|Yard & Garden Line News
Volume 5 Number 15 September 15, 2003
Acer pseudosieboldianum-A Japanese-like maple for the North?
Stan Hokanson, Woody Landscape Plant Breeding Program
Japanese maples, Acer palmatum, with their various forms, leaf colors, degrees of leaf dissection, and brilliant fall color are much admired and highly valued garden trees. However, in Minnesota, these beautiful trees largely assume a 'cruel temptress' role in the garden. Their USDA Zone 5 hardiness designation puts them in the 'marginal hardiness' category for the southern third of the state. As such, the species will prosper nicely for several years only to be reduced to a near death appearance after a hard winter. Thankfully, the genus Acer is large, containing a number of species with similarities to the Japanese maple, some with greater cold hardiness. Among these is Acer pseudosieboldianum, commonly referred to as Korean maple or purplebloom maple. Korean maple is a small tree or shrub that is actually classified in the same maple section as Japanese maple. Generally listed as being USDA Zone 4 hardy, the species has been grown successfully in Bismark, ND (USDA Zone 3), suffering no damage at temperatures to - 43º F.
In its native habitat in Manchuria, Korea, and China, Korean maple grows in mixed forests on well-drained, stony soils where it can attain a mature height of 15-25 feet with greater width. The species is an openly branched tree with gray, black striped branches. The oppositely arrange, doubly serrated leaves emerge with a reddish tinge that turns to a dark green above with a slight white pubescence on the undersides. The leaves, 4-6" in width, are borne on 1-2 inch petioles and generally possess 9-11 lobes. Fall leaf colors have been described as brilliant yellow, orange and/or red color combinations. The withered leaves are retained through the winter, falling off as growth commences in the spring.
Like any garden plant, the species is not problem-free. Although individual trees are reported to be winter hardy in Zones 3 and 4, some seed lots have been found to be considerably less winter hardy. Similarly, while the species has been reported to have vivid fall colors, the literature contains reports of the species displaying muddy greenish-brown fall colors. Like many maples, Korean maple is thin barked, rendering it susceptible to mechanical damage and winter sunscald damage, the latter most often occurring at the site of mechanical damage. Mechanical damage to the trunk and stems can also provide sites for disease infections. Currently, the main liability of the species appears to be it's susceptibility to a canker disease (Nectria, Eutypella, Valsa and/or Cryptosporiopsis) which enters the tree at wound sites, causing dieback of the infected branches or stem. Fungicides can be used in conjunction with pruning or at wound sites to protect against infections, although there are no fungicides labeled for such use. The principle management strategies include maintaining plant vigor with adequate water and fertilization and the removal and destruction of infected twigs and limbs to prevent the spread of additional inoculum.
While the species tolerates full sun and wind with only minor leaf burning and tatter, it performs much better with protection from afternoon sun and prevailing winds. The species will grow perfectly well in heavy shade, but will develop its best fall color when sited in sunnier locations. The Korean maple would be best used as a focal point in a naturalized garden in company with low growing ferns and shade tolerant perennials. I can also envision the tree planted with smaller statured rhododendrons such as the R. dauricum hybrids, the PJM hybrids and/or Korean (R. mucronulatum) hybrids.
Acer pseudosieboldianum can be reliably grafted on A. palmatum. We have had some success rooting terminal softwood cuttings collected in June and treated with 8000 ppm IBA. The species can also be grown from seed, although locating viable and true-to-type seed can be difficult. Several subspecies, and varieties of A. pseudosieboldianum have been named in the literature, so some effort may be required to verify the identity of plant material acquired from commercial sources. A search of the Minnesota Landscape Arboretum's online plant and seed source locator (http://plantinfo.umn.edu/sources/default.asp) revealed five sources for seed and numerous sources for plants, including Bachman's Nursery Wholesale as a local source.
In the Woody Landscape Plant breeding program at the University of Minnesota, we have been evaluating a small collection of Korean maple seedlings as part of a larger project to assess a number of Asian maple species with potential for use in Minnesota. Programmatic goals include selecting reliably cold hardy seed sources and genotypes that produce consistently good fall color. In addition, we intend to determine the causal agent(s) of the aforementioned canker disease(s) and identify sources of resistance to the pathogen(s).
This article was previously published in the Minnesota Nursery and Landscape Association news letter.
Keep Photographic Record of Landscape Trees and Shrubs
Deborah Brown, Extension Horticulturist
Make time this fall, before the leaves drop, to take photos of the trees and shrubs in your home landscape. If you have a digital camera, you can even put the pictures together on a CD, then shoot new ones every year or two. You never know when one or more valuable trees or shrubs will be storm-damaged or fall prey to some other accident. Having an up-to-date record of what they looked like when healthy and intact will be most helpful when it comes time to collect on an insurance policy or claim a loss for tax purposes.
