Yard & Garden Line News September 15, 2002

Yard & Garden Line News
Volume 4 Number 15 September 15, 2002

Features this issue:
Getting Roses Ready for a Minnesota Winter
Hardy Fall-Blooming Perennials
Foreign Grain Beetles Common This Summer
Black-eyed Susans get KO'd
Editorial Notes

Getting Roses Ready for a Minnesota Winter
David C. Zlesak
Marketing and Production

'L. D.
Braithwaite', a David Austin rose. Photo credit: Beth Jarvis

Roses have developed a bad reputation, in part, due to difficulty overwintering many of them. Thankfully, many truly winter hardy roses, adapted to Minnesota, have become increasingly available in recent years.

In the past, upper Midwest rose growers were almost ignored by rose mass marketers because we are a relatively small share of their market. Large wholesale growers in Arizona, California, Oregon, and Texas grow mostly modern winter-tender hybrid teas, grandifloras, and floribundas and sell the same cultivars to retail garden centers and mail order firms from Florida to Minnesota. They typically sell bud-grafted roses and use an old climbing rose called 'Dr. Huey' as their rootstock. 'Dr. Huey' is easy to propagate, vigorous, and easy to graft. Unfortunately, this rootstock is relatively cold sensitive which complicates overwintering many of the modern roses grafted onto it.

Due to the increasing demand for low-maintenance roses for northern landscapes, some national growers are increasing production of more winter hardy cultivars to meet our needs. In addition, many northern rose nurseries have started and specialize in a large selection of winter hardy rose cultivars.

Most specialty nurseries and some large scale national growers are exploring what is termed own-root production. By rooting cuttings of cultivars, instead of grafting, the roots and the shoots are genetically the same (the rose is on its own roots) and winter survival can be enhanced. When plants suffer severe dieback, any emerging shoots from the own-root plant will still be the desired cultivar. With grafted roses, if dieback occurs beyond a graft, the desired cultivar is lost and emerging shoots will be from the rootstock. Currently, most rugosa and shrub rose cultivars are sold as own-root plants in the Twin Cities area. In addition, some specialty nurseries offer grafted plants of hybrid teas and other typically tender roses on rootstocks with greater winter hardiness such as Rosa canina, R. eglanteria, and R. multiflora.

Minnesota-Hardy Roses

'Carefree Beauty', a Buck rose. Photo credit: Beth Jarvis

Many of the Minnesota-hardy roses being advertised are not recent releases but have actually been around for over a century. Some examples include the popular rugosa hybrids 'Blanc Double de Coubert' (1892) and 'Belle Poitevine' (1894).

Recent hardy introductions from the past thirty years predominate and have been developed by breeders primarily from Canada (Explorer and Morden/Parkland rose series), Germany (Pavement series), and the United States (Dr. Griffith Buck roses).

There are many wonderful rose cultivars that can be easily overwintered in Minnesota, but identifying them can sometimes be a challenge due to overoptimistic marketing by especially national nurseries trying to reach the Northern market.

If you are interested in growing roses that don't need any or much winter protection, take advantage of local resources! You can ask Master Gardeners, Consulting Rosarians from the American Rose Society, and reputable nurseries what roses perform well in our climate. In addition, see for yourself what is doing well at public gardens where supplemental winter protection is not provided such as the shrub rose garden at the Minnesota Landscape Arboretum. Attached is a table listing cultivars and their cane survival at the Minnesota Landscape Arboretum shrub rose garden and the Bailey Nurseries display garden.

How a Plant Tolerates Cold

'Bonica'--mulched
with snow and 'Bonica' in spring --dead to snowline. Photo credit: David Zlesak

When water freezes on our window panes we often see interesting patterns as jagged ice crystals branch and grow in size. If ice crystals are allowed to form in plant cells, they can rupture cell walls and organelles beyond repair. This is the cause of most of the dieback we see in spring on the tips of stems that were actively growing and were especially high in water content entering winter. Hardy plants combat cell damage from ice crystals by increasing their sugar and soluble salt concentrations and by taking advantage of a process called supercooling.

