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Extension > Yard and Garden News > August 2009

Friday, August 14, 2009

Farewell and Hello


Thumbnail image for David Zlesak Dear Yard and Garden News readers,



I am resigning from the University of Minnesota Extension to start a new 
position just across the border at the University of Wisconsin-River Falls (UWRF) as an assistant professor in Horticulture.  Leaving the University of Minnesota Extension is bittersweet because I truly love Extension and all the wonderful people I've gotten to know and the opportunities I've been very fortunate to be a part of.  The Yard and Garden News is one of them- first as a frequent author and then also as your editor.  I have loved interacting with those of you that have contacted me and the great fun it has been being on the lookout for additional authors that have interesting information and stories to share with us. At UWRF I'll have a teaching appointment working with undergraduate students.  I'll be teaching plant propagation, woody plant identification, introduction to plant science, nursery management, and hopefully also plant breeding.  I look forward to helping lay a strong foundation in our next generation of horticulturists and helping students connect to their unique passions within horticulture. 



I am very excited Karen Jeanette will be taking over as editor of the Yard and Garden News!! Karen and I were officemates in graduate school at the University of Minnesota and both earned our undergraduate degrees in horticulture from UWRF.  She is a passionate horticulturist and has very strong information technology skills.  She has been working with the national eXtension team to help pull together Extension horticulture resources across the nation and establish the unified horticulture component on the national site.  No matter where people are at in the country, they can go to this eXtension hub and get directed to pertinent and region-specific information regarding horticulture.  I look forward to all the great opportunities ahead for the Yard and Garden News with Karen leading the way.  The recent survey results from your evaluation of the newsletter will also be a great tool to help Karen keep the newsletter strong and continue in a way that meets your needs in even a greater way.


At the beginning of August the format of the newsletter changed to a blog.  There have been some questions that have come up because of that.  Many of you love to print out the newsletter to read it.  Many of us spend so much time at the computer that having a hard copy and being able to spend time in the yard or elsewhere as we read the newsletter is a treat. If you would like to more easily print the newsletter or just see it as a complete newsletter with each article in its entirety right after each other like it used to look there is a way.  Please go under the archives section on the right side of the page and click on the month you would like to view.  This should open a screen where all the articles in their entirety for that month are visible and printable. 


Thank you for the great opportunity it has been to serve you as a Yard and Garden News author and editor.


David C. Zlesak


Master Gardener Open House at UMore Park

UMore Park gazebo and annual flower bedsJoin Dakota County Master Gardeners and the University of Minnesota for a night of outdoor festivities at their 9th annual open house on Thursday, August 20th from 4 - 8 pm at the Dakota County Master Gardener Education and Research Display Gardens in UMore Park, 1605 West 160th Street in Rosemount.
Stroll through six acres of colorful educational and display gardens created and maintained by Dakota County Master Gardeners. Enjoy live music featuring steel drums while sampling wines created from the University of Minnesota grape introductions, free lemonade and fresh-cooked corn-on-the-cob, and assorted other treats for purchase. Bring in plant samples for analysis at the Plant Health Diagnostic Clinic, attend a Master Gardener mini-class on native plants, raingardens, herbs, plant propagation, or wildflowers for Minnesota, and visit interactive exhibits to learn about cow, turkey, honey bee, and other University of Minnesota agricultural research projects. Don't miss the University of Minnesota Raptor Center's live showing of native raptors such as owls, hawks, and eagles, or the wildlife exhibits from the DNR and Bell Museum. Check out the University of Minnesota Dairy and Meat Labs, the Chemopreventive Café, and the Historical Society. There will also be Junior Master Gardener activities for the children, horse demonstrations, and an appearance by Goldy Gopher.


Zowie zinniaThere is no cost to attend the Open House.  Bring the whole family and invite friends, neighbors, and co-workers for an evening of fun, food, music, entertainment, and education.

Visit the new Dakota County Master Gardener blog at http://www.dakotamastergardeners.org/ for a list of activities and highlights of the open house and other Master Gardener events at UMore Park.

The Dakota County Master Gardener Program is a community outreach program of the University of Minnesota Extension, with a mission to improve the quality of life and enhance the economy and the environment of the Dakota County community through education, applied research and the resources of the University of Minnesota.

Additional information about this event is available from Dakota County Master Gardener Coordinator Barbara Stendahl, stend004@umn.edu

Getting Hydrangeas to Turn Blue

David C. Zlesak and Gail Soens, University of Minnesota Extension Educator and Bailey Nurseries New Variety Coordinator / Section Grower Bud and Bloom Hydrangeas & Roses





Blue hydrangea in landscapeWith so few true blue flowering shrubs for our landscape, it is no wonder so many of us are drawn to the beauty of blue hydrangeas! Only one species of hydrangea we commonly see for sale and in our northern landscapes include cultivars that can be coaxed to bloom a true blue or, if desired, a pure pink. It is Hydrangea macroplylla which is also known as the bigleafed hydrangea. Endless Summer® is the most common cultivar of this hydrangea we see for sale in the north as it is able to bloom off of both old and new wood. This is unlike most other H. macrophylla cultivars which bloom on only old wood. Since this species is marginally stem hardy in zone 4, having the ability to bloom on new wood allows it to still flower in our climate even if the plant dies to the ground and needs to regrow from the base.



