minnesota. Japanese apple rust is caused by Gymnosporangium yamadae. This fungus does not infect Minnesota's native red cedar trees but does infect Juniperus chinensis and J. squamata. Both of these species of juniper are sold as ornamental trees or shrubs here in Minnesota. Although Japanese apple rust is unlikely to cause any serious damage to junipers, this fungus also infects apple trees. At this time, it is unknown how the apple varieties grown in Minnesota will respond to Japanese apple rust.

To identify Japanese apple rust in juniper, look for round woody galls that are 1/2 to 1 inch in diameter. When wet, these galls become covered in a 1/4 inch thick layer of orange gelatinous goo. As this spore filled goo dries, it will become apparent that they arise from short orange projections, like small shelves sticking out from the side of the gall. In contrast, the native cedar apple rust galls produce orange gelatinous tentacles that swell to 1-2 inches long when wet.

If you suspect a juniper in your area has Japanese apple rust, please contact the Minnesota Department of Agriculture by sending an email to or leave a voice message at 888-545-6884. The MDA will contact you with further information in 1-2 days.

Frost Protection of Blueberry Flowers

Karl Foord - Extension Educator, Horticulture

Irrigation serves to protect blueberry flowers from frost damage.

Here are some pictures - explanations to follow:

Brad Munsterteiger

Photo 1: Frost protection of blueberry flowers by irrigation

Brad Munsterteiger

Photo 2: Frost protection of blueberry flowers by irrigation

Brad Munsterteiger

Photo 3: Frost protection of blueberry flowers by irrigation

Frost Damage to Apple Flowers

Karl Foord, Extension Educator, Horticulture

Temperatures in the mid to low 20's were encountered last Tuesday April 10th in many parts of central and southern Minnesota. Apple fruit flowers are damaged at temperatures lower than 28 degrees F. depending on the stage of the flower bud and the length of time at the low temperature. The more open the flower bud the more susceptible the bud is to low temperature damage.

The following picture gallery shows the types of frost damage experience by apple flowers in Chaska, Minnesota. The gallery begins with heathy flowers with green stigmas and cream anthers, shows partially damaged flowers with dead stigmas and soom dead anthers, and finally a flower will all parts killed.

Karl Foord

Photo 1: Healthy Apple Flower

Karl Foord

Photo 2: Healthy or partically damaged apple flower

Karl Foord

Photo 3: Totally damaged flower top left and partially damaged flower bottom right

Karl Foord

Photo 4: Frost killed apple flower with brown stigmas and anthers

Karl Foord

Photo 5: Frost killed apple flower with brown stigmas and anthers

A Look at the New USDA Hardiness Zone Map

A hardiness zone map (HZM) provides information that gardeners and professional horticulturalists use in determining which herbaceous and woody perennial plants will survive cold temperature in a particular geographic area. Last week the United States Department of Agriculture released a new hardiness zone map to replace the older 1990 version.

As with past maps, the new map:
  • is a visual representation of average annual minimum temperatures across the United States. Data points used to create the map were the lowest daily minimum temperatures recorded at thousands of temperature data stations during each of the years sampled.
  • divides the U.S. into multiple hardiness zones with 10o F differences in average annual minimum temperatures. Zone 1 is the coldest zone (-50o F to -60o F).
  • divides each hardiness zone into "a" & "b" with "a" being the colder half of any zone and "b" the warmer half.

There are changes in the new map and the process that was used to develop it:


    Photo 1: 1990 USDA Hardiness Zone Map

  • The 1990 HZM was based on data from a 12-year period (1976-1990) while the new HZM is based on data from a 30-year period (1976-2005).
  • The data used to create the new map was more complete, and a complex algorithm was used to interpolate between recording stations. Temperature data from more than 8000 temperature data stations belonging to the National Weather Service, the USDA Natural Resources Conservation Service, the USDA Forest Service, the Bureau of Reclamation, and the Bureau of Land Management was used. Average minimum temperatures were then calculated for ½ mile square computer grids for the entire country to create the new hardiness zone map. This was followed by a review process that included climatologists, agricultural meteorologists, and horticultural experts who checked for errors, looked for the source of errors, and corrected errors.


    Photo 2: 2012 USDA Hardiness Zone Map

  • The new map is Geographic Information System-based. This means that the map is more accurate, is interactive (by zip code) to improve user experiences, and has higher resolution that can show smaller areas of zone delineations than before. While the 1990 map was a static image and was not designed for web use, the new map allows users to zoom in to a local area to see the higher temperatures of cities that are heat sinks, the lower temperatures on mountain tops, and the buffering effects of large bodies of water on temperature.

What does the new hardiness zone map show?
In general, the new map shows what we have all been experiencing in recent history: warmer low temperatures during winter. A shift of ½ of a zone was common for much of the country. Closer to home, here is what happened to Minnesota's hardiness zone map:


    Photo 3: 1990 USDA MN Hardiness Zone Map


    Photo 4: 2012 MN Hardiness Zone Map

  • There was a ½ zone shift for much of the state because Minnesota, like the rest of the U.S., has been experiencing warmer annual minimum temperatures during the time period used to create the new HZM.
  • Zone 5a (with average minimum temperatures of -15o to -20o) crept up into the south central portion and the far southeastern corner of Minnesota.
  • Much of the southern ½ of Minnesota that was formerly divided into zones 4a & 4b is now zone 4b (with average minimum temperatures of -20o to -25o).
  • The four pockets of Zone 2b (with average minimum temperatures of -40oto -45o) disappeared from northern Minnesota.
  • The amount of Minnesota that is zone 3a (with average minimum temperatures of -35o to -40o) shrank significantly due to an increasing area of zone 3b (with average minimum temperatures of -30o to -35o).
  • Parts of the far northern shore of Lake Superior that were formerly zones 4b and 4a are now designated as 4a and 3b, meaning they are colder.

What kind of impact should the new hardiness map have on Minnesota gardeners?

  • We can all rest easy knowing that the warmer minimum annual temperatures we have been enjoying over the past years really did happen!
  • Remember that a HZM is created based on average annual minimum temperatures and should only be used as a general guide. By the very definition of average, we know that temperatures lower than the average minimum temperature of the zone you live in will occur. Pick your plants accordingly. Maybe we can broaden the palette of plants we choose to grow in Minnesota a bit, but be cautious and wise in your weighing of risk vs. gain as you trial new plants. Losing an herbaceous perennial or quickly-maturing shrub to winter injury may be of little concern in terms of the time it takes to establish a replacement plant. Losing a slow-growing shrub or a tree that takes decades to grow to mature size creates more pain.
  • Hardiness zone maps are of no help in predicting plant damage or mortality during acclimation and deacclimation. Remember that hardiness is not just about the lowest temperature a plant must survive during a winter. Every year, starting in late summer, perennial plants goes through a multi-month process called acclimation that prepares them for winter survival. In spring dormant plants go through a reverse process called deacclimation that restores their ability to actively grow during the growing season. Plants can be winter-injured or killed by abnormally low temperatures during the months of acclimation and deacclimation too. This is especially true of marginally hardy plants from warmer parts of the country or world that we may try to grow in Minnesota.
  • Hardiness zone maps provide gardeners with one category of plant performance information: winter survival. Good plant performance is not just about winter survival. If the new HZM persuades you to plant cultivars and species new to you, remember that there are other selection categories to consider as you match a plant to your planting site: soil texture, soil moisture, soil pH, light exposure, precipitation, etc.