When sugar and soluble salts are dissolved in water, it will not freeze at 32 degrees Fahrenheit, but at a lower temperature (this is why we put salt on our sidewalks). These solutes, at most, can prevent cellular water from freezing at about the mid 20's F. Potassium is one element that is especially useful to plants in this process and is designated by the third number on fertilizer formulations.

Below the mid 20'sF, supercooling is the next survival mechanism hardy roses use. Supercooling is when cellular water is removed from within the cell and pushed out between the cells where it is allowed to freeze safely. The better a plant is at doing this, the lower the temperature it can tolerate before dying. Water in very thin films resists freezing, so the goal of supercooling is to have just thin films of water around organelles in cells with the rest of the water pushed between cells.

In addition to providing some insulation for the more tender roses we have chosen to grow, our goal as rose growers is to provide conditions that encourage plants to go into natural dormancy in the fall so they can best manage their soluble salts and be efficient in supercooling.

Cultural practices to stimulate dormancy and enhance winter survival

Planting depth
-Plant the crown (where stems and roots join) of own-root plants and the bud union of grafted plants a few inches below the soil line. This allows for more buds of the cultivar to be available to sprout from if killed to the soil line or girdled by rodents.

Discourage succulent late-season growth by:
-Ending nitrogen fertilization in late-July.
-Not pruning heavily in late summer or fall.
-Discontinuing to deadhead spent blooms in September.
Encourage sugars to accumulate and healthy soluble salt levels by:
-Maintaining good watering practices throughout the fall.
-Preventing diseases and severe insect damage.

What to Do with Your Roses Before Winter

The goal of winter protection isn't to keep the frost out, but to keep it in and to prevent freezing and thawing. Materials that insulate and prevent extreme temperature variation such as mulch, soil, canvas, and Styrofoam have been widely used on roses and tender perennials. There are benefits and drawbacks to the use of these insulators and each gardener must decide for themselves which options best fit their objectives and budget.

No matter what insulator is used, there are some general characteristics that the better insulators share and include: free of weed seeds (hay often contains weed seeds) and free of chemicals that will hinder rose growth (herbicide treated lawn clippings, wood chips from a black walnut or freshly cut white pine). In addition, a superior insulator should not mat down from moisture and encourage molds and diseases to develop from lack of air circulation. (Maple leaves are often avoided for this reason) Styrofoam cones, or rose cones, are widely available come fall, but in our climate typically do more harm than good. Heat and moisture can build up in them on a sunny winter day and bring the roses out of dormancy so night time's plummeting tempoeratures lead to ice crystals and cell death.

Extremely Hardy Roses

Some roses, such as many of the pure rugosa hybrids, are hardy enough to withstand Minnesota winters on their own with little or no cane injury. It is often best to just leave them alone and treat them like any low-maintenance landscape shrub. By insulating them with mulch or enclosures there may not be any benefit from the labor and plants can be damaged from unnecessary handling.

Crown Hardy Roses

Many roses sold as hardy in Minnesota are actually crown hardy, the plants typically die back to the snow or soil line and regrow and bloom vigorously from new canes initiated from the base of the plant. These roses include most of the Dr. Griffith Buck and Morden roses as well as some Explorer roses. Crown hardy roses can benefit from insulation around the base of the plant to prevent excessive cane dieback.

One of the easiest thing to do with such roses is to add an extra 4-12" of mulch around their base after the ground is frozen and pull it back in the spring before new growth is too far along that it gets damaged from handling. Mulch can be safely placed before the ground is frozen if it is not high in nitrogen, which could cause it to heat and compost. If you use bark or wood chip mulches or leaves to dress your beds, get a fresh supply in the fall to use as insulation of canes and then spread and redress the beds each spring.

Soil is also a great insulator that can be mounded around plants, but can be laborious to carry and remove. If you have rock mulch or choose not to dress beds with the insulation material, insulation material can be enclosed in netting or even garbage bags that can more easily be removed come spring.

Tender Roses

Not tipped, just buried in soil and mulched.