So, what makes bigleaf hydrangea turn blue , pink, or a shade in between?  The primary contributor is soil pH.  Soil pH ultimately influences the pH within the plant cells.  The critical part of the plant cells for pH and color are the large watery vacuoles within the bract cells (colorful portion around the small true flowers that look like petals).  The pH in the vacuoles influences the configuration and how light reflects to our eyes from the pigment anthocyanin.  Anthocyanin is a plant pigment that ranges in color typically between blue and pink and can appear cream or colorless in the transition between blue and pink.  The color the tissue appears depends on the pH of the cellular fluid and also other factors including presence and association of metal ions such as aluminum.  There are multiple anthocyanins and they all share a common core chemical structure and are distinquished by placement of side chains and sugars connected to the core structure.  Different anthocyanins have slightly different properties and color ranges.  Different plant species and even cultivars within a species can have a different types of anthocyanins and different relative concentrations. Anthocyanins generally appear more towards the blue end of their range when the cellular pH is more alkaline (or higher in number) and more pink when the cellular pH is more acidic or lower. 



Pink Endless Summer hydrangeaWhat???  Doesn't this seem counterintuitive and contradictory?  We have been told to lower the pH of the soil we have our hydrangeas planted in with elemental sulfur or aluminum sulfate to make the bracts turn blue and the opposite with lime or gypsum to make them turn pink.  Interestingly, the pH within the vacuoles of petal cells moves the opposite direction as the pH of the soil.  So, in order to raise the pH within the vacuoles of bract cells and make our hydrangeas turn blue, we actually lower the pH of the soil around our plants and visa versa for pink. 


Bailey Nurseries, the introducers of Endless Summer® produces tens of thousands each year and most of them are grown and sold with blue flowers.  There are actually three different cultivars in the series now and they all share the ability to bloom on both old and new wood.  There is Endless Summer® original, Endless Summer® Blushing Bride, and now the latest addition, Endless Summer® Twist and Shout.  For the Endless Summer® original being coaxed to turn blue, the flowers first appear white and then turn blue from the outside of the large colorful bract inward towards their middle until the whole bract is blue.  A question arose if it would be possible to make the petals color up and turn blue sooner (being white for less time).  Doing so would reduce production time.  In order to work towards answering this important question, we started by doing a series of bract pH tests to understand if bract pH is consistent during expansion and coloration or if it changes and is the trigger or somehow associated with when the bract can turn blue.



Endless Summer hydragea production at Bailey NurseriesWe collected mature and immature heads of Endless Summer ® original from plants grown to be pink and other plants being grown to turn blue.  We also collected heads of Endless Summer® Blushing Bride (it is a cultivar that has a little bit of blush to it and is stays primarily white).  Throughout our bract pH tests, we took a uniform amount of bract tissue and put it in distilled, deionized water.  We spun it at 14,000 rpm in a centrifuge. This very fast motion broke the cells and allowed the liquid content within cells to mix with the purified water.  After spinning in the centrifuge it was amazing to see the bracts holding their form, but appearing clear or white no matter what color they started as.  The solution then appeared the color of the bract before we spun it. We tested the pH of the solution with a standard pH meter.


We sampled fully expanded pink and blue bracts of Endless Summer® original.  The solution from the blue bracts had a pH of 6.10 and the pink bracts 5.94.  We also took immature florets of Endless Summer® original that were white at the base and their tips were starting to turn blue.  We cut a number of small florets separating the white bases from the blue tips and measured the pH of bract tissue of these different colors separately.  The white bases were a pH of 5.59 and the blue tips were 5.84.  Therefore, for the Endless Summer® original grown to be blue with low soil pH, we saw a clear transition in pH from 5.59 for the white base of an immature bract to 6.1 when the bract was fully blue and mature.  We didn't explore all the same stages and color transitions for Endless Summer® original grown to be pink.  This is something worth pursuing in the future.  It is interesting the pH of a mature pink floret was 5.94. This strangely happens to be a higher pH than that of the blue portion of a bract as it first began to turn blue (5.84). 



Closeup of endless summer hydrangea We also decided to look at the pH in Endless Summer® Blushing Bride.  This hydrangea does not turn blue or pink even when pH is altered.  It likely produces very little anthocyanin in general and therefore basically remains cream to white regardless of pH.   The sample taken from young expanding bracts of Endless Summer® Blushing Bride were a pH of 5.82 and the fully expanded florets were 5.96.  A trend of an increase in bract pH was also observed in Endless Summer® Blushing Bride as it matured. The pH of a mature bract of Endless Summer® Blushing Bride was intermediate of that of mature bracts of pink (5.96) and blue (6.1) Endless Summer® original. 