Nice variegated maple.
According to the International Society of Arboriculture, tree value is based on a number of different factors. First is the kind of tree – is it a tough, hardy tree in your area, or is it more marginal? Is it known for being sturdy, or is it fast-growing and more prone to disease or wind damage? (For instance, a bur oak versus a silver maple or green ash.) What is its size and condition?
Take a close-up of each tree, then step back and take a photo of how it looks in the larger landscape. Some trees may hold greater value because they shade your home from summer sun, act as a focal point in the landscape, or create a sense of privacy from neighboring property or from the street. Others may be less valuable due to their placement too close to one another, or perhaps because they overhang your house or garage. Photos will also show if a tree has been pruned properly and has been well-maintained.
Take individual photos of key landscape shrubs as well as photos of hedges and plant groupings. Though these plants are not valued as highly as established trees, it doesn't hurt to have a record of them, too. Plus it will help determine the overall value of your landscape, and the setting in which the trees function.
If your landscape plants are looking pretty tatty due to this summer's heat and dry conditions, you might prefer waiting until next summer. Either way, do add this activity to your list of household tasks. Then just hope you'll never need to use the photos!
A Cool, Scary Insect
Jeff Hahn, Assistant Extension Entomologist
What is wasp-like, shiny black, two inches long, and very slender? The answer is a pelecinid (pel-ah-SIN-id) wasp. You can recognize this insect by its large size and conspicuously long abdomen. This wasp belongs to the family Pelecinidae of which there is just one species present in North American, Pelecinus polyturator. Virtually every pelecinid wasp you see is a female. Males, about half the size of females, are rare and usually not seen.
Photo credit: Jean Forrey
Adult wasps emerge from mid to late summer. This wasp is a parasite of the white grubs of June beetles. It uses its long abdomen to probe into the soil until it reaches larvae to lay its eggs. However, finding a pelecinind wasp in your yard does not necessarily mean you have grubs in your own yard. It is most likely just incidental as they can fly in from nearby areas.
Despite its impressive abdomen, a pelecinid wasp does not have a stinger. If captured it can use its abdomen to jab at its captor to protect itself although it would rarely be able to break human skin. Pelecinid wasps are unaggressive towards people and for all intents and purposes are harmless to us. If you see one just ignore and let it go on its way.
Jeff Hahn, Assistant Extension Entomologist
Yellownecked caterpillars, Datana ministra, are found in the eastern U. S., including Minnesota, from mid to late summer. Adult moths emerge during June and July from pupae in the soil. Soon afterwards, female moths lay clusters of 100 or more eggs on a wide variety of trees and shrubs, including oak, birch, elm, maple, crab apple, walnut, mountain ash, honeylocust, and sumac.
Yellownecked caterpillar, black-yellow phase
Photo credit: Jeff Hahn
These eggs hatch in July or August. The larvae have a black head with a striped body and fine white hairs. Yellownecked caterpillars get their name from the orange yellow rectangular spot behind their heads. They have two color phases, black with orange yellow stripes and orange yellow with red orange stripes. At first young caterpillars skeletonize leaves. As they become older, they consume the entire leave except for the petioles.
These caterpillars are gregarious, feeding together in nonsocial groups on branches. When they finish defoliating one branch, they will move to an adjacent branch to continue to feed. When disturbed, yellownecked caterpillars will arch their heads and the tip of their abdomens, forming a ‘U'. They try to appear threatening, particularly to ward off natural enemies, such as fly and wasp parasites.
Yellownecked caterpillars feed for about four to six weeks into August and September.
Mature caterpillars are about 2 inches long. When they're done feeding, they move down to the ground and pupate about two to four inches in the soil where they remain until next summer. There is one generation a year.
Photo credit: Jeff Hahn
Yellownecked caterpillars are occasional pests of shade trees, although are not considered a serious forest problem. Generally this insect is not widespread but can occur in high numbers and cause heavy defoliation on individuals plants or in localized areas. Fortunately, this kind of damage has little effect on healthy, mature trees at this time of the year. There are also a number of insect predators and parasites as well as birds that help reduce yellownecked caterpillars numbers.
In most cases, it isn't necessary to treat yellownecked caterpillars as trees can easily tolerate their defoliation. If it necessary, monitor trees in July and treat them with a registered insecticide when they first hatch and the caterpillars are small.