Bags and soil are removed in spring.
Photos: Beth Jarvis

There are roses such as many hybrid teas, grandifloras, and floribundas (most roses sold in Minnesota) that are not reliably crown hardy here and depend on insulation for consistent survival. Such roses can be treated like the crown hardy roses with insulators mounded up over their bases and removed in the spring. With such roses, pile the insulators up a little higher (foot or more) because you can expect cane dieback well into the insulation material. To aid in positioning larger amounts of insulation, create enclosures. Enclosures can easily be make out of wire or other materials and placed around individual roses or an entire bed. The insulation can then be secured within the enclosure and prevented from blowing away.

In addition to mounding insulation around tender roses, there are other techniques such as the Minnesota tip method and complete removal and burying. This is best done after a couple hard freezes to cease growth and before soil is frozen and difficult to dig.

The Minnesota tip method involves loosening soil on one side of the plant to free the root system and digging a hole on the other side of the rose a few inches deep. Leaves are stripped off the rose and a fungicide spray is typically used over the canes before burial. Canes of the plant can be tied together to condense them and they can be cut back to a couple feet or so. The plant is then pushed over into the hole, mounded over with soil, and then mulched after the soil is frozen. Wise tippers also mark the base of the plant and top of the canes with stakes for easier resurrection come spring. The Minnesota tip method is a useful technique to protect greater cane length of tender roses.

In addition, whole plants can be uprooted and buried in a common grave and be replanted come spring. Plants are typically prepared like the Minnesota tip method- foliage is removed and canes are tied to condense branches.

In general I have been satisfied with mounding the base of tender roses for winter survival. I lose more cane length than if I did the Minnesota tip method or common grave method, however, by not disturbing the root system the plants are less set back in spring and grow quickly. Often by July after a typical or mild winter, a rose given the Minnesota tip method and the mounding method are comparable in size. The Minnesota tip method and the common grave method require greater labor and can be more challenging to use, but if done well can aid in having larger plants come spring.

Once tipped and buried plants are resurrected and replanted, it is especially important to water plants well and closely monitor the canes so they don't dry out and become stressed because of a compromised root system. You can use materials such as moist burlap and antitranspirants to help shade and retain moisture in the canes during the recovery period.

Special Cases

Tree Roses
Tree roses need special protection in our climate. The decorative cultivar we enjoy is grafted to the top of the tree with the trunk being a different rose. It is therefore important to make sure not only the top, but also the whole trunk over winters well. The Minnesota tip method is the most common method used to protect tree roses in our climate.

Climbing Roses

Rodent-nibbled rose Photo credit: David Zlesak

Since many climbing roses and some antique and shrub roses bloom predominantly off of side branches from the previous year's canes, it is important to protect as much wood as possible of marginally hardy cultivars. The Minnesota tip method is one option. Another method is to create a very large enclosure, bend down the canes within the enclosure and accumulate large quantities of dry mulch around canes. At home we have successfully overwintered the climbing cultivar 'Alchymist' (15' tall) and the damask 'Mme. Hardy' this way.

In addition, since some of our crown hardy roses are planted nearby, they get placed within the large enclosure and protected as well. When using a larger volume of mulch, it is especially important to use insulators that will not get waterlogged and matte. Materials that I have successfully used include corn cobs, straw, loose oak leaves, and maple and elm leaves kept dry in garbage bags. In the use of mulch to directly insulate canes, it is beneficial to add rat poison so mice won't find a warm home and knaw rose bark off for food. On the first warm days of spring, begin to slowly remove mounded mulch so heat doesn't build up and mold develop.

Roses in Containers
Roses make great container plants, especially miniature roses. When winter comes many find it hard to resist taking containerized roses indoors and storing them in the basement or trying to keep them as a houseplant. Often people are disappointed with their performance indoors. Low light levels and pests such as spider mites make it a challenge to have these roses look as beautiful inside as they did outside. You can invest in supplemental light and have success, but many gardeners find it easier to just bury the whole pot and all in the garden and resurrect it come spring. Leaving relatively small containers unprotected outside during winter can kill even reliably hardy roses and other typically hardy plants. Roots are less cold hardy than stems and the soil in pots does not have the insulation factor provided by the earth and become the same temperature as the air.