In the end this initial experiment helped us learn that there is a strong and clear association with blue bract color and bract pH in Endless Summer® original.  The blue color seems to go hand in hand with an elevated pH as it starts out white, begins to turn blue, and then matures as a stronger blue.  A subsequent  question we would like to answer is if anthocyanin is already present in the white bract tissue and cannot turn from white to blue until the petal pH is further elevated, or if anthocyanin is just not present in the white tissue yet and is synthesized at the point in bract development when we typically begin seeing blue coloration.  If the latter is true, it is likely that we cannot speed up blue coloration of bract tissue in Endless Summer® original.  The limiting factor in that case won't be the pH, but when anthocyanins are synthesized. 


The next steps in this study would be to directly test for anthocyanin pigment in different aged bracts to learn when it is synthesized as well as to possibly do some simultaneous tests growing Endless Summer® original hydrangeas in a range of different low soil pH's.  Growing plants in a range of different low soil pH's would be the most direct way to see the effect on coloring rate of florets based on soil pH and also to learn the effect of such pH levels on overall plant growth.


Sad Glads

Michelle Grabowski, University of Minnesota Extension Educator
Glad Fusarium wilt. Michelle Grabowski
This time of year gladiolus blossoms are a welcome sight, whether left in the garden or brought inside as a cut flower. Unfortunately not all gardeners will have gladiolus blossoms this year. A corm rot disease of gladiolus, known as Fusarium wilt has been found in Minnesota. This disease is caused by the fungus Fusarium oxysporum f.sp. gladioli. The last part of the fungus's name 'f.sp. gladioli' indicates that this fungus has a very narrow host range and will only cause disease in gladiolus and very closely related plants. This is good news for gardeners who have infected gladiolus plants mixed with other flowering annuals and perennials.

Gladiolus plants infected with Fusarium wilt are often stunted and do not produce flowers. The leaves first yellow, then turn completely brown and fall over. The fungus infects the corm of the plant, often starting at the basal plate where the roots attach. Gardeners may see dark spots on the outside of infected corms. When cut open, a reddish brown rot can be seen within the corm.

Thumbnail image for glad fusarium rot. Michelle GrabowskiIf Fusarium wilt occurs, completely remove all infected plants, including the corm. Destroy infected plants. Do not compost them. Save only firm healthy corms for next year. Rot can continue in storage so inspect corms before and after storage. Discard any discolored soft or crumbling corms. When purchasing new corms, buy plants from a reputable nursery and inspect them before planting. Varieties of gladiolus vary greatly in their susceptibility to Fusarium wilt. Whenever possible select disease resistant varieties.

Although the fungus is often first brought into the garden on infected corms, once introduced it can survive for years in the soil. Avoid planting gladiolus in garden areas that have had previous problems with Fusarium wilt. Soil that is neutral to slightly acidic (pH 6.6-7.0) will favor the plant over the pathogen and can help to reduce incidence of Fusarium wilt. A soil test (link to http://soiltest.cfans.umn.edu/) can be used to determine the pH of your soil. In addition, wounding of corms has been shown to increase disease problems so take care not to scratch or injure corms when planting.

Photos by Michelle Grabowski

Cherry Prinsepia

Kathy Zuzek, University of Minnesota Extension Educator



Princepia Kathy ZuzekCherry prinsepia (Prinsepia sinensis) is a little known shrub native to Manchuria that has been in cultivation since 1896.  It is a member of the enormous Rosaceae family, and close relatives of prinsepia that  you may be familiar with are woody ornamental and fruit varieties from the genus Prunus (cherries, peaches, plums, apricots, almonds) and pearlbush (Exochorda serratifolia).


Cherry prinsepia is one of the first shrubs to leaf out in spring, providing some welcome color after a long Minnesota winter.  Bright green leaves are alternate on current season's growth but are produced in clusters on older wood.  A thorn is found at the base of each leaf or cluster of leaves.  The small immature leaves are soon masked by an explosion of light yellow 5-petaled flowers on old wood in late April.  In Minnesota, cherry prinsepia blooms at the same time as flowering almonds (Prunus triloba var. simplex).   




Princepia flowers Kathy ZuzekAfter flowers fade, the abundance of bright green leaves produced on the cascading branches give the plant an appearance of what can only be described as a green haystack.  By late July, ½" red cherry-like fruit are found singly or in clusters on the plant.  Each drupe contains a single seed.  The fruit is edible but be warned that it is full of ascorbic acid!  Ascorbic acid does not seem to bother birds who love the fruit.  The fruit provide winter interest . . . if the birds don't find it first. 



Princepia fruit Kathy ZuzekPrinsepia's gray brown stems have chambered pith just as our native walnut and butternut trees do.  Stems cascade down providing a weeping plant habit to cherry prinsepia.  Growth on current years stems changes direction at each leaf node, giving each stem a zigzag look.  These weeping zigzag branches provide lots of textural interest.  Bark on older stems is brown and exfoliating, providing more textural effect.


