Plant Health Clinic Newsletter #10 May 6, 2009

The weekly plant health clinic newsletter is available here.

Inside this edition you will find information about Photinia leaf spot, Elm black spot, Slime flux in trees, Botrytis blight on Heuchera and Mummyberry blight on Blueberries.

As always you can get more help with diseased plants from your local county extension office.

Plant Health Clinic Newsletter #9 May 1, 2009

The weekly Plant Health Clinic Newsletter is available here.

Inside this edition you will find information about Aphid Damage to Iris, Glyphosate Injury on Tomatoes, Anthracnose on Ash, Maple, and Sycamore, and Patch diseases of turf.

As always you can get more help with diseased plants from your local county extension office.

Plant of the Week: Goldenseal (Hydrastis canadensis)

Shade gardens present an opportunity to grow a wide variety of plants native to the forested woodlands of eastern North America. One of my favorites is goldenseal (Hydrastis canadensis), a plant more commonly thought of as a medicinal herb than a garden ornamental.

Goldenseal is an herbaceous plant that rises from the ground each spring from a tight clump of yellow rhizomes. It reaches about a foot tall when fully grown. A single forked stem arises from the terminus of each rhizome and produces a pair of celery-green leaves in early spring. The pubescent leaves are displayed flat on top with five prominent lobes and can be as much as 10 inches across.

In mid-spring an inch-wide white apetalous flower consisting of a dense cluster of stamens appears at the fork between the two leaves. Following the flower in July is a ball-shaped red berry about 1.5 inches across. Goldenseal belongs to the buttercup family and is monotypic, with only one closely related species occurring in Japan.

Goldenseal has long been used in herbal medicine. Native Americans – including the Cherokees – used the root as a treatment for cancer and to treat localized lesions. Modern medicine has identified the drug berberine (and several others) in the root extract. Berberine, which is produced by several other plant species, has been shown to have antibiotic properties.

Though traditional medicine feels there is little scientific evidence to support its use as an herbal remedy, modern herbalists disagree. It's the sixth most common drug used in herbal preparations.

Plants for drug extraction have been collected from the wild in its native range – primarily high ground from southeastern Canada and through most of the eastern woodlands – for more than two centuries. Because of over-collection, it is becoming rare in the wild and has been listed as threatened or endangered in some states. Fortunately, the herb is easy to grow, and commercial plantings are now common throughout its native range and in the Pacific Northwest. Plants large enough to dig are produced in five to six years from rhizome divisions, while it takes six to seven years for plants grown from seed.

In the garden, goldenseal is easy to grow in any moderately moist and well-drained soil supplemented with an abundant supply of organic matter. It mixes well with other woodlanders, such as Solomon seal, bloodroot, mayapple and trilliums. Plant it in patches along the woodland path or in clusters, where the bold leaf display can be enjoyed.

For more information about horticulture or to see other Plant of the Week columns, visit the Cooperative Extension Service Web site, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.

Bus tour, pest clinic to highlight horticulture field day

Gardeners and fruit producers can learn the latest production techniques and the latest research into pest issues at the 2009 Horticulture Field Day on June 18 at the Southwest Research and Extension Center at Hope.

The event is aimed at gardeners and fruit producers, whose numbers in southwest Arkansas are growing, according to Dr. Vic Ford, center director.

"A highlight of the field day will be a bus tour of the center's horticultural research into blueberries, blackberries and peaches," Ford said. "But we'll also discuss ornamentals, tomatoes and other vegetables."

Extension and research personnel will discuss several topics, including these:

• Common Arkansas weed identification and management
  
• Landscape shrub pruning
  
• Update on blackberry and peach breeding
  
• New-planted blueberry maintenance
  
• How to set an insect trap and identify insect damage
  
• How to build a compost pile
  
• Grow hardy kiwi and blackberries in high tunnel growing systems
  

Gardeners and producers may find the pest clinic after the tour will be the most interesting part of the field day, Ford said. Gardeners are urged to bring specimens from their home gardens or lawns for diagnosis and suggestions for correcting the problem.

At 6:30 p.m., a barbecue dinner will be served for an $8 charge. Participants can pay the day of the event. Ford is asking people to RSVP by June 12. You can call (870) 777-9702 or contact us by email.

For directions to the station and more about our ongoing research visit our web site.

The Cooperative Extension Service is part of the U of A Division of Agriculture.