Winter Squash: Easy to Grow and Good for You

Mary H. Meyer, University of Minnesota Professor and Extension Horticulturist

Image Source's Name

Squash and pumpkins can store for several months, if harvested at maturity and properly cured. (Click to enlarge.)

I love winter squash! So with the more than 100 kinds grown at the Arboretum this past summer, it was fun looking at the huge variety and deciding which ones I would try cooking this winter. I settled on 8 'new-to-me' kinds: orange hubbard, fairytale pumpkin, autumn crown, Queensland blue, marina di chioggia, rouge vif d'etampes or cinderella pumpkin, crown, large world of color blend, and 1 'old' favorite: blue hubbard, see photo below. You can still find winter squash at the markets and you can make plans this winter to grow your own squash next summer. Winter squash are easy to grow, have high nutritional value, and some kinds store well for several months. If you can still find open Farmer's Markets, you will likely have a much better selection of squash and pumpkins than the one or two kinds available in the supermarket.

Pumpkin and winter squash were cultivated by the American Indians for centuries and are native to North America. Pumpkin is derived from the French word pampion meaning "sun-baked squash", which was modified to pompkin and finally to pumpkin.

What is the difference between a pumpkin and squash?

The scientific name of most pumpkins, and acorn, delicata, and spaghetti squash is Cucurbita pepo; these fruits have very hard stems or petioles, which cannot be dented with your fingernail.

Winter squash usually has a softer, wider, pulpy stem or petiole, which you can penetrate with your fingernail. Most of the large fruited types, the HUGE award winners, 'Boston Marrow' and 'Mammoth' are Cucurbita maxima, along with many kinds including buttercup, kabocha and hubbard squash.

The third species is the buff-colored butternut squash, these oblong beige fruits are Cucurbita moschata, and are excellent for baking and pies. This species is usually sold as canned pumpkin.

Mary Meyer

The 2011 pumpkin and squash display in the Great Hall at the Minnesota Landscape Arboretum.

Although all kinds of pumpkin and squash are edible, they vary in consistency, texture, color, and flavor. Some may have flesh that is several inches thick with a small seed cavity, while others are thin fleshed with large seed cavities, making them inefficient to process and bake.

What squash or pumpkin is best to grow in Minnesota?

Most winter squash and pumpkins can be grown and mature successfully in Minnesota, especially central and southern areas. In general, the larger the fruit, the longer the growing season required. Any variety that matures in 100 days or less should produce mature fruit in Minnesota. Varieties that need 120 days will likely be successful only in the southern portion of the state. Most are direct seeded in the field. It is important to know the days to harvest for the varieties you are considering.

Winter squash require full sun, plenty of space for their long vines, and adequate moisture. After growing to maturity on the vine, harvest fruit before any injury from frost. Although appearing to be tough and firm, all curcurbits are tropical plants and do not do well in cool or cold weather; frost can damage the fruit and prevent the rind from curing properly and long storage.

After harvest, clean the rind with a soft cloth to remove any soil. Store the fruit at 80° to 85°F with 75 to 80% relative humidity for approximately 10 days to cure the fruit. Curing heals wounds, helps ripen immature fruit, enhances color, and insures a longer post-harvest life. Curing is beneficial in pumpkins and some winter squash, but 'Butternut,' 'Hubbard,' and 'Quality' squashes have not shown any added benefits from curing. Curing is detrimental in Acorn types, and will hasten senescence. After curing, the fruit can be stored at 50-55 degrees but no cooler, and it can be held at room temperature if 50-55 is not possible. Store cut pieces in the refrigerator.

Immature fruit will not fully develop indoors. Fruit that is mature green, may ripen further indoors but will not have as high nutritional value, or flavor. Color change is often important, as most squash and pumpkins turn from green to orange, beige, blue, pink or yellow, at maturity.

Nutrition and Cooking

While all squash and pumpkins are edible, some have more sugar and flavor. If the fruit is fully mature, it will remain firm and can actually improve in storage, for 3 to even 6 months, if the rind has been cured properly and is not bruised. Acorn squash is an exception; it is not a 'good keeper' and should be used within a month of harvest. Cucurbita pepo, true pumpkins, acorn and spaghetti squash have long fibers and some cooks prefer winter squash because they are non-fibrous. Regardless of the type, cooking is similar for all squash or pumpkins, however, the large ones are much more difficult to handle and peel. By far the easiest way is simply by cutting the fruit in half, removing the seeds and baking it cut side down. Rubbing the edges with olive oil, or butter prevents adhering to the pan.

Winter squash is a good source of complex carbohydrates and fiber. Research suggests that the soluble fiber in foods such as squash can play an important role in reducing colon cancer. Winter squash is also a source of potassium, niacin, iron and beta carotene. Usually, the darker the orange color, the higher the beta carotene content. Beta carotene is converted to Vitamin A, which is essential for healthy skin, vision, and bone development. The nutrient content of winter squash can vary, depending on the variety, maturity and condition of the fruit. The following information is a summary of all varieties, cooked, baked and cubed:

Nutrition Facts (1 cup cooked, cubed)
Calories 80
Protein 1.8 grams
Carbohydrate 18 grams
Dietary Fiber 5.8 grams
Calcium 28.7 mg
Iron 0.67 mg
Potassium 895 mg
Folate 57 mcg
Vitamin A 7,291.85 units

I have vine borers in my squash, how can I control them?

Vine borers are difficult to control effectively with insecticides. You can reduce potential damage the following season by disposing of infested plants. Vining types of squash can be encouraged to root at the nodes, giving the plant some ability to withstand attacks of vine borers. Some success in control of an active infestation may be achieved by carefully splitting open areas being fed upon and removing the larvae. Late planting of short maturing squash, planting after July 1, after which the adult has laid its eggs, may avoid borer damage.

North Carolina State:
A beautiful book on squash: Goldman, A. 2004. The Compleat Squash: A Passionate Grower's Guide to Pumpkins, Squashes, and Gourds. Workman Publishing.

Disease Resistance of Cold Hardy Grapes

Michelle Grabowski, UMN Extension Educator

Clemson University - USDA Cooperative Extension Slide Series,

Photo 1: Anthracnose on grape berries

New research published in Plant Health Progress provides Minnesota grape growers with more information about disease resistance of cold hardy grapes. Canadian researchers tested several cold hardy cultivars of wine grape for resistance to Anthracnose. Anthracnose, a disease caused by the fungus Elsinoe ampelina, can infect leaves, tendrils, shoots, and immature berries of grape vines. Leaves have dark brown to black spots. As leaf spots grow, the center of the spot turns gray to white and eventually falls out. Leaves may appear peppered with small shot holes. Anthracnose lesions on stems and petioles are sunken oval spots that almost look like hail damage, but the edges Anthracnose spots will always be black. Berries infected with anthracnose have brown to black spots with a pale white center. These spots are often described as 'bird's eye' spots.