Get the low down on this month's insect pests at
Avoid Blue Spruce Abuse
Janna Beckerman, Extension Plant Pathologist
Colorado blue spruce (Picea pungens) is the most popular conifer in the United States. Planted to the point of monotony, one would be hard pressed to drive down any street in any neighborhood and not see its stately shape and silver-blue hues gracing a yard as a specimen tree, or serving as a windbreak. These trees bear little resemblance to the wind-whipped character-laden (or grotesque) counterparts of the middle and upper slopes of the Rocky Mountains. Despite the care and nurturing of industrious homeowners, when grown in the Midwest, Colorado blue spruce lives a greatly shortened life "in urban captivity."
Spruce gall, caused by the Cooley spruce gall adelgid, is commonly diagnosed as a disease problem while the dying inner needles, caused by Rhizosphaera, are often overlooked.
Yard & Garden Clinic
Rhizosphaera needlecast disfigures and kills Colorado blue spruce.
symptoms of cytospora canker.
Plant Disease Clinic
Colorado blue spruce is commonly afflicted by winterburn.|
Every year, the Yard and Garden Clinic receives hundreds of phone calls regarding the health of their Colorado blue spruce. Trees that were previously considered healthy, or given no consideration at all, "suddenly" develop unusual colors with dying sections, usually at the top. In many instances, diseases, insects or neighbors are blamed for the declining tree. And in some instances, one or more factors may be involved. Colorado blue spruce is attacked by spider mites, galls, needlecasts and cankers (in addition to the chemical wielding neighbor). However, the most common reason for unhealthy spruce is the simple fact that they should never have been planted in Minnesota in the first case.
When planting Colorado blue spruce, homeowners need to recognize that their tree has a lifespan of approximately 30 years if they are lucky! The greatly reduced lifespan of this tree is due to the fact that this Rocky Mountain tree is not at homes in the Northern Great Plains. Colorado blue spruce suffers under our hot, humid summer conditions. If that wasn't bad enough, drying winter winds with limited snowfall (compared to the mountains) exacerbates the drying conditions and pulls moisture out of needles, resulting in dessication and winterburn. Finally, the fact that our temperatures can fluctuate from subzero to thaw and back results in losses of winter hardiness, premature budbreak and tip death or insufficient hardening off when winter arrives.
If our environmental conditions weren't unsuitable enough, there is the issue of soils. Rocky mountain soils are, as the name suggests, thin and rocky, with a low clay content. Contrast this to much of Minnesota, which is heavy clay. Heavy clay is slow to thaw, preventing water from reaching needles that are ready for a drink when spring arrives. Heavy spring rains on a heavy clay soil results in flood damage or even failure of the entire root system.
What can be done for declining Colorado blue spruce? Much to the frustration of homeowners, the correct answer is "Nothing." Few fungicides are labeled for control of spruce diseases, and most of these act as protectants. This means they will not cure existing problems. Furthermore, most problems are cultural, not insect or disease. Chemical management will not solve these underlying problems.
This leaves (or needles!) us with limited options. Conifers add so much to the winter landscape, it's hard to let go of the Colorado blue spruce. So, what can you do to replace that blue spruce? Here are a few suggestions:
Black Hills Spruce/White Spruce (Picea glauca var. densata). A shapely "Christmas" tree with short, blue-green needles of unpleasant scent. Useful as both specimen or windbreak. Resistant to cytospora canker, more resistant (but not immune) to Rhizosphaera needlecast (Fig. 3).
Serbian spruce (Picea omorika) - A good, but narrower substitute for the Colorado blue spruce, this plant grows taller than 50 feet with glossy green needles and graceful, pendulous branches. Because it is still relatively uncommon, little is known about its disease susceptibilities.
Larch (Larix spp)-Numerous cultivars provide a multiplicity of size and shape, including weeping and dwarf forms (and even dwarf, weeping forms). Remember that larches are deciduous conifers-that means they are supposed to change color and drop every fall, unlike Colorado blue spruce!
Swiss stone pine (Pinus cembra) - This pyramidal, long-needled white pine will grow to 40 feet. It makes a beautiful specimen or focal point, produces edible "nuts" for use in pesto, but is susceptible to white pine blister rust, and sphaeropsis shoot blight.
White fir (Abies concolor) - Although it is the best fir for this area, it needs to be planted in a protected sight. Summer heat and drought can adversely affect it like Colorado blue spruce, so it should be planted in morning sun in evenly moist soil. At 25 to 50 feet, this fir forms a stately pyramidal shape and features curving blue-green needles that smell of tangerine.