What to do come spring

Many people are afraid that they may take off insulation material too early in the spring and when they do start to remove it are surprised to find long white and yellow shoots reaching for light. On sunny spring days temperatures can be higher in the insulation than what the air temperature is, especially in organic insulators where some composting may be occurring. During most years, you can begin to remove insulation by mid-April. By removing insulation relatively early in the spring before shoots have begun to sprout, you reduce the risk of shoot damage. There will not be long new shoots to accidentally break off as you physically remove the insulation and ambient temperatures will help acclimate the new shoots and allow them to grow at a slower and more reasonable rate in accordance with the weather. If an untimely hard freeze is predicted, you may choose to provide temporary insulation until the cold snap passes.

May we all successfully make it through another Minnesota winter, roses and people alike!

Editor's note: To see the most recent rose hardiness data, click here.

Yard and Garden Brief Hardy Roses
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h108roses-hardy.html

Yard & Garden Brief Minnesota Tip Method of Protecting Garden Roses
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h112rose-mntip.html

View on line copy of Roses For the North
http://www.extension.umn.edu/distribution/horticulture/DG6594.html

Hardy Fall-Blooming Perennials
Deborah Brown, Extension Horticulturist

'Moonbeam' coreopsis.

Fall-blooming aster

Goldenrod.

Helenium.

Stonecrop

'Rose Blush' Photos: Deb Brown

Autumn's arrival can be a bittersweet time for flower gardeners because it's a reminder that cold weather and dreary winter landscapes are just around the corner. But there's no need to give up on color in your garden just yet. In addition to bright flowering annuals, there are a number of hardy fall-blooming perennials that can extend your garden's beauty right until frost or a little beyond.

In southern Minnesota, there's still time to plant flowering perennials. The further north you live, the more dicey it gets once we pass mid-September. It's always best to plant when there's still three or four weeks of fairly mild weather. That gives the plants' roots time to start becoming established before the ground begins to freeze in earnest.

The first late-blooming perennial that comes to most gardeners' minds is chrysanthemum, which actually can tolerate light frosts and keep right on flowering. Though not always fully hardy in our area, mums usually come through winter in pretty good shape as long as they're mulched in late autumn soon after hard frost finally takes its toll and the soil begins to freeze.

(Mulching with about six inches of straw is always a good idea for overwintering perennials here. Not only does it protect them from extreme cold, it insulates their roots from fluctuating temperatures and keeps them from sprouting too early in spring, before weather conditions grow consistently mild enough to prevent injury.)

Plant breeders at the University of Minnesota have introduced a number of beautiful chrysanthemums that will bloom early enough in autumn to be useful here. Some others may be just as hardy, but often they're only beginning to set flower buds when hard frost in late October or early November takes them out.

Look for mums with the prefix "Minn" in their names; they're all cushion mums that make mounds of brightly colored flowers. Larger-flowered types developed at the U include "Rose Blush", "Lemonsota", "Grape Glow", "Centerpiece", and the "My Favorite Mum" series, along with many more.

Here's a quick run-down on some other late-blooming perennials to consider. While you can purchase pots of Minnesota mums and some other perennials now, most of the others will be available at garden centers or from specialty nurseries and mail-order catalogs next spring. Or, you may be able to start them yourself from seed.

* Hardy asters: Many species of perennial asters grow well here; those known as "Michaelmas daisies" have been hybridized to produce showier flowers than most, with colors ranging from pink, rose and cerise to lavender, lilac, purple and blue.

* Boltonia (Boltonia asteroides): These native plants look very much like asters, but are covered with 3/4 inch flowers on tall many-branched stems. Unlike some of its floppier relatives, the cultivar "Snowbank" grows to only four feet and needs no staking.