Plants of cherry prinsepia on the University of Minnesota 
Princepia thornsSt. Paul campus and at the Minnesota Landscape Arboretum are 6-8' tall and wide.   Prinsepia is not a common shrub but is worth considering for hedges, screens, or as a specimen plant in the back of a garden.  It is used in shelterbelt plantings on the Canadian prairies.  Kansas State University, North Dakota State University, and the University of Nebraska all include Prinsepia sinensis on xeriscape plant lists.  Prinsepia has no major pests and prefers a sunny site on fertile, well-drained soils.


Photos by Kathy Zuzek


Bird Mites

Jeffrey Hahn, Asst. Extension Entomologist



northern fowl mites. Jeff HahnBird mites, especially the northern fowl mite, Ornithonyssus sylviarum, have been a common problem this summer entering homes and biting people. Bird mites are a major pest of chickens but will also parasitize many wild birds, such as pigeons, sparrows, starlings, and robins and are associated with nests that are built on or in homes and other buildings. Bird mites normally remain on birds and in nests throughout their lives where populations can grow to the tens of thousands.


If the mite populations become too large, or if the birds abandon their nest or die, the mites will move off en masse and look for an alternate food source and commonly enter homes. Bird mites are flat and the size of a pin-head, about 1/32 inch long. Although, they are very small, people can just barely see these mites. It also helps to see them when there are a lot of them around and they are moving.



When northern fowl mites encounter people they will taste test us, although they do not survive on human blood.  Their bites are annoying but fortunately bird mites do not transmit any diseases to people.  They also do not infest people and you will not accidently transport them and allow them to infest other buildings, like bed bugs.  Northen fowl mites do not survive off their hosts for more than a few weeks.


If you have a bird mite problem, it is important to find the bird nest that is the source of the infestation.  If the nest is empty, remove it, place it in a garbage bag, and throw it away.  If the nest is occupied by pigeons, starlings, or house sparrows, i.e. birds that are not federally protected, you can remove their nests even though there are birds still in it.  However, if eggs or young are found in nests of any song birds, they are federally protected and can not be disturbed as long as the nest is occupied.    Once the nesting season is over and only adults remain, you may remove the nest, as long you do not harm the birds.                         


You can use an insecticide application to help reduce the number of bird mites migrating indoors.  Pyrethroids, such as permethrin, bifenthrin, cyluthrin, deltamethrin are effective.  Treat outside around windows, doors, and other possible points of entry. If you can not treat an outside area without harming an occupied nest, do not spray. Leave the nest alone until it is abandoned; then you can spray the house if mites are still a problem. 


Once bird mites are inside your home, remove them with a vacuum or wipe them up with a cloth and rubbing alcohol.  Bird mites are also susceptible to dry conditions.  Running your air conditioner or a fan can help reduce humidity and kill bird mites.  Bird mites should go away on their own within several weeks.


Saturday, August 1, 2009

A Huge Thank You for Responding to the Yard & Garden News Survey!!



 




survey image Greetings Yard and Garden News readers!



First, thank you for your thoughtful responses on Y&G News' first ever reader survey. We were pleased to get so much positive feedback, and we have spent a lot of time discussing your comments about ways to make Y&G News even better.


The survey told us loud and clear that you value the timeliness and trustworthiness of the information, as well as the fact that it is Minnesota-specific. These things are important to us, too.


The survey also told us that many of you would like a shorter newsletter with postings more often, and that you would like a way to interact with the information and the educators.


In response to this, we have made the move from the one-way communication of our old webpage to the interactive options made possible with a blog. We want to stress that this new format still has the same quality information you've come to depend on. But now you can comment on the articles and take advantage of the RSS feed. It will also allow us to post more frequently.


We encourage you to explore these new features, or you can sit back, relax and read Yard and Garden News like you always have: This transition does not require any specific action from you. You will continue to receive emails from us, on the same schedule you're used to. You can easily see the lead in for the various articles and click to continue reading those you would like to. You can still click on photographs to view larger images. Photo captions can be viewed by placing your curser over the image.


Thank you,
David C. Zlesak and the Yard & Garden News team


 


 


 


 


 



What's Up With That?!





AARS entry 09R408This is sure a unique rose with its purple-red petal bases!! It is the new All-America Rose Selection (AARS) floribunda entry coded 09R408. Why haven't we seen this dramatic petal trait before in the roses at the local garden center? The answer is that this trait has been very difficult to bring it into modern rose cultivars and is coming from a source other than rose. One of rose's closest relatives, Hulthemia persica, is the source. Over the past 30+ years dedicated breeders have painstakingly made crosses between this wild rose relative and rose and then have made repeated backcrosses to rose.  The backcrosses to rose have been to gain more rose characteristics while still trying to retain the attractive red petal bases. Hulthemia persica is native to the region once part of the old Persian empire. It is typically found growing in very dry areas and has been difficult to cultivate in typical garden settings due to relatively high humidity and soil moisture compared to where it is native. It is different than rose (Rosa) in that it 1). does not have the two pointed paired stipules at the base of the leaf where the leaf attaches to the stem, 2). has only a simple leaf with one leaf blade rather than a compound leaf with multiple leaflets, and 3). it has a deep red blotch at the petal base. Hulthemia persica typically has rich yellow petals with deep red blotches.