This activity is open to all interested persons without regard to race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status. Persons with disabilities who require alternative means for communication of program information should notify the county extension office (or other appropriate office) as soon as possible prior to the activity.

Anthracnose affecting shade trees statewide

Recent cool temperatures and frequent rainfall have created ideal conditions for anthracnose plant disease on several common shade trees, says Dr. Steve Vann, assistant professor/extension urban plant pathologist with the University of Arkansas Division of Agriculture.

"Anthracnose of our shade trees may be caused by several fungal organisms that usually cause a variety of leaf spots and twig lesions," says Vann. Maple, sycamore, dogwood and ash trees are especially susceptible. Trees usually react to the disease by dropping infected leaves, much to the dismay of many homeowners.

Maple anthracnose produces dark brown to black greasy-colored spots on the leaves. These spots are usually block-shaped and may have a yellow area, or halo, surrounding the spot. "Numerous spots may grow together and give the leaf a tattered look," says Vann. "These spotted leaves readily fall to the ground."

Sycamore anthracnose is caused by a similar fungus that causes premature leaf drop and may kill young twig tips. Diseased twigs may resemble frost injury, says Vann. These young, newly expanded leaves will often die and droop on the twigs, which may also die and remain on the tree. "On older sycamore trees, the fungus tends to kill leaf tissues alongside the major veins of the leaf blade, giving it a 'netted' look," he says.

Both fungal organisms produce microscopic seeds called spores. These may be carried on wind currents or splashing water droplets to other leaves and twigs, especially if there is an extended rainy period in the spring. Anthracnose fungi typically over-winter on infected twigs and leaves. Dead leaves that don't fall from the tree during the fall and winter seasons can serve as sources of infection the following spring.

"As drier weather returns, infections begin to diminish and trees will often put on a crop of new leaves," says Vann.

Maple and sycamore anthracnose are usually a minor concern for homeowners since occurrences of the disease are generally sporadic, he says. However, if the diseases occur for several successive growing seasons, the tree's health may be compromised.

If a homeowner wishes to have a "specimen" tree in the landscape, it may be necessary to spray with an appropriate protectant-type fungicide in the spring, just before buds break, says Vann. Multiple applications may be required during the growing season to keep the tree disease-free, so complete coverage and the timing of applications are crucial to its effectiveness.

"Waiting until after leaf emergence is usually too late to protect the leaves during the season," says Vann.

A stressed tree is often more susceptible to disease. Trees should be watered and fertilized properly based on a recent university soil test to encourage vigorous growth.

Spraying taller trees may not be practical or feasible for homeowners, thus a professional applicator should be consulted in these cases. Always read and follow the label directions for fungicides when considering their use.

Promoting good plant growth is an integral part of disease management, but a misdiagnosis can still be deadly for any homeowner's shade tree. "Correct disease identification is the single most important first step in designing an effective plant disease control program," says Vann.

For more information on anthracnose diseases found in trees and ornamentals, contact your county extension office or visit our Cooperative Extension Service web site. The Cooperative Extension Service is a part of the University of Arkansas Division of Agriculture.

Plant of the Week: Wild Gingers (Asarum canadense)

In my shade garden grow several wild gingers, members of the genus Asarum. Over the years, most have spread happily, wheedling their way into nooks and crannies around the garden and into my affection as well. Based on the amount of scientific ink that has been spilled on this group of lowly plants, I'm not the only one who has found them intriguing.

Asarums are temperate groundcovers of the northern hemisphere and occurs widely in North America, Europe and Asia. They belong to the small tropical birthwort family (Aristolochiaceae) that's best known for its unusual "Dutchman's pipe" flowers. The Asarums apparently originated in Asia but had spread across the ancient landmasses before the continents went their separate ways.

The most common and prolific of my wild gingers is Asarum canadense. It's a 6-inch tall creeping groundcover that spreads by means of fleshy, pinkie sized rhizomes, eventually forming colonies several feet across. It produces heart-shaped, deciduous 4-inch wide leaves that appear in early spring and persist until the first hard freezes of fall.

Asarum flowers appear in early spring with the new leaves, but they're easily overlooked because they emerge buried beneath leaves and other debris of the forest floor. They're borne singly at the end of a rhizome and are ½-inch long and wide, fuzzy, brown in color with three reflexed sepals. Though interesting, they're not all that showy.