Anthracnose thrives in warm, wet weather. In Minnesota, some vineyards see Anthracnose every year, and others rarely have a problem says University of Minnesota Grape Breeder Dr. Jim Luby. The Canadian researchers found Frontenac and Frontenac Gris to be resistant to anthracnose, Frontenac Blanc and La Crescent to be susceptible, and Marquette to be highly susceptible. Growers interested in trying new wine grape cultivars should learn about disease resistance to several grape diseases in addition to anthracnose. Downy mildew, black rot, powdery mildew and Botrytiscan all be problematic in Minnesota vineyards. More information about disease resistance and culture of cold hardy grapes can be found at the University of Minnesota Cold Hardy Grape webpage.

The Ultimate in Disappointment - a Mealy Peach

Karl Foord, UMN Extension Educator

The fresh peach season is upon us, and there are few things as bad as the anticipation of a delicious peach only to discover that the flesh is mealy and mostly inedible. I have been burned enough by mealy peaches to be wary of buying them in grocery stores. It is extremely difficult to look at a peach and determine whether the flesh is mealy. This makes peaches a risky purchase because you never know whether you will be delighted or disappointed. This article addresses two topics; 1) how you can improve the chances of not getting a mealy peach, and 2) how does peach flesh become mealy?

Carlos H. Crisosto, Department of Plant Sciences, UC Davis

Top: Flesh browning. Bottom: Healthy peach.

The best way I know to reduce the chance of buying a mealy peach is to reduce the time from farm to your house as well as the number of transfer points that the peach travels through in getting to you (Figure 1). One way to do this is to purchase fruit in bulk from a local Pick-Your-Own (PYO) farm that will deliver fruit direct from a peach grower in Michigan. The farmer contacts these entities when the peaches are ready. A truck is procured and the peaches travel to a central PYO and from there to your PYO where you are called to pick up the peaches. The peaches can get to you in a matter of days.

Explaining how a peach becomes mealy requires understanding the fruit distribution process and the physiology of the peach. Peach flesh becomes mealy if a physiologically immature peach is placed in cold storage or a physiologically mature peach is stored at suboptimal temperatures. To avoid the first problem, peaches are harvested and then "conditioned" at 68°F for 24 hours to ensure that all are physiologically mature. To avoid the second problem, following conditioning the peaches should be chilled to between 32° and 37°F and kept in this range throughout the processes taking the peach from farm to retail store. At the retail store the peaches can be brought back to 68°F where they can ripen in a 4 to 6 day range at which point they will be ready-to-eat.

Peaches stored in the 38° to 51°F temperature range develop mealy brown flesh and ripen inconsistently. Peaches stored in the 31° to 34°F temperature range with 90% relative humidity can maintain quality for two weeks or more. If peaches are exposed to temperatures at or below 30°F, their tissues will be damaged by freezing.

Carlos H. Crisosto, Department of Plant Sciences, UC Davis

Mealy peaches.

If the most likely cause of mealy peaches is storage in the 38° to 51°F temperature range and we are still buying mealy peaches, then somewhere in the shipping and distribution process the peaches are experiencing this temperature range. This could be because it is difficult to maintain this cold chain or because of the great variety of fruits and vegetable being shipped, compromises must be made during transport. Not all fruits and vegetables have the same optimum storage temperature. Apples and peaches do well at 32°F, whereas grapefruit like 50° to 60°F, lemons like 45° to 48°F and the temperature optimum for oranges depends on where they come from. California oranges have a different temperature optimum (45-48°F) than Florida (32-34°F) which has a different temperature optimum than Arizona and Texas (32-48°F).

As a scientist it would be interesting to know where the system breaks down, however as a consumer I just want to find the easiest way to get a great tasting peach.

Ask your Pick-Your-Own farmer if they purchase Michigan Fruit for sale through their business.

L. Kitinoja and A. A. Kader, Postharvest Horticulture Series No. 8E, Postharvest Technology Research and Information Center, University of California, Davis 2002.

Late Leaf Rust on Raspberry

Michelle Grabowski, UMN Extension Educator

M.Grabowski, UMN Extension

Photo 1: Late Leaf Rust on Red Raspberry

Bright orange powdery spots on red or purple raspberry leaves are symptoms of late leaf rust, a fungal disease caused by Pucciniastrum americanum. This pathogen can also infect individual druplets in the fruit, turning them into small bright orange powdery masses on an otherwise delicious looking fruit. Late leaf rust needs to alternate between raspberry and white spruce trees. It does not survive on raspberry plants from year to year. Removing nearby white spruce trees is not an effective way to control this disease, however, as spore can travel long distances on the wind. High humidity in Minnesota this summer has favored infection with late leaf rust.

Lydecker/BlackIce™ Plum: A New Plum for the Midwest

Brian Smith, UWRF

Photo 1: Lydecker® BlackIce™ Plum. 'Oka' ( Prunus besseyi x P. salicina) x Z's Blue Giant (P. sal.).

Emily Dusek, University of Wisconsin River Falls

Plums have long been regarded as a fruit that can be grown in the Midwest, but the size and quality has never measured up to that of California's plums. Well we Midwesterners need not lament anymore because the new Lydecker/BlackIce™ Plum (bred by Dr. Brian Smith from University of Wisconsin-River Falls) exhibits many of the characteristics of Californian Plums all while being a winter-hardy plum!

This was achieved because the BlackIce™ was bred from a flavorful Californian plum (Z's Blue Giant) and a winter hardy plum (Oka). With this combination of genes, the BlackIce™ has a dark purpley-black tender skin, with rich juicy red flesh on the inside, and free-stone pit that does not stick to the flesh. All while being winter-hardy to as low as -35 ºF (Zone 3b) and ripening 2 to 3 weeks earlier then any other large quality plum for the Midwest!

Brian Smith, UWRF

Photo 2: Lydecker® BlackIce™ Plum. 'Oka' ( Prunus besseyi x P. salicina) x Z's Blue Giant (P. sal.).

In addition to an earlier ripening period and larger sized fruit (5cm x 5cm), the BlackIce™ exhibits many other positive characteristics, such as being naturally semi-dwarf in size and only growing to about 10' tall and 8' wide. It also has a weepy growth habit, which gives the BlackIce™ an interesting appearance in the winter and spring--but its main attribute is its ability to produce California-like plums in the Midwest.

To get the optimum yield of these tasty plums, it is necessary to plant another cultivar of compatible genetic background with the same bloom-time so cross-pollination can occur. This is because plum trees are self-infertile, and for successful pollination to take place there needs to be another plum within 50 feet. The preferred pollinator for BlackIce™ is Toka, but if there is a late bloom season for the BlackIce™ either 'Compass' or 'Alderman' plums will suffice.

it is very important not to apply any insecticide to your trees while they are blooming because otherwise the bees will not be able to carry the pollen from one tree to the other to pollinate your flowers so they can develop into fruit!

Photo 3: Black knot on a plum tree.