Plants of H. persica tend to be more spreading and raspberry-like in growth habit than rose. Early Hulthemia / Rose hybrids have been available at a few specialty nurseries and have tended to have an awkward growth habit, be susceptible to mildew and black spot, bloom for a limited time, and be difficult to grow in the garden. Breeders are now making great strides in developing compact, floriferous hybrids that possess this highly sought after blotch and the more favorable garden characteristics of rose. Perhaps 09R408 will be the first such hybrid to win the coveted AARS award (aiming to be a 2013 winner). You can see this trial rose in the AARS trial beds in Minnesota at both Lyndale Park Rose Garden in Minneapolis and the Virginia Clemons Rose Garden in St. Cloud.   David C. Zlesak


Exploring the Potential for Large Leaved Rhododendrons for Minnesota

Laci High, University of Minnesota Graduate Student
PJM Rhododendron is well-adapted in Minnesota. David Zlesak



After a long, dreary Minnesotan winter, gardeners anticipate and appreciate the beauty of spring flowering shrubs such as rhododendrons and azaleas (genus Rhododendron) which can be the first sign of color in many landscapes.Due to its great soil adaptability and ease of cultivation compared to other members of the genus, PJM hybrids can be found along most residential streets in Minnesota.  These plants are loaded with lavender-pink flowers nestled among inconspicuous, scaly leaves.  Even though PJM hybrids have proven to be reliable performers for home gardeners, they lack the color range and glamorous trusses of broad-leafed forms typically found in more moderate climates.


Although distinctions between subgroups based on most observable traits hold many exceptions, the main difference between azaleas and rhododendrons is that azaleas generally have five stamens while rhododendrons develop ten. The subgroup rhododendron is further classified into lepidote (with scales on leaf surface) or elepidote (without scales); the latter often possesses larger leaves and flower trusses than the former as well.


Elepidote rhododendron 'St. Michel'. Laci High

Several deciduous azaleas and lepidote rhododendrons are well-suited for northern climates, but very few elepidote rhododendrons thrive in our region.  For those who have hiked the Appalachian Trail in the eastern U.S. or visited the Pacific Northwest in the springtime, you have likely encountered hillsides cloaked with elegant specimens of these broad-leafed rhododendrons.  The large, evergreen leaves may be valued by some avid gardeners, but these plants are mostly identifiable by their immense, terminal flower trusses and a felt-like covering on leaf surfaces termed indumentum.

The use of these elepidotes in Minnesota is primarily limited by their cold hardiness.  Traditionally, 'ironclad' cultivars such as 'Roseum Elegans', 'Nova Zembla', and 'Catawbiense Album' have continually survived our harsh winters.  The name 'ironclad' was given to these cultivars derived from the North American species R. catawbiense and have been shown to survive -25°F.  Although these plants possess satisfactory cold hardiness, their leggy habit leaves much to be desired in formal landscape plantings. 
In the 1970s, plant breeders at the University of Helsinki in Finland sought to develop extremely cold-hardy rhododendrons suitable for the Scandinavian climate.  They chose R. brachycarpum ssp. tigerstedtii, native to the Kongo-San mountain range in North Korea, as the primary seed parent.  This subspecies has been cited as the most cold-hardy rhododendron in existence (Tigerstedt and Uosukainen, 1996).  Crosses with 23 species and 48 hybrids yielded approximately 22,000 seedlings that were subjected to cold hardiness trials and evaluated for other valuable traits.  Finland experienced two bottleneck winters in the 1980s in which temperatures plummeted to -37°F and resulted in 70% of seedlings dying (Tigerstedt and Uosukainen, 1996).  However, adequate variation existed within this extensive population such that surviving genotypes were key candidates for further selection. Seventeen Finnish cultivars have been introduced and collectively are considered the most cold-hardy, broad-leaved rhododendrons available. 

It didn't take long for these hybrids to enter the North American distribution chain and are currently sold by many nurseries and garden centers in the northern states.  Growers and landscapers not only value cold-hardiness, but the Finnish hybrid collection offers a wide range of flower colors, glossy foliage, and several such as 'Haaga' have a compact habit.  However, when grown at latitudes south of Finland, such as those in Minnesota, vegetative growth below the terminal flower bud often occurs simultaneously with flowering such that the floral display becomes obscured; this vegetative bypassing effectively reduces the plant's ornamental value.  A few of the more popular Finnish hybrids can be found in local nurseries and several are on display at the Minnesota Landscape Arboretum's Rhododendron Display Garden.  For those of you anxious to establish broad-leafed rhododendrons in your garden that will succeed in our harsh climate regardless if flowers may become hidden, I recommend giving these a try (Table 1).

Table 1.  Finnish elepidote rhododendrons frequently found in the U.S. market.  Cultivar information provided by Kristian Theqvist, an amateur rhododendron breeder who has continued to build on the initial work performed at the University of Helsinki.