* Goldenrod (Solidago species) : People mistakenly associate the name "goldenrod" with hayfever because these native plants bloom the same time as our ragweeds, which are the true culprits. This is probably why they're more popular in European gardens than in North America where they originated. Compact cultivars include "Cloth of Gold", "Gold Dwarf", and "Golden Thumb", with stems 1 1/2 feet in height or less; "Crown of Rays" and "Peter Pan" are a bit taller.

* Helenium (Helenium autumnale): Helen's flower (sometimes called "sneezeweed") deserves to be grown more commonly in Minnesota gardens. These tough perennials bloom profusely with two inch daisy-like flowers, each with a prominent, raised center. Autumn colors abound; cultivars range from yellow, gold and orange to bronze and mahogany with dark centers.

* Kamchatka bugbane (Cimicifuga simplex): This is another fall-blooming perennial that deserves to be planted extensively. It has attractive, ferny foliage all summer, then develops white "bottle brush" flowers in autumn. The cultivar "White Pearl" has showy large clusters of flowers and grows three to four feet tall.

* Monkshood (Aconitum species): Please note, all parts of this perennial are toxic when eaten; plant it only if you're certain no young children will have access to it. On the plus side, it has tall stems of intriguing one inch helmet-shaped flowers in shades of pale blue to intense violet or bi-colors, depending on the cultivar you choose. And, it's about as winter-hardy as a plant can be.

* Obedient Plant (Physotegia virginiana): Another extremely hardy plant, this perennial gets its common name from the flowers' ability to remain facing whatever direction you position them. Three foot spikes of white, pink or rose-colored flowers develop in late summer or early autumn and are good as cutflowers, too.

* Stonecrop: This name refers to upright sedums that develop dense clusters of rose-beige or pink flowers very late in summer. It's fun to watch as the color appears, then slowly fades over several weeks. "Autumn Joy" is the most commonly available cultivar; "Meteor" and "Brilliant" are more vivid pink.

Finally, don't forget that some perennials begin blooming mid-summer, then carry on until frost. Two excellent examples are Russian sage (Perovskia atroplicifolia), with its spikes of lacy lavender blooms, and Threadleaf coreopsis (Coreopsis vertcillata), a plant that keeps pumping out incredible numbers of delicate yellow daisies all season long.

Each is a winner of the prestigious Perennial Plant Association's "Plant of the Year Award", indicating that they are recognized by professional growers and gardeners alike for their reliable performance in gardens across the country.

Foreign Grain Beetles Common This Summer
Jeff Hahn, Assistant Extension Entomologist

Foreign grain beetle Photo credit: Jeff Hahn

A lot of people have been finding very small insects in their homes that are described as being either fly-like or beetle-like. These insects are foreign grain beetles, Ahasverus advena. People typically find these insects around sources of moisture, such as sinks, basins, bathtubs. Foreign grain beetles are found in homes in August and September when humidity is generally high. With the high amount of rainfall we have experienced this year, these insects are particularly common now.

Foreign grain beetles are about 1/12 inch long and reddish brown. Under magnification, you can identify them by a pair of peg-like projections behind their head on the prothorax. Because of their small size, foreign grain beetles are sometimes confused with fruit flies or some other small-sized flies. While foreign grain beetles readily fly, they are hard-shelled while fruit flies are soft-bodied. They also fold their wings out of sight when they land which fruit flies can not do.

When foreign grain beetles are walking, especially if they inadvertently land on somebody, it is possible to confuse foreign grain beetles with fleas. However, foreign grain beetles are flattened from top to bottom while fleas are flattened from side to side. Also fleas do not fly, while foreign grain beetles can.

Foreign grain are scavengers, feeding on fungi and mold and organic material. Despite their name, homeowners rarely see foreign grain beetles attacking dry food products, such as flour or pasta, unless it is old and moldy.

In most cases when these beetles are present, they are associated with newly constructed buildings. Moisture from the green wood supports mold and fungus on wood and drywall. Foreign grain beetles feed on this, allowing their numbers to build up in wall voids. When numbers are large, they come out from behind the walls into the living areas of homes. Foreign grain beetles may also be found in older homes with high humidity and poor ventilation.