When growing fruit, it is crucial to monitor for pests. In regards to insects, the BlackIce's™ problems include scale, plum curculio, cat-facing insects and peach tree borer, the best control for any pest is always sanitation. So remember to remove all of your dead plant debris from the ground! In addition to good sanitation, it is also necessary to have a spraying regime in place to prevent and control all insects. The BlackIce™'s disease susceptibility is average to above average. It is still moderately susceptible to brown rot and black knot, which are fungal diseases that are also best controlled by the removal of all plant debris from the ground, and pruning off of any infected areas. And fungicide applications should be done just before bloom/early bloom, mid-bloom, and late bloom. Luckily, BlackIce™ is more tolerant than its Japanese-American hybrid counterparts to bacterial spot.

Once these simple control measures are in place, the enjoyment you receive from planting, growing, and eating these sweet plums will be boundless. For with these multiple attributes of color, and firmness combined with the winter hardiness necessary to survive harsh winters and short-growing seasons it is evident that BlackIce™ has the potential to bring the fresh taste of California to our very own backyards.

Editor's note: A good article on cat-facing insects can be accessed at the Utah State University Cooperative Extension.

Emily Dusek graduated with an A.S in Horticulture from Century College in 2009. She is currently attending University of Wisconsin-River Falls to parlay her A.S. into a Bachelor's of Science. She has also received invaluable hands-on lessons working at Farrill's Sunrise Nursery in Hudson, Wisconsin. Emily first got into horticulture as just a baby; she has been told her first birthday present was a mini wheelbarrow and watering can!

Apple Sunburn

Photo 1: Sunburn necrosis of apple.

Karl Foord, UMN Extension Educator

Sunburn to apples should be distinguished from sunscald. Sunscald is damage to the bark of the tree when strong winter sun warms up tissues on the south facing side of the tree. When the sun sets, the temperature plummets and this softened tissue is damaged by freezing.

Sunburn is damage to the peel of the fruit. The temperature of the apple peel can be significantly greater than the ambient temperature ranging from 18°F to 29°F above ambient temperature on a clear day when other conditions are favorable (Schrader et al., 20011). Factors influencing peel temperature include solar irradiation, air temperature, relative humidity, wind speed and direction, and tree vigor.

Photo 2: Sunburn necrosis of apple.

David Bedford, a research scientist at the University of Minnesota Horticultural Research Center, noted seeing a lot of this type of damage due to the high temperatures and high dew points experienced this summer.

There are two types of sunburn damage, necrosis and browning. Sunburn necrosis involves the thermal death of the tissue and occurs at 126 ± 2°F (Photos 1 & 2). Sunburn browning describes the presence of a yellow, bronze, or brown spot on the sun-exposed side of an apple and occurs at peel temperatures between 115 to 120°F.
Proper pruning use of shade cloth and application of particle films are methods that growers can use to protect fruit and avoid sunburn.

Thanks to Janelle Daberkow, horticulture educator in Stearns and Benton counties, and the Benton County Master Gardeners for providing photos.

¹Schrader, L. E., Zhang, J., and Duplaga, W. K. 2001. Two types of sunburn in apple caused by high fruit surface (peel) temperature. Online. Plant Health Progress doi:10.1094/PHP-2001-1004-01-RS.

Construction of an Apple Tree

Karl Foord, UMN Extension Educator

Most apples trees today consist of an upper part, the scion, and a lower part, the rootstock, to which the scion has been grafted (Exhibit # 1). The scion produces the apples with which you are familiar such as Honeycrisp or Haralson. The rootstock confers a number of important traits on this 'compound' plant such as precocious flowering and size reduction. A tree on its own rootstock would produce a full sized 25' high tree and could take 6 to 7 years to flower. A dwarfing rootstock can reduce the size by 50% or more and reduce the time to flowering to 2 or 3 years. Size reduction makes more efficient use of space and facilitates numerous operations such as picking, pruning, and spraying. Rootstocks confer other traits on the plant such as disease resistance, stress tolerance, and ability to tolerate low


Thus apple breeding and improvement efforts must not only create and test scions for fruit quality and disease resistance, but also create rootstocks that have the desired dwarfing qualities, cold tolerance, and favorable reaction with the scion. To this end many rootstocks have been created with different degrees of dwarfing. The standard is a tree on its own rootstock which will be a full sized tree. Dwarfing rootstocks are classed by the percent reduction in size conferred by the rootstock relative to a tree on a seedling rootstock (Exhibit # 2). The size variation can range from a tree you could grow in a large pot on rootstock P22 to a full sized tree on a seedling rootstock. Exhibit #'s 3 and 4 show tree size variation conferred by three commonly used rootstocks.

All well and good but how is such a tree produced? A bud from a cloned version of the original tree is T-bud grafted on a cloned version of the original rootstock. In August a dormant bud in the axil of a leaf from the scion say Zestar!TM is harvested from trees pruned in such a way as to produce a lot of these kinds of buds. A T shaped cut is made on the rootstock tree about six inches above ground level, and the bud is inserted to pair the cambium cells of both materials. The cut is wrapped with a paraffin tape and left to overwinter. In the spring when the bud breaks the rootstock tree is cut above the graft and the scion becomes the upper part of the tree. This process is described in greater detail with very illustrative pictures in the following document:

The rootstock is also produced in a fascinating way. A cloned rootstock tree is planted and allowed to grow for a season and then is cut off at ground level. The next season a number of sprouts will arise from the rootstock and have the appearance of a bush. These branches are then mounded with sawdust covering around 10 inches of the new stem. The stem will develop roots between the uncovered part of the stem and the covered part still attached to the stump. At the end of the season the sawdust will be removed and the stems cut from the stump and the new shoots with roots will be planted as a new tree ready for the T-bud graft. These mounded layers are called stool beds.

If you go to buy an apple tree, purchase one where the scion and rootstock are both identified on the plant label. It used to be that the label on apple trees for sale would only indicate the scion and not the rootstock. At a big box store, I recently saw trees with labels that only indicated that it was a fruit tree. The label did not even identify the tree as an apple let alone as a Honeycrisp on M26. There is a big difference between Zestar!TM , Honeycrisp, and Haralson apples and as you now know a big difference between the rootstocks on to which they are grafted. To purchase a tree labeled in this fashion would be like buying a pepper plant and then waiting to see if it was a sweet bell pepper or a jalapeno.

All exhibits created by Karl Foord.

What are your apples doing right now?

Karl Foord, UMN Extension Educator

What are your apples doing right now?
Apple trees have two kinds of buds; vegetative buds that only give rise to leaves and shoots, and mixed buds that give rise to flowers as well as shoots and leaves. The parts of the flower in their primordial state can be identified in the dormant mixed bud as seen in this cross section (Figure 1).


Bud stages

Apple flower buds progress through a series of developmental stages. This begins with the Silver Tip stage where the bud has started to open but no green tissue is visible. The progression runs through to petal fall and the beginning stages of development of the apple fruit (Figures 2 - 10).






Apple varieties can break bud at different times, and buds can be at different stages on the same tree. For example, the buds on my Haralson apple tree are almost all between ½ inch green and tight cluster. Only the leaves are visible but the tips of the leaves are red. My Honeycrisp has a few buds beyond the ½ inch green stage like the Haralson, but many of the buds are between silver tip and green tip.