But amongst botanists, the flowers have caused lots of controversy. Structurally, the flowers are arranged in such a way that it's obvious there should be something out there cross-pollinating them. Everything from slugs to fungus gnats have been proposed, but current research indicates most species are self-fruitful, only rarely being cross-pollinated.

When successfully pollinated, the flowers produce seeds which have a nutritious oily coating called an 'elaiosome' which ants find irresistible. The ants carry the seeds back to their nests, enjoy their feast and discard the seeds where they come up willy-nilly in the garden.

Botanists have had difficulty defining the limits of the wild ginger genus. The splitters consider only 20 or so species to belong to the genus Asarum, relegating the other 60 species to three separate, closely related genera. The lumpers though seem to be winning the day and modern classification schemes recombine the groups as separate subgenera within the Asarum genus.

Wild gingers have a long list of ethnobotanical uses, not the least of which is as a substitute for the tropical ginger root. Wild ginger has a similar taste to tropical ginger but is only about one third as strong. In addition to its culinary use, it was also used as a part of the Native American pharmacopoeia, treating everything from infections to various kinds of internal ailments. Meriwether Lewis, probably under the instruction of Sacagawea, pounded the roots and leaves of wild ginger to form a poultice which they applied to Joe Potts' swollen and inflamed leg which he cut with a knife in Idaho's Bitterroot Mountains. He quickly recovered.

But in 2001, the Food and Drug Administration issued a warning against using wild ginger in cookery or as an herbal remedy due to the presence of aristolochic acid, a substance known to cause kidney failure and possibly cancer.

Wild gingers do well in moist, fertile woodland soils where they can grow undisturbed. Most are hardy from zones 4 to 8. They're ideal for use along walkways, in woodland rock gardens or as a groundcover. Once established, they're tough, thrive without special care and persist for many years. Clumps can be divided in early spring.

In Japan, wild gingers are collected by enthusiasts for their colorful mottled foliage and unusual but showy flowers. One nursery is offering more than 30 cultivars of these unusual gingers for hobbyists who're looking for a pot plant that's easier to grow than an orchid and can be left outside over winter.

For more information about horticulture or to see other "Plant of the Week" columns, visit extension's Web site, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.

Plant of the Week: Pearlbush (Exochorda racemosa)

During the 20^th century, American gardens went through a transformation towards greenness.

A century ago, the shrubs in most American gardens were leafless in winter with spireas, lilacs, flowering quince, mock orange and forsythia being common. Evergreens such as yews and junipers began more common early in the century but azaleas and hollies didn't appear until mid-century.

Pearlbush, though no longer common, was one of the deciduous shrubs of this bygone era.

Pearlbush (Exochorda racemosa) is a member of the rose family and most closely related to the spireas, except pearlbush has a larger flower more reminiscent of an apple. It's a large shrub, growing 12 feet tall and wide, with thick, brown stems and a coarse overall texture.

Four species are known, with two in China and two in adjacent areas of central Asia.

Leaves appear early in the spring before flowering and are a medium green, whitish beneath, and 2- to 3 inches long. Unfortunately they don't produce any fall color. Odorless, pure white flowers are 1.5 inches across, five-petaled, with each petal narrowing at the base and produced from a cuplike calyx appear in mid-spring. Flowers are produced on a raceme at the end of each branch and, just before they fully open, resemble a strand of pure white pearls.

The name Exochorda comes from a cord (exo, or
outside, and chorde, a cord) that forms around the developing ovary, producing a dry fruit with five prominent ridges when it ripens in the fall. Though not invasive, it occasionally produces a seedling under its branches.

The common pearlbush is probably too large for most American gardens, but one of its hybrids, E. x macrantha 'The Bride' is more worthy. It grows only 3 feet tall and wide and is covered in pure white flowers each spring.

The venerable old nursery owned by Victor Lemoine of Nancy, France, introduced it about 1900. His son Emile probably did the actual breeding work. This firm was responsible for hundreds of lilac introductions and many of the still common mock orange, spirea and forsythia clones still grown today. It was probably the most important firm for new plant development in the world during the last third of the 19^th century.

Pearlbush is hardy from zones 4 through 8. Because it's relatively nondescript, except in flower, it's best used as a part of the shrub border or, in the case of 'The Pearl,' in the foundation planting. Plants should have at least six hours of sunlight and do best in a fertile, well drained loamy soil. It is unbothered by insect or disease and is very long lived once established.

For more information about horticulture or to see other "Plant of the Week" columns, visit the Cooperative Extension Service Web site, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.