Foreign grain beetles are harmless; they do not bit people, damage wood or infest food (unless they find damp, moldy grain products). However, they can be a nuisance when large numbers are present. The best control is to physically remove the insects with a vacuum cleaner. In the short term, foreign grain beetles will be present until late September or early October and then go away on their own. When they are infesting new homes, they persist only for a few years until the wood dries and then they die.

Insecticides are not warranted because the problem is temporary and the insects do not cause any real harm. The effectiveness of an insecticide spray at best would be very short-lived and would not prevent more foreign grain beetles from appearing.

Black-eyed Susans get KO'd
Janna Beckerman, Extension Plant Pathologist

Rudbeckia blooms from July through frost.

Septoria leaf spot devastates Rudbeckia Photo credit: Janna Beckerman

Angular lesions may be Septoria. Microscopic ID is necessary.
Photo credit: Janna Beckerman

Cylindrosporium symptoms are milder than Septoria.
Photos:
Chad Behrendt.

Powdery mildew of Rudbeckia Photo credit: Chad Behrendt

Black-eyed Susans (Rudbeckia spp) are popular annuals and perennials. Their popularity is not without reason: A profusion of bright, yellow flowers (up to 5" in diameter) develop on bushy plants with dark green, lanceolate foliage. For this reason and many others, Rudbeckia fulgida var. sullivantii 'Goldsturm' was selected by the Perennial Plant Association as the 1999 Perennial Plant of the Year. 'Goldsturm' was significant in its compact habit, and 1-2" golden-yellow petals that encircle a black cone of disk flowers. Plants are literally covered with a "gold storm" of flowers from July through September. Rudbeckia can make a dramatic statement in the garden.

Plant pathogens can make dramatic statements, too . Very few of us actually enjoy these statements (especially when it is happening to us!). Unfortunately, as happened with Echinacea purpurea 'Magnus' (the 1998 Perennial Plant of the Year), wide-scale distribution of cultivar 'Goldsturm' resulted in the discovery of new disease problems. Most of these disease problems affect all members of the genus Rudbeckia, to varying degrees. Accurate diagnosis requires the use of microscope with exceptions for powdery mildew (which is clearly visible to the naked eye) and aster yellows (which requires laboratory diagnosis).

Septoria Leaf Spot of Rudbeckia
The fungus, Septoria rudbeckiae, is one of the most common foliar pathogens of Rudbeckia. Symptoms begin as small dark brown lesions that enlarge to 1/8 - 1/4 inch in diameter. Although the lesions are usually rounded, there may be angles where leaf veins limit the spread of the fungus. Symptoms of this disease may be difficult to distinguish from the angular leaf spot of Rudbeckia. Ultimately, these two diseases can be distinguished from one another by examination under a microscope.

Microscopic examination of the lesion will reveal black, flask-shaped structures called pycnidia that contain thousands of threadlike-spores. Spores are produced in late spring and early summer, causing leaf spots on the lower leaves, with the initial inoculum having overwintered on tissue infected the previous year. The spores of the fungus are dispersed by splashing water, with lesions first appearing on lower leaves and later developing on upper leaves as the season progresses.

To manage this disease, remove the infected leaves at the end of the growing to reduce inoculum levels. Because leaf moisture is essential for infection to occur, increase air circulation around the foliage by properly spacing plants (and removing volunteer seedlings) to prevent over-crowding. As with other foliar disease problems, avoid overhead watering. Fungicides containing chlorothalonil or copper* may protect new growth and reduce the spread of the disease. Preventative applications of fungicides should begin in early to mid June prior to the onset of symptoms.

Cylindrosporium and Ramularia Leaf Spot of Rudbeckia
Ramularia rudbeckiae and Cylindrocladium spp. have been reported as causing leaf spots on members of the genus Rudbeckia. Like Septoria leaf spot, frequent watering (due to rainfall or irrigation) that results in leaves that are wet for extended periods favor these diseases. Symptoms of both diseases are leaf spots of varying size. Microscopic identification of the acervulus is required to distinguish from Septoria leaf spot. Control consists are proper watering so that leaves are not wet for extended periods. Management is the same as for Septoria leaf spot.