Cold Hardiness
Flower Color
Habit (height in 10 years)
Comments
'Haaga'
-33°F
Magenta pink with dark red spots
Compact (4-5 ft.)
Reliable bloomer
'Hellikki'
-29°F
Purple-red
Upright (4 ft.)
Prefers full shade
'Helsinki University'
-38°F
Light pink with dark red spots
Upright (5 ft.)
Reliable bloomer
'Mikkeli'

('St. Michel')
-35°F
Very light pink with green spots
Upright (6 ft.)
New growth covered with white wooly indumentum
'P.M.A. Tigerstedt' ('Peter Tigerstedt')
-33°F
White with dark red spots
Upright and spreading (4-5 ft.)
Slightly gangly in full shade

Bypass shoot development has been previously noted in R. brachycarpum ssp. tigerstedtii-derived cultivars grown in North America (Cox and Cox, 1997), and this adverse condition is worse at latitudes south of Finland.  This occurrence is likely due to differences in environmental factors such as photoperiod and temperature between Finland and Minnesota.  Variable responses to factors influencing flowering and dormancy in evergreen azaleas have been noted previously between American and European cultivars (Ballantyne, 1960; Jorgensen, 1970; Criley, 1985).  Since many other species and related cultivars don't exhibit a latitudinal gradient with respect to simultaneous vegetative growth and flowering, genetic variation must also exist in response to these factors.

Our research will manipulate photoperiod, temperature, and length of cooling period and then analyze how these factors affect timing of reproductive and vegetative budbreak as well as occurrence of bypassing.  Not only will this work aid our rhododendron breeding program, but conclusions may also facilitate research with other crops pertaining to apical dominance (inhibition of lateral bud growth by the terminal bud of a shoot).

The ultimate aim of our research will be to introduce extremely cold-hardy, broad-leafed rhododendrons that break vegetative growth only after the floral display is complete.  Starting our breeding efforts with select Finnish cultivars that already possess many redeeming qualities, we will perform crosses with 'ironclad' cultivars that typically do not show vegetative bypassing.  We anticipate that our breeding efforts will lead to several new hybrids that will not only thrive in cold, temperate climates, but also increase the diversity of broad-leafed rhododendrons on the market.  Minnesotan gardeners will then be able to enjoy the beauty of these ornamental shrubs that have previously been hallmarks in only the most moderate climates.

References

Ballantyne, D.J.  1960.  Growth regulators and the flowering of evergreen azaleas (Rhododendron cv.). (Doctoral dissertation, University of Maryland, College Park).

Cox, P.A. and K.N.E. Cox.  1997. The encyclopedia of Rhododendron species. Glendoick Publishing, Perth.

Criley, R.A. 1985.  Rhododendrons and azaleas, p. 180-197.  In:  A.H. Halevy, (ed.).  CRC handbook of flowering, (v. 4).  CRC Press, Boca Raton, Florida.

Jorgensen, S.  1970.  Azalea production.  Pennsylvania flower grower's bulletin, 232:  5-7.

Tigerstedt, P., and M. Uosukainen.  1996.  Breeding cold-hardy rhododendrons. American Rhododendron Society 50 (4):  185-189.

Helping Lawns Cope with Summer Stresses

Bob Mugaas, University of Minnesota Extension Educator




Irrigation can help reduce drought stress. David Zlesak.
Each summer, temporary periods of hot, dry conditions commonly occur in this part of the country.    Each summer these conditions prompt many questions about caring for and watering our lawns (as well as other landscape plants).   Following are some lawn care tips to help cope with these dry conditions during Minnesota summers.

1.  Where lawns are maintained in an actively growing condition, keep mower heights of cut between  2.5 to 3.0 inches  to encourage deeper rooting.  The cool season lawn grasses common to this area have naturally shallower, less robust root systems during the middle of the summer compared to the spring and fall periods of the year.  Shorter mowing heights without an accompanying increase in water can make that situation even worse and unnecessarily stress the plants.


2.  Avoid the use of postemergence broadleaf or crabgrass killers during hot dry conditions or any time the lawn is under drought stress, even during cooler periods.  The term postemergence means the weedy plants are up and readily visible.  Most of the products used during the growing season, with the exception of preemergence crabgrass weed killers, are applied as postemergence products to the actively growing weeds.  The operative word here is 'actively' growing weeds.  The same summer stresses that impact our grass plants can also slow the growth of many perennial broadleaf weeds.  Thus, they may not be as sensitive to an herbicide application under these conditions compared to one applied in September to early October when they are again more actively growing.


3.  During the summer months of July and August, actively growing lawns in a well watered soil utilize about 1 to 1.5 inches of water per week in the Twin Cities area.  Historically, that has been the amount of water we have tried to replenish to our lawns on a weekly basis.  However, the practice of "deficit irrigation" has become more and more common place over the last several
years.  In this practice, water is replenished at less than the amount of actual water lost during any particular growing period.  Research has shown that under average summer conditions, lawn grasses will maintain acceptable quality even if less than the total water lost from the lawn isn't replenished.  For example, applying an inch of water every two to three weeks instead of once per week could save a third to a half of the water used during the summer months while maintaining an acceptable lawn.  Shorter intervals are needed during very hot, dry conditions while more moderate temperatures allow for a little longer interval between watering.  While there may be some browning of the grass during these stress periods, most plants will remain alive and begin to grow again once more favorable conditions return.   