Bud sensitivity to temperatures

As we move into May and watch our apple flowers develop, what temperatures should we recognize as damaging to apple flowers? The temperature at which flower buds are injured depends to a significant degree on their stage of development. Buds are most hardy during the winter when they are fully dormant. As they begin to swell and expand into blossoms, they become less resistant to freeze injury. The temperature sensitivities of the bud stages noted previously are listed in Table 1.


The month of May can bring some damaging low temperatures. On May 9 of last year a low temperature of 25oF was reached in many locations in Minnesota. The apple flowers of many trees were in full bloom and vulnerable to temperatures below 28°F. In some orchards the frost damage to the flowers was practically complete and the whole apple crop was lost except for some late flowers on Honeycrisp and a significant number of flowers on Sweet 16, a late flowering variety.

At the present developmental stage, apple flower buds in Minnesota could survive temperatures in the low 20's. Let us hope we have seen the last of the temperatures listed in table 1, for this year at least.

Photo credits:

Hand Pollination of Apple Trees?

Karl Foord, UMN Extension Educator


Business Week.

I recently attended a conference on native pollinators presented by Jennifer Hopwood of the Xerces Society. The Xerces Society (founded in 1971) has worked to conserve invertebrates and their habitat by focusing on conservation policy, advocacy, education, and research.

One rather alarming topic presented at the conference involved Maoxian County in the Chinese province of Sichuan (see map). In this region farmers have been forced to pollinate their apples and pears by hand because there are insufficient natural insect pollinators to ensure proper fruit set and thus a crop. These are high value crops that must be free of cosmetic defects to be marketable. To achieve this, the growers have resorting to spraying when there is the least hint of a problem. This has resulted in marketable material, but at the cost of having destroyed all the native pollinators in the region. There are beekeeping services but these individuals hesitate to locate their bees in the area because of the danger presented to their hives by the pesticide use strategies of the fruit producers. The result hand pollination by humans. This report comes from one county in a province that produces a little more than 1% of Chinese apples. Nonetheless, the province still produces some 409,000 metric tons of apples (in 2009). And this pollination problem is not an isolated case, but rather extends to other countries in the region such as Pakistan, India, and Nepal.


Hand pollination in China.

Such a situation does not translate well into American agriculture especially considering labor wages. If we were to do so it would look like this: It takes twenty Chinese workers working for 10 hours to pollinate a half acre (see pictures). Translated into an orchard in the United States where the workers were paid $9 per hour, it would cost the growers $3,600 in pollination services. This would probably double the cost of apples.

How can we best relate to this situation? A certain amount of the problem comes from an ignorance of the complexities involved in the relationships between insect pollinators and crop plants. However, we in the U.S. are not immune, even though the problems we face may be different. Our commercially managed honeybee populations are facing a number of challenges as noted by Dr. Marla Spivak in a previous article. We have also seen a dramatic decline in a number of native bumblebee species that were previously quite numerous. The exact causes for such a decline have not been definitively identified, however it is likely that there is no one cause but rather a series of causes. And again the complexity we face with biological systems rears its head.


Map of China's Provinces.

Hand pollination of fruit crops is about as unsustainable as a system can get. The fact that it exists anywhere sends me a strong signal to be extremely vigilant about land management, pollinator habitat, and pesticide use to avoid such an outcome in our fruit production systems.


Pollination problems in China

Status Review of Three Formerly Common Species of Bumble Bee in the Subgenus Bombus

Thaddeus McCamant

In November, the stores were running low on Minnesota Honeycrisp and started replenishing the shelves with Honeycrisp shipped from Washington. For a while, my local grocery store had Minnesota and Washington Honeycrisp in the same bin. At the time, a friend complained to me about some apples he had recently bought. "I don't even think they are Honeycrisp," he told me, "the store must be selling red Delicious."

Even before he brought me an apple, I told him that they were Honeycrisp, but they were raised in a low elevation area of Washington.

I always get a little defensive when people use Delicious as the ultimate example of a bad tasting apple. Some of the best apples I have ever eaten were Washington Delicious. Twenty years, ago, I worked with about thirty apple orchards along the Washington-Oregon border. Some orchards were planted in the true desert near the Columbia River, while others were high in the foothills of nearby mountains. While testing the quality of the different apples, I quickly noticed that red Delicious and Golden Delicious grown in the desert were large and soft, while those grown in the mountains were smaller, crisper and had better overall flavor. When buying apples for myself or as gifts, I often bought Delicious grown near the mountains.

Certain varieties, like Granny Smith and Fuji, taste great when raised in areas with hot, dry summers. Other varieties taste better when grown in areas with cooler summers, like the foothills of the mountains. For cool season varieties like Delicious and Golden Delicious, elevation influences firmness, sugar content and the sugar acid balance. Granny Smith from the desert are firm and have a mouth-puckering supply of acid. The sugar/acid balance of cool season varieties can be adversely affected by climate.

Honeycrisp was developed in Minnesota and became very popular because it stays crisp long, has a high sugar content, and a moderate acid content. Honeycrisp has a little more acid than Delicious or Fuji, but less than Granny Smith. The sugar/acid balance of Honeycrisp is critical, because a Honeycrisp with no acid tastes just like a bland red Delicious.

My friend gave me one of his apples. It was a Honeycrisp, with the characteristic round shape and red/yellow color pattern, but the apple tasted as bad as Delicious apples that had been stored for a year and were being sold for $0.75 a pound. The apple was soft. I measured its sugar content at 11 % (11°Brix). The Honeycrisp I have measured in Minnesota usually have a sugar content greater than 15%. The acid content was low, making an apple with a dismal sugar content taste even blander.

Studying the influence of climate on apple quality was easy along the Washington-Oregon border, because nearly all the variability was due to elevation. High elevations have cooler nights. Where nights are cool, fruit is smaller and firmer. When we compare fruit quality of apples grown in Washington with those grown in Minnesota, there are a host of factors that could influence flavor: soil, daytime temperatures, humidity, sunlight intensity as well as nighttime temperatures.

With so many factors influencing the quality of apples, we cannot say for sure why Honeycrisp grown in Minnesota taste better than those grown in other climates. I can, however, go to a grocery store where Minnesota and Washington Honeycrisp are displayed together and pick out the Minnesota apples. The color pattern is slightly different on the Minnesota apples. When buying fruit for my family, I am very picky. I have no problem paying good money for good fruit, but I would not pay $0.75 a pound for the Honeycrisp my friend gave me.

Wine makers and wine consumers have known for centuries that wine tastes different depending on where the grapes were grown. Apple quality also appears to vary depending on where the apples were grown, and apples are grown over a much broader range of climates and soils than grapes. Apple consumers should also start becoming as particular about where their fruit was grown as the wine drinkers.

Thaddeus McCamant has been a Specialty Crops Management Instructor at Northland Community and Technical College in Thief River Falls Minnesota, and has fifteen years of experience in the fruit industry.

What's Happening in the Orchard?

Special thanks to Karl Foord and Apple Jack's Orchards for putting together the "What's Happening in the Orchard?" video series.