White-cedar or arborvitae (Thuja occidentalis and cultivars) - Use it as a specimen or as part of a living screen. This tree makes a formidable hedge, and is tolerant of heavy clay soils. We have seen very few disease problems associated with these trees, however, it's western counterpart, Thuja plicata, is very susceptible to winterburn.
Chinese juniper (Juniperus chinensis) - Not as large as pines, spruces or firs, a few of the upright junipers can grow to 25 feet tall and are useful landscape plants. Some have blue-green, or even green-gold needles. Recommended cultivars include J. c. var. sargentii 'Glauca', 'Old Gold' and 'Aurea'. Although resistant to cedar apple rust, it is susceptible to several blights.
Rocky Mountain Juniper (Juniperus scopularum)-Reaching only 20', this tree is still not as large as pines or spruce, but its beautiful steel blue foliage and columnar form makes this a prime, but underutilized specimen. Although generally resistant to cedar apple rust, it is susceptible to several blights. Cultivar 'Grizzly Bear' is very hardy and relatively winterburn resistant.
Mid-September Garden Tips
Beth Jarvis, Yard & Garden Line
Compiled from conversations with Bob Mugaas and Doug Foulk, Regional Exension Educators, and Gary Johnson, Urban and Community Forestry.
Red currants trained on wires at Univ. of British Columbia, Canada.
Photo credit: Beth Jarvis
Mid September is prime time for broadleaf weed control (dandelions, creeping Charlie, clover, etc.)
You don't have to wait for a frost. As the days get shorter and the temperatures drop, the plants start to move photosynthates from the leaves into the roots. They move herbicides together with the photosynthates. Read the label for specific temperatures, but generally herbicides are effective as long as the daytime temperatures are in the 60s as the plants are still growing.
If you seeded your lawn this fall, keep the leaves off the new grass to maximize the amount of sunlight on the new grass.
Mid-Sept. is a fine time to core aerate. Grass needs 6 weeks to recover before winter sets in.
Vertical mowing/power raking chores should be completed by next week as the grass needs to recover before winter.
You're running out of time to seed grass. If you bought seed, apply it now.
Keep watering fruit plants. Newly planted trees and shrubs, and blueberries and strawberries are especially susceptible to drought stress.
You can't tell if grapes are ripe until you taste them Color is no indication of ripeness.
To tell if your apples are ripe, you have to taste them as well. Apples will not ripen well once they're picked. Skin color is never a good indicator, though dark seeds are. If they taste they way they ought to, go ahead and pick them. If they still taste a bit starchy you can pick, but realize they won't improve.
Trees and Shrubs:
Keep watering trees and shrubs. See last issue for details. http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Sept0103.html#water
Unmulched planting should be watered first, then mulched. Once watered, surround plants with 2-4 inches of mulch. Use 2" of finely textured mulch and up to 4" of coarsely shredded wood chips. Keep mulch 2" away from the trunks of the trees.
Now is the time to schedule an arborist to come prune your oaks next winter. To get the best people, call early.
If you're planning to revamp your landscape, now is a good time to root prune any small trees or shrubs you plan to move next year. See details in:
If you've previously root pruned, now's a great time to get those plants moved. (And watered and mulched.)
Fall's a great time to plant containerized stock. Remember to water and mulch.
Don't move pines, especially white pines after the end of September. They need more time to become established.
As perennials start to turn yellow, it's ok to cut them back. Destroy any infected plants and compost any healthy foliage.
Water and mulch perennials. We lost lots of plants last winter beause the soil was so dry and the frost went deep.
Spot spray or paint weeds in perennial beds with glyphosate herbicide (eg: Round up).
Bring houseplants in as nights cool. Be sure to keep them isolated until you know they're bug free.
In October, we return to monthly publication. Dave Hanson, Urban and Community Forestry, will provide the truth about tree roots Do they heave sidewalks, see out sewer pipes and imperil basement walls?
Quarry at Butchard Gardens, BC.
We'll visit the North Central Research and Outreach Center (ROC) in Grand Rapids sometime this fall/winter and another "experiment station".
For February 1, Peter Moe, Minnesota Landscape Arboretum, will write about a day in the life at the "Arb" and what it takes to keep it looking so good.
Looking ahead, after Christmas, Dave Ragsdale will expound on the changing face of insecticides. Scientists are finding new insecticides that are more narrowly focused to target specific pests. The general purpose, broad specturm, ecologically harmful insecticides may one day be a thing of the past.
In the future, you'll also get to meet Dr. Tim Kurtti, who does deer tick research.
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.
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