4.  Where soils are more clay like and/or compacted or soils are sandy, consider splitting the applications in half and apply more frequently.   Since root systems will be somewhat shorter during this period, applying  a little less water per time but a little more frequently will help ensure that water will not pond or runoff of the surface in the case of heavy clay and/or compacted soils.  Likewise, in a sandy soil, it will help ensure that excess water does not drain past the grass plant's rootzone and hence be wasted. 


Thumbnail image for Common drought stress symptoms on Kentucky bluegrass lawn. Bob Mugaas.5.  It is generally best to allow the grass to grow more slowly during the summer stress periods rather than trying to force excessive grass blade growth by applying high rates of nitrogen fertilizer.  The stimulus provided by the nitrogen fertilizer will result in increased water demand by the plant, more frequent mowing and usually a more rapid depletion of plant nutrition and energy reserves.  All of those can make the plant more vulnerable to summer stresses, particularly heat and drought stress.   For most average lawns, holding off applying fertilizer for a few more weeks, until around Labor Day, is more beneficial for the grass plant than applying during the summer stress periods.

6.  There are instances where the heat and dryness of summer are just too much for our grass plants and some permanent injury can occur.  This most commonly occurs where there is no possibility for supplemental water to be applied in amounts to at least keep the plants alive.   On the brighter side, where loss of turfgrass has occurred, the period from mid-August through about the middle of September is an ideal time to do some overseeding and repairing of those areas damaged or destroyed by stressful summer conditions.  Seeding at this time of year avoids significant competition from annual weeds and takes advantage of the natural cooling of temperatures.  This also coincides with a time of year when rainfall is more frequent although supplemental irrigation can certainly be used to provide a uniform grass seed germination and early growth environment. This greatly improves the chances for successful establishment.  In addition, this might be just the situation needed to allow for the introduction of more drought tolerant grasses such as the fine fescues into our lawns.  While seeding is certainly one option for repair, resodding can be a quick and convenient way to repair an area.  Making sure that the sod remains moist but not soggy for at least the first couple of weeks after installation will be necessary for successful establishment of the new sod.   Never allow new sod or young grass seedlings to completely dry out as that will usually result in their death.

Looking for Bacterial Leaf Scorch in Minnesota

Michelle Grabowski, University of Minnesota Extension Educator



Bacterial Leaf Scorch (BLS) is a disease of shade trees common in the southern states and known to occur as far north as Ontario and as far west as Texas. To date, however, it is unclear if this disease occurs in Minnesota and how common it might be. It may seem unusual that a disease of a large tree might go unnoticed for years, but many states, having never reported Bacterial Leaf Scorch previously, have found multiple infected trees once scientists began looking for the tiny bacterial pathogen. Recent reports show that BLS is becoming more common in northern states like New Jersey. Scientists now want to know, does BLS occur in the upper Midwest?



The reason that BLS can slip by unnoticed is that the symptoms it causes look very similar to the symptoms caused by several other diseases and by environmental stress. Scorch is the term used to describe leaves that have singed brown edges. In shade trees infected with BLS, the margins and tips of the leaves turn brown. Unfortunately leaf browning at the edges and tip of the leaf is also commonly seen in trees stressed from drought, compacted soil, restricted root growth, salt damage and many other factors. In addition, diseases like oak wilt and Dutch elm disease can cause browning of leaves that may be confused with BLS. In the end, scientists rely on several laboratory tests, like ELISA, PCR and electron microscopy, to determine if BLS is truly present or not.






Bacterial Leaf Scorch is caused by a tiny bacterium called Xylella fastidiosa. Infection can occur in a wide variety of shade trees including oak, elm, linden, mulberry, maple and many others. These bacteria live in the xylem, or water conducting cells of the infected shade tree. Leaf scorch is the result of the bacteria blocking the flow of water to the leaves and may also be caused by a toxin produced by the pathogen. In BLS infected trees, scorched leaves typically first appear in mid to late summer; August and September in Minnesota. Newly infected trees may have only a few branches with scorched leaves scattered throughout the canopy. As the infection continues year after year, more of the tree's canopy becomes affected. Eventually, the tree's growth slows, branches die and the entire tree may be killed. BLS is spread from tree to tree by leafhoppers and spittle bugs that pick up the bacteria while feeding on infected trees. The BLS bacteria can only survive inside an infected tree or within an insect vector. To learn more about the life cycle, biology and management of BLS visit the American Phytopathological Society education center .


 




Surveys are being conducted this summer to determine if bacterial leaf scorch is present in Minnesota's shade tree population. If you have a shade tree with leaf scorch symptoms and would like to contribute a sample to the survey please contact Michelle Grabowski, extension educator with the University of Minnesota at 763-767-3876 or magrabow@umn.edu. There is no charge to send a sample. One pencil width branch with 3-5 leaves attached is all that is needed to test a tree for BLS. Trees of interest include oak, elm, sycamore, maple, mulberry, ash, linden, horse chestnut and other shade trees.