Powdery Mildew of Rudbeckia
The presence of a white "powder" on leaves makes diagnosing powdery mildew easy . Erysiphe cichoracearum and Sphaerotheca fusa are the causal agents of this disease. Yes, there are actually two fungi, both of which cause powdery mildew! Powdery mildew is more likely to appear in mid- to late summer when cool evenings are followed by warm, humid days. In severe instances, if left untreated, powdery mildew can cause leaves to turn yellow, die and fall off. In most instances, it is only an unsightly nuisance.

Management of powdery mildew is slightly different than leaf spot management. Provide adequate air circulation with proper thinning and spacing of plants. Remove and destroy infected leaves and flowers, and avoid fertilizers high in nitrogen that promote new growth, which is more susceptible to infection. Control may also be achieved with the use of fungicides applied as soon as symptoms are visible. Among the compounds registered for use are potassium bicarbonate*, ultra fine oil*, sulfur*, triadimefon, or thiophanate-methyl fungicides. As always, consult the label for application instructions.

Angular leaf spot of Rudbeckia cv. 'Goldsturm.'
This is an unusual disease of Rudbeckia, caused by Xanthomonas spp. Although rarely killing the plant directly, the results are so aesthetically unappealing that most homeowners opt to kill the plant themselves! Symptoms appear as angular, brown spots on the leaves that may cover the entire leaf. Symptoms begin on the lower leaves first and progress up the stem. Control strategies are aimed at prevention, namely, using other "generic" cultivars of Rudbeckia, which are less susceptible to this problem. In the fall after the first hard freeze, remove all above ground plant tissue. Tools should be disinfested with 10% household bleach, 70% alcohol, or one of the commercially available compounds, like trisodium phosphate (TSP) or Phyton 27. In the spring, apply a copper-based* bactericides (Bordeaux, Kocide or Phyton 27, to name a few) to minimize the possibility and severity of infection. It is important to remember to avoid overhead watering since these bacteria are easily spread in splashing water. If you wish to plant susceptible cultivars, starting with clean seed or healthy transplants is may prevent infection from becoming established.

Aster Yellows of Rudbeckia
The pathogen, a phytoplasma, is a bacterium-like organism without the cell wall. It infects the phloem of susceptible plants and causes a general yellowing and dwarfing symptom. As the phytoplasmas reproduce, they consume the plant's food supply. A side effect of this is that the hormonal balance is destroyed. The symptoms that result from this are witches'-brooms, flowers appearing out of the "cone" and leaves sprouting from flowers. The phytoplasma is spread by a leafhopper vector.

Management options are limited to "search and destroy": Infected plants should be removed thrown away. Early season control of the leafhopper vector and removal of weed hosts may help prevent re-infection. Aster yellows has an exceptionally large host range that includes purple coneflower, aster, marigolds, goldenrod, cosmos and other members of the daisy family (Compositae).

*denotes organically accepted pesticide.

Please check out the new diagnostics web pages at
http://www.extension.umn.edu/projects/yardandgarden/diagnostics/

Editorial Notes

Tamarix ramosissima Tamarisk, or salt cedar Photo credit: Beth Jarvis

Someone recently purchased a tamarisk only to discover it's considered to be a weed in the southwestern part of the country. Perhaps one of the benefits of coping w/our Minnesota winters is that such weather keeps some plants from becoming weeds--water hyacinth does not clog our lakes, kudzu is no problem, nor is eucalyptus or maleluca.

So what do you do when a planting doesn't thrive where it's planted, or needs to be moved for some other reason? A common question is how to move established trees and shrubs. Starting in October and wrapping up in November, Gary Johnson, Urban Forestry specialist, will look at the subject from all angles, when it's worth it, what the risks are. Then, he'll discuss what you should do this fall for something you'd like to move next spring.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/. Our home page has clickable links to most of the components of the Yard & Garden Line, such as Bell Museum of Natural History, INFO U and the Soil Testing Lab.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

If you have gardening questions, please call the Yard & Garden Line at (612) 624-4771.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

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