Midseason Apple Tasting

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

Winter Damage in Apples

Karl Foord, UMN Extension Educator

Preparation for winter

Plants acclimate or develop hardiness to freezing temperatures in response to changes in light duration and temperature. Acclimation is a two-stage process. The first stage is initiated by decreasing day length and results in partial hardiness. The second stage is initiated by subfreezing temperatures and results in full hardiness and acclimation. The hardening response in a plant may vary from year to year because of variation in temperatures over that year. The degree of cold hardiness of a plant is determined by the genetic capacity of a plant to acclimate to freezing temperatures and transform its tissues from a non-hardy to a winter hardy state. Plants are often given a cold hardiness rating based on the lowest midwinter temperature that plant tissues can endure relative to the USDA winter hardiness zone temperature bands. For example, Honeycrisp has a winter hardiness rating of USDA hardiness zone 3 (-40 to -30 F).

However, extreme low temperature is only one of a number of factors affecting winter survival. Winter damage frequently occurs during late fall or early spring due to extreme changes in temperature when the plant is not at its maximum hardiness. Injury is a function of the acclimation status of the plant at the time of the radical temperature change, and is often difficult to determine, and may not show for several years.

No two winters are the same

Every winter may have an episode that could cause some damage to some trees. For example the winter of 2008-9 was considered to be a more stressful year than the winter of 2009-10. This is borne out by the temperature graphs of the two years. Note that the winter of 2008-9 had a great deal of significant temperature fluctuation while 2009-10 was much smoother (Figures 1 & 2). Dr. Jim Luby noted three potentially damaging events that stand out in the winter of 2008-9 as follows: 1. The 43 degree temperature drop on December 15, 2008, 2. The 37 degree temperature drop on March 11, 2009, and 3. The five nights of low temperatures below - 20 from January 13 - 17, 2009. Many areas experienced a freeze event on Mother's Day (May 9, 2010) with varying amounts of damage. Some Minnesota apple orchards lost almost all their apple flowers and reports from Iowa noted lots of damage with bark splitting off the trees.



Carryover environmental effects

A dry season or a particularly heavy crop can reduce the vigor of the tree and make it more susceptible to winter injury. As Kathy Zuzek would tell you a rose variety that is defoliated by black spot in July is more susceptible to winter injury then one that has not been defoliated.

Other influencers of hardiness

Lack of snow cover during the coldest period can lead to root damage.

Pruning apples before they have accumulated their full hardiness can set trees up for winterkill, especially so with cultivars that are less winter hardy. In general, pruning cuts are dehardening in the early winter and the larger the cut the more dehardening occurs. Prune fruit trees in late spring before the buds become active.

Orchard topography is important because it affects cold air drainage. Lower areas where cold air accumulates can cause frost to settle and damage trees.


High intensity sunlight on a sunny winter day heats up the south and southwest side of thin-barked young apple tree trunks causing the cells to come out of dormancy and become active. After sunset temperatures can drop precipitously to levels well below freezing which kills active cells and conductive tissue. This often appears as a longitudinal crack running up and down the trunk.

Commercial tree wraps made of crepe paper, plastic spiral wraps or longitudinally cut drain pipe will intercept the sun and insulate the bark preventing sunscald. Wrap the trees from base to the lowest branch in the fall after leaf drop. I have used all methods. I have left the plastic wraps on for at least three years until the bark thickens and is less prone to sunscald. I removed and rewrapped the crepe paper each year.

The Taste of Minnesota Apples - An Adventure

Karl Foord, UMN Extension Educator

I did an apple tasting exercise with 24 young people last summer and we tasted the following apples traditionally available at grocery stores, Granny Smith, Golden Delicious, Jonagold, Tentation, Fuji, American Cameo, Royal Gala, and Red Delicious. More then half of the young people chose Fuji as their number one choice. Given this array of apples my taste buds agreed with theirs.

Then I started tasting local Minnesota Apples. Quite frankly I was astonished. These were excellent apples and in my opinion outclassed all of the commercially available apples previously tested. Granted the store apples had either been grown in Washington State and stored for 10 months, or had been shipped from either Chile or New Zealand. The Minnesota apples were fresh. Certainly tastes differ significantly among people and a recommendation is simply my opinion. You must discover for yourself as it is your taste and opinion that will render the final decision.

We are still early in the apple season. Some of the earliest of varieties have come and gone like State Fair. This is mostly due to the warm spring we had. However, many of the best are yet to come. My favorite early apples are Chestnut Crab and Zestar. I thought Paula Red was a good apple when captured within its optimum taste window. It doesn't keep that well and that is why my memory of Paula Red is one of a mushy apple. Check out our Early Apple Tasting video with Mike Dekarski (linked to this Y&G issue) to see some early season apples that we tested last week.

I look forward to SweeTango but we will have to see how many apples make it to the market. I also look forward to Honeycrisp, Sweet Sixteen, and SnowSweet.

Don't miss out on the Minnesota fresh apple season. Most orchards will let you taste before you buy so you can get the apple that tastes best to you.

I highly recommend that you give yourself a treat and experience the taste adventures available in local Minnesota Apples.

You can find an orchard near you at the Minnesota Grown .

What's Happening in the Orchard?

What's Happening in the Orchard?

Karl Foord, UMN Extension Educator


Photo 1: Strawberry field showing some almost ripe berries and developing fruit.


Pick-your-own strawberries should be in full swing as of this writing. The picture below was taken at Apple Jack Orchards in Delano on June 10, 2010. Don't miss the opportunity to taste fresh strawberries. You can find a strawberry field near you by going to entering your location and clicking on the strawberry button. The Minnesota Grown Strawberry fields will be listed in order based on proximity to your location.


Continue to protect your small young apples. I found damage from a few green fruitworm as well as plum curculio. Plum curculio causes feeding and egg laying damage to young apple fruit. Practice sanitation and remove all infected fruit. Do not let the fruit fall to the ground permitting the curculio larvae to burrow into the soil pupate and come back next year in greater numbers.

Some minor damage by green fruitworm - a climbing cutworm. (Photo 5.)kf5.JPG

Photo 5: Damage to young apple fruit by green fruitworm.


Photo 6: Pine Tortoise Scale on Uncle Fogy Pine.

My roving garden camera also found Pine Tortoise scale in my Uncle Fogy Pine. The scales were so thick on this tree that it looked like the scales were the bark of the tree. Because plants contain low densities of the nitrogen compounds needed for building proteins, the scale needs to consume an excess of sap to satisfy their nutritional requirements. The excess is expelled as "honeydew" which acts as a substrate for the growth of a sooty mold fungus that blackens affected plants. My tree was stunted by the scale and blackened by the fungus.

Thanks to Jeff Hahn and Emily Hoover for identification of insect pests. Photos by Karl Foord.

What's Happening in the Orchard?

Karl Foord, UMN Extension Educator

As you know, this has been another unique spring for Minnesota. We started out several weeks ahead of normal and lost some ground with a cold spell. Unfortunately, in some areas the cold spell was more than a delay. In certain parts of the state the nighttime lows on May 9th reached 25.5 degrees F.