Photo credits

Photo 1. B.Olson OK State University, NPDN   


Photo 2. A.B. Gould, APS Education Center 




One Cool, Interesting Insect

Jeffrey Hahn, Asst. Extension Entomologist



Mantidfly. Jeff HahnSeveral people reported recently finding a small, ½ inch long, insect that resembles a preying mantid and a paper wasp. This unusual looking insect is known as a mantidfly. It looks like a preying mantid because of its large, front legs which are modified for grabbing prey. Mantidflies are commonly reddish brown with yellow with wings that are half brown along the front margin half and clear. Although they may not be frequently seen, mantidflies are reasonably common in Minnesota.


Mantidflies commonly parasitize spiders while other species lay eggs in the soil where the larvae prey on scarab beetle grubs, noctuid moth larvae, or social wasps. Adults feed on small insects they capture. Mantidflies are common on foliage in wooded areas during summer. People have generally found these insects outdoors but in at least one case a mantidfly was found that had accidently entered a house. Fortunately, these insects are harmless to people. If you should find one in your home, just release it outdoors.



Be On the Watch for This Elm Insect

Jeffrey Hahn, Asst. Extension Entomologist

Elm flea weevil. Jeff Hahn.
The European elm flea weevil (EEFW), Orchestes alni and it's damage, was found on the University of Minnesota St. Paul campus during July.  It was found by Dr. Curtis Young, an extension entomologist at Ohio State University.  This invasive insect, common throughout Europe, was first found in the U.S. in 1982.  It wasn't found in the Midwest until 2003. It was first found in Minnesota in 2007 when an adult was collected on the St. Paul campus.

The adult EEFW is small, 1/10 - 1/8 inch long.  It is reddish brown with black spots or dark brown to black, with a long, conspicuous snout and large back legs which allows it to jump.  This weevil feeds on Siberian elm, Chinese elm, and hybrids with Asian parentage.  It rarely feeds on American elm.

EEFW overwinters as an adult and becomes active in the spring.  It moves to elm and feeds on the underside, windowpaning small areas, i.e. feeding on the lower surface of leaves but not chewing through.  A thin, opaque layer of leaf tissue remains.  Eventually, this chewed area dries up and fall out.  Don't confuse this injury with elm leaf beetle feeding which chews small oval holes in the leaves with the edge of the holes remaining green.

Soon after they emerge and feed, adults lay eggs along the edges of the veins.  When the larvae hatch, they feed as leafminers inside the leaves.  They move to the tip of the leaves where they create blotch mines.  The larvae feed for a few weeks and then pupate.  Adults emerge later in the summer and feed until fall.

Elm flea weevil feeding. Jeff Hahn.The feeding damage by EEFW is primarily cosmetic, only affecting the appearance of the tree.  It is very unlikely that elm are injured as a result of EEFW feeding making treatment unnecessary.  It is possible that if trees were severely defoliated, particularly if they are recent transplants or already stressed, they could further weakened elm and make them more susceptible to other problems.  If treatment is desired, an application of imidacloprid in early spring should be sufficient to manage this weevil.

We are interested in sightings of this insect and/or its damage in other areas of Minnesota.  If you believe you have EEFW, please contact Jeff Hahn (hahnx002@umn.edu ).

Garden Calendar for August


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


Although most of Minnesota has received some rain recently, we are still well below average for the year.  Continue to water plants as needed.  Containerized plants and recently transplanted trees, shrubs, and herbaceous perennials have limited root volumes from which to draw mo
isture and needed to be checked frequently for their need of supplemental water.  For most situations it is best to water deeply and thoroughly less often than providing frequent shallow water applications that don't penetrate the root zone.

    








Thumbnail image for Early August is a good time of year to divide bearded iris. David ZlesakAs we enjoy all the bounty of the summer season in our gardens, keep an eye out for pests.  Frequently scouting the garden for pests when we are out enjoying our plants anyways can help us become aware of a problem before it goes out of hand and we can realistically have a chance to effectively intervene.  Pests can include insects, microorganisms (fungi and bacteria), and other wildlife such as rabbits or deer.

Early August is a great time of year to divide and replant bearded Iris and also purchase new plants.  The leaves can be cut back in order to make them look more attractive and reduce some of the water demands and stress on the recent division.  Plants will put out additional roots before winter sets in.  Keep the iris rhizome (swollen stem part that serves as a storage organ for the plant and grows parallel with the surface of the soil) at the soil surface and slightly exposed.  For more on iris, please visit www.extension.umn.edu/distribution/horticulture/M1267.html


Careful pruning and traininig of tomatoes helps with light penetration to fruit and ripening. David ZlesakFor indeterminate tomatoes, continue to train the plants and prune out unnecessary side branches to allow more light and energy to be devoted to the maturing the developing fruit.  With the cool summer, tomatoes are developing and ripening slower than in recent years.

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