Strawberry flowers are most vulnerable to frost damage when fully open. At this growth stage 30 0F will damage the flowers. The fruit can tolerate a few more degrees and sees damage at and below 28 0F. A "popcorn" stage closed flower bud shows damage at 26.5 0F and a tight bud at 22 0F. A damaged strawberry flower will turn black in the middle whereas a healthy flower will be yellow in the middle (Photo 1). This frost damaged open flowers and some "popcorn" flowers. All is not usually lost with strawberries as they flower over a two to three week period (note the variation in stage from open flower to young fruit (Photo 2) and the healthy clusters of young fruit that survived the frost (Photo 3). Look for pick-your-own strawberries to be available the second or third week in June depending on your location. Experience strawberry flavors beyond those available in grocery stores where the plants have been bred for shipping at some cost to flavor.



It took a week to discern what damage these low temperatures had done to apple flowers. Unfortunately, fields with early flowering cultivars that experienced these temperatures were damaged (Photos 4 and 5).

There may be some apples available as only 10% of the flowers are needed to produce a full crop. Note the size advantage in fruit that can accrue from being the first flower in the cluster to open - the king flower (Photo 6).

If your apple flowers were not damaged by frost and you experienced good seed set, it will soon be time to thin. The tree will naturally drop a number of these apples in the so called June drop, but it is likely that you will still benefit from your own thinning. Thinning to one fruit per cluster or spur is recommended. Proper thinning promotes big apples and helps to avoid alternate bearing where you have a surplus of apples in one year and a surfeit the following year. Photos 7 and 8 show and apple flower/fruit cluster before and after thinning. Keep an eye out for leaf rollers (Photo 9) and plum curculio.



Fruits are forming on the first raspberry flowers (Photo 10). We may see the end of strawberry picking overlap with the beginning of raspberry picking.

Sincere thanks to Apple Jack Orchards for permission to photograph their plants. Also thanks to Mike Dekarski and Tom Marxen for their insights into strawberry, apple, and raspberry culture. Photo credits: Karl Foord.

Edible Landscape Wrap-Up

Emily Tepe, University of Minnesota Research Fellow, Department of Horticultural Science

After many weeks of harvesting mountains of chard, tomatoes, zucchini, peppers, cucumbers, raspberries and a multitude of other vegetables, fruits and herbs, the University of Minnesota Edible Landscape has been put to bed. Well...almost. The few lone stands of silvery blue kale seem to mock the cold, their leathery leaves sweetening with each frosty night. And many of the herbs are even holding onto their green. Other than those, the Edible Landscape is now resting after a long and productive season. snow on kale_tepe.JPG

Photo 1 (left and above): Snow on dinosaur kale in the University of Minnesota Edible Landscape on October 12, 2009. Emily Tepe.

If you haven't had a chance to see the gardens on the St. Paul campus this year, and if you haven't been following the Edible Landscape blog, here's a rundown of some of the details of the project. The Edible Landscape filled four beds outside the Plant Growth Facilities on Gortner Ave. The 1500 square foot garden was comprised of 75 varieties of fruits, vegetables, herbs and flowers. The garden was designed to emphasize the ornamental qualities of edible plants, and demonstrate how these plants might be incorporated into the home landscape in creative, attractive ways. Most of the ornamentals, herbs and warm season crops were started from seed in the greenhouse during the winter months. Others, such as chard, kale, summer and winter squash, melon, lettuces and radishes were direct seeded throughout the season. By mid-October, almost 500 pounds of produce had been harvested from the Edible Landscape and shared with students, faculty and staff in the Department of Horticultural Science.

After cleaning all the annuals out of the garden (which were then composted), winter rye seed was raked into the beds for a winter cover crop. It may sound strange to think of cover crops in a home gardening demonstration. After all, we normally think of cover crops being used on acres of land, not in the backyard. But cover crops in the home garden can offer great benefits such as weed suppression, erosion control, increased microbial activity and moisture retention, just to name a few. You can read about Green Manure Cover Crops for Minnesota on the U of MN Extension Website.


Photo 2 (right and above): The largest bed in the University of Minnesota Edible Landscape in mid-July. Emily Tepe.

If the idea of edible landscaping sounds intriguing, or if you would simply like to learn more about this project, visit the Edible Landscape blog. The entire season was documented on the blog, which is filled with photos, design ideas, plant lists, growing information and more. Now that the harvests have finished, and the season is being evaluated, there will be more discussions on the blog about plant combinations that worked well, successful varieties, and lessons learned. Read, learn, share and join the discussion.

Wealth of Education Found in the Display and Trial Garden

Emily Tepe, Research Fellow, Department of Horticultural Science

10-1-09ediblelandscaping_emilytepe.JPGIf you walk through the St. Paul campus Display and Trial Gardens these days you're bound to see a lot of activity. No, I'm not talking about bees on the flowers (although there were a lot of those with the unusual warm weather in September), I'm talking about students. With the start of the fall semester comes a plethora of courses on plant identification, propagation, diseases and insects. The Display and Trial gardens offer a convenient and valuable living laboratory for these courses. In fact, throughout the year (save for a couple of months in the depths of winter) these gardens offer education to many people in the University community and beyond.

Photo 1 (left): Edible landscape portion of the University of Minnesota Display and Trial gardens. Emily Tepe

An Inspiring Outdoor Classroom

The Display and Trial gardens are comprised of various areas between Alderman Hall (home of the Department of Horticultural Science) and the Plant Growth Facilities on Gortner Avenue. Trees, shrubs, and hardscaping create the foundation for the gardens, and break it up into beds, each with their own theme. These themes change from year to year as new varieties are introduced, student projects are realized, and interesting gardening styles bring an opportunity to explore and experiment. The 2009 season brought some inspiring plantings and great educational opportunities.

These educational opportunities often get started while there is still snow on the ground, as students propose projects for the garden and begin designing beds and planting seeds in the greenhouse. Classes ,such as Professor, Neil Anderson's Floriculture Crop Production, research and schedule their assigned crops, working backwards from the planned finish date (mid-May), to assure their annual flowers are at the perfect stage for judging before being planted out in the gardens. Many of the varieties they grow are trials for major seed companies.

When spring arrives, students who have proposed projects for the gardens, begin breaking ground, laying out beds, sowing seeds, and eventually setting out transplants. They are responsible for maintaining their plantings throughout the season, keeping the beds watered, weeded and looking good. It's a great experience for students to take what they've learned in the classroom and put it all into practice. These projects bring the fresh ideas of students to the forefront, allowing them to experiment with new concepts and interesting designs, and even showcase some of their research.


By the time the gardens are in full swing, the St. Paul campus is pretty quiet. Most of the student body is gone for the summer, and the gardens become an inspirational outdoor venue for summer camps, youth enrichment programs, Master Gardener events, and horticulture industry field days. 

Photo 2 (right): Master Gardeners tour the Edible Landscape at the University of Minnesota State Master Gardener Conference. Emily Tepe

On any given summer day you are bound to find a group of high school students cutting flowers for a design and marketing program, or a flurry of youth in matching t-shirts tending a plot of vegetables; kept on task by their nurturing and enthusiastic mentors. Members of the local community often visit the gardens to view the new varieties released by the University, the vast array of annual flowers, and the creative ideas such as this year's Edible Landscape.

A Living Laboratory

10-1-09PlaPathclass_EmilyTepe.JPGOnce classes start in September, University students begin spending a lot of time in the gardens. Many of the students in the introductory horticulture courses have never seen some of these plants before, and the gardens offer a close-up look at the topics they're studying. Tom Michaels, professor in the Department of Horticultural Science (teaching Plant Propagation this semester) said of the Edible Landscape portion of the gardens, "Students pass right by those beds every time they come to lab. They can't help but see examples of the food they buy in the produce department actually growing in front of them. It gives me the opportunity to talk about those foods and encourage them to stop by the beds and find examples of how chard differs from lettuce or dinosaur kale, or similarities and differences between beans and peas". The gardens are indispensable for the plant identification courses as well. Students find examples of hundreds of species, and with hand lenses and forceps, can scrutinize tiny flower parts to determine the plant family to which they belong.

Photo 3 (above): Plant pathology students observing symptoms of apple scab in the Display and Trial garden. Emily Tepe.

Horticulture students aren't the only ones spending time in the gardens. The Display and Trial Gardens provide a wonderful laboratory for plant pathology and entomology students as well. Todd Burnes, scientist in the Department of Plant Pathology, said numerous courses spend time in the gardens identifying and studying various plant diseases. While in the home garden, powdery mildew, leaf spot and white mold would likely prompt immediate action, here we aren't so hasty. The opportunity for students to observe the symptoms of diseases, collect samples and study them in the lab is worth a few ugly plants here and there at the end of the season. Entomology students roam the gardens, sweeping their longs white nets along the edge of the prairie strip, or carefully trapping unsuspecting insects on the zucchini flowers. Once back in the lab, they'll identify and study their specimens.

Photo 4 (below and right) : Powdery mildew on zinnias in the Display and Trial Gardens. Emily Tepe.10-1-09_Med_powderymildewonZinnia_EmilyTepe.JPG

It is truly amazing the wealth of education that can be found in a garden. Here on the St. Paul campus, the Display and Trial gardens offer many people a chance to get up close and personal with flowers, grasses, trees, fruits and vegetables. And whether in class or just wandering through, there are countless opportunities to discover. Every garden offers such opportunities for young and old alike.
Excerpts from Arboretum News, Judy Hohmann, Arboretum Marketing & Public Relations Manager

Zestar in bowl high res_David Hansen.jpgThe University of Minnesota's Horticultural Research Center (HRC) breeds northern-hardy apples. Twenty-six robust varieties of apples have been introduced in the marketplace thus far. Some of these apples will be available for tasting at the Arboretum's Oswald Visitor Center (see weekend apple tasting details below).  Apples for purchase will be available at the Arboretum's AppleHouse in early fall. After 20 years of research, testing, and cultivation, SweeTango® -- the offspring of Honeycrisp and Zestar parentage will burst on the scene this year with predictions over time to jostle Honeycrisp from its superstar perch.  Look for a limited supply of SweeTango® apples for sale at the Arboretum AppleHouse in early Fall.

Photo:  Zestar apples in bowl. David Hansen.

Weekend apple tastings

Sample and rate test apple varieties - each weekend features different apples. Drop in and complete a short survey, and talk with Master Gardeners. Your feedback is compiled for research scientists in the apple breeding program.

  • 1 - 3 pm on September 19 and 20, October 3 and 4; 10 and 11
  • Oswald Visitor Center, Great Hall

Arboretum AppleHouse opens

  • Tuesday, Sept. 1
  • The AppleHouse apple and garden market opens September 1. This is a great source for a variety of freshly picked apples from the trees of the Horticultural Research Center. Continues through October. Located at the intersection of Rolling Acres Road and State Highway 5, just over a mile west of the Arboretum.

® Minneiska apple

Garden Calendar for July


Contributor: David C. Zlesak, University of Minnesota Extension Educator

Recent rains throughout much of Minnesota have been much needed after the dry spring.  Continue to water plants as needed.  There are a lot of great tips on watering in the Water-Wise Gardening article in this issue.  Plants to especially pay close attention to for supplemental water include those growing in containers and those that have been recently planted and are still in the process of adapting to their new site and establishing a well-developed root system.

Caterpillars on Blueberries

Jeff Hahn, Asst. Extension Entomologist

There are several caterpillars that have been detected feeding on the leaves of blueberries recently. One species is the copper underwing, Amphipyra pyramidoides. This insect, also known as the pyramidal fruitworm, is bluish green with a thin yellow stripe running the length of its body along its sides and small whitish patches. It also possesses a conspicuous hump on the end of the abdomen and grows to about 1 ½ inches when fully grown. This caterpillar feeds on a wide variety of plants in addition to blueberry, such as trees (e.g. apple, basswood, maple, oak), shrubs (e.g. lilac, viburnum, and rose), and fruit including grape, raspberry, and currant.

You can also find forest tent caterpillars, Malacosoma disstria, in your blueberries. Also referred to as armyworms, these caterpillars are easily identified by their blue and black bodies, the distinctive white footprint shaped spots on their back as well as hairs that stick out along the sides of their body. These caterpillars are about two inches long when fully grown. Despite their name, they do not make conspicuous webs in trees. They commonly feed on many deciduous trees, including aspen, birch, maple, crab apple, apple, ash, oak, and elm.

Simple Steps to Productive Apple Trees


Emily Tepe, University of Minnesota Research Fellow

Apples in the Home Garden

If you’ve ever dreamed about harvesting fresh fruit from your garden, apples are a great option. Sure, they require a bit more care than a typical landscape tree, but with a little TLC you could be harvesting juicy, crisp apples right from your own backyard!

There are a few things to keep in mind when growing apples that will help you achieve bountiful harvests of high quality fruit year after year. First it is important to know that apples require cross-pollination to reliably set fruit. This means planting more than one kind of apple tree. Your choice of varieties will largely depend on your priorities. If one tree will give you all the fruit you need you may want to consider planting a disease resistant flowering crab apple, such as Indian Summer or Snowdrift, for cross-pollination. Crabapples and edible apples can successfully cross pollinate. These trees are used in commercial orchards because they bloom over a longer period of time than most eating varieties, ensuring complete overlap of bloom. This equates to greater pollination potential of all the flowers, leading to more fruit. (Ensuring complete pollination and greatest fruit set might not be necessary however, which will be covered later when we talk about thinning.) These crabapple varieties and many others produce a profusion of flowers in the spring, and will then set an abundance of pretty, though inedible pea- to cherry-sized fruit which will dangle on the trees through the winter and into the next spring.  Since the tissue of the apple fruit that we eat is derived from cells of the maternal parent tree, the apple that serves as the pollinator will not affect our fruit quality.

Michelle Grabowski, University of Minnesota Extension Educator

Photo 1: Fire blight canker on a young apple branch. Michelle Grabowski

This past summer, many Minnesotans noticed dead brown wilted leaves on apple, crabapple and mountain ash trees caused by the bacterial disease known as fire blight (Read Midsummer Trouble for Trees & Shrubs) Although symptoms of fire blight are most apparent in spring and summer months, one of the best times to manage this disease is right now.

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