|Yard & Garden Line News
Volume 4 Number 12 August 1, 2002
New Woody Plant Introductions from the U of M
Nancy Rose, Scientist, Horticulture Research Center
If you've ever delighted in the exquisite spring blooms of the Lights Series azaleas, or admired the bright cherry-red winter stems of 'Cardinal' dogwood, then you've seen some of the work of the University of Minnesota's woody plant research project. This project has many facets, but perhaps the most notable for northern gardeners has been the introduction of hardy ornamental trees and shrubs.
The selection, naming, and introduction of new landscape plants is a multi-year process, often taking ten to twenty years from start to finish. Once we identify a promising plant in our research nurseries we must vegetatively propagate it so that we then have clonal (exactly the same as the original plant) material for further evaluations. If this selection continues to rate highly in our evaluations for traits such as winter hardiness, insect and disease resistance, and ornamental qualities, it may be considered for naming and introduction.
In the past year or so we've named a number of new ornamentals and they have all been approved for introduction. It will be several years before you will see these plants for sale at your local garden center, but here's an early look at some of the new introductions.
Acer x freemanii FirefallTM
FirefallTM Freeman maple is a large shade tree that will provide outstanding fall color in northern regions. This interspecific hybrid cultivar resulted from a controlled cross of a cutleaf silver maple (Acer saccharinum 'Bebe') and a red maple (Acer rubrum 'Autumn Spire', a University of Minnesota introduction). FirefallTM has an upright-oval form with good branch angles. It will probably reach 40-60 feet tall and 30-40 feet wide at maturity. This selection is male and therefore does not produce nuisance seeds. The foliage is an attractive medium green through the summer. Fall color is bright orange to scarlet and develops fairly early, around late September to early October. This is a distinct advantage over some existing Freeman maple cultivars that color later and often don't develop much color in northern regions before freezing temperatures cause the foliage to drop.
Cornus hessei Garden GlowTM
Cornus hessei Garden GlowTM is a shrub dogwood with unique chartreuse to gold colored foliage. The species Cornus hessei is similar to Tatarian dogwood (C. alba) but of a smaller size, and Garden GlowTM seems to have a mature height of under 5 feet. This smaller size makes it more manageable in residential landscapes. Garden GlowTM bears clusters of small white flowers in the spring, followed by white to pale blue berries in late summer. This attractive shrub has the best yellow-green leaf color when planted in light shade. If planted in all-day full sun the golden leaves tend to develop bleached, sunburned spots. Garden GlowTM may develop some reddish pink fall leaf color, and it shows attractive red stems during the winter.
Rhododendron Lilac LightsTM
A new addition to the Lights Series of hardy deciduous azaleas, Lilac LightsTM is an improved version of 'Orchid Lights'. Like 'Orchid Lights', Lilac Lights™ resulted from a controlled cross of Rhododendron canadense and a Mollis hybrid azalea (Rhododendron x kosteranum). Lilac LightsTM is fairly low growing, maturing at about 3 ˝ feet tall and 4-5' wide. This azalea blooms in mid to late May with numerous lax trusses, each holding 8-10 flowers. The corolla is 5-lobed: lower lobes are narrow and deeply divided, while the upper three lobes are less deeply divided. Flower color is medium pinkish purple with darker speckles on upper lobes. Flowers are not fragrant. Foliage is medium green.
Rhododendron Candy LightsTM
This new cultivar restores pink to the color palette of the Lights Series of hardy deciduous azaleas. An earlier cultivar, 'Pink Lights', proved to be difficult to propagate in commercial quantities and so is not widely available. Candy LightsTM results from a controlled cross of Rhododendron atlanticum and a red-flowered Mollis hybrid azalea (Rhododendron x kosteranum). Candy LightsTM is a medium sized shrub, growing 5-6 feet tall and wide. It blooms in mid to late May with many dome-shaped flower trusses, each holding 8-10 flowers. Flower color is a clear light pink, with pale yellow streaks on the upper corolla lobe. Flowers have heavy substance and are strongly fragrant. Foliage is medium to dark green.
Maackia amurensis SummertimeTM
This selection of Amur maackia is an excellent small tree with multi-season interest. SummertimeTM grows as a low-branching single-trunked tree, reaching a height of 18-20 feet and a width of 12-15 feet. When the compound leaves emerge in spring they have a distinctive silvery appearance. Leaves mature to a rich deep green color; this clean green foliage is retained until leaf fall. Summertime™ Amur maackia blooms in mid-late summer, usually late July to early August. It produces numerous bottlebrush-like racemes of small cream-colored flowers which may last for a week or more. Small (2-3 inch long) papery seedpods develop and turn brown in fall. Because of their relatively small size the pods do not present a litter problem in the landscape. The bark of this small tree is mottled olive green to golden brown and provides some winter interest.
In the Future
We have a number of other woody ornamentals in the pipeline for introduction. Project scientist and plant breeder Kathy Zuzek has been hybridizing and evaluating shrub roses for more than 10 years. Out of the many thousands of rose seedlings produced, she has selected and numbered over 200 plants that show promise. Many of these will simply be used as parental material for furthur breeding, but several look like good candidates for introduction. Nine of these rose selections are currently being grown in regional trial sites around the state. Evaluations from these trials will help decide which roses make the cut.
Work on the hardy deciduous azaleas continues. One color that's missing from the Lights Series so far is red, and we're looking at several good red-flowered azaleas for introduction in the near future. Project leader Dr. Stan Hokanson likes one of our advanced selection azaleas that has double flowers in a pink-coral shade, so there may be a 'Double Lights' down the road a bit.
Another possible introduction is a selection of the large native shrub known as nannyberry (Viburnum lentago). This selection was made by project scientist Steve McNamara who noticed that this individual plant was remarkably free of powdery mildew, that annoying fungal leaf disease that often whitens the leaves of susceptible plants in late summer. With increased interest in well-adapted native plants we hope there may be a market for this type of introduction.
Plan to Seed New Lawns
Deborah Brown, Extension Horticulturist
Every autumn people are surprised by what a short window of time we have in which to seed our lawns. In the metro area, seeding should begin in mid-August or early September, but it should be completed by the middle of September. You might stretch that deadline by a week or so in the southernmost part of the state.
Young grass seedlings must grow enough so their roots can carry them through winter and provide the energy needed to sprout again the following spring. If you plant too late, seeds may germinate, but it's unlikely they'll come back strong next year....if at all.
Whether you're starting a new lawn, or replacing a poor section of an existing lawn, you must eliminate weeds and grasses first. Use a product containing glyphosate, such as Round Up. It kills practically all green, growing plants, but won't leave any residual in the soil to interfere with new seeds. If you spray now, in 10 to 14 days you'll be able to add fertilizer, rototill the soil, AND plant your seeds in plenty of time to meet the mid-September deadline.
Getting the Most From Your Garden
Deborah Brown, Extension Horticulturist
Except for the truly dedicated among us, few gardeners are as enthusiastic in the dog days of August as they were in spring, when visions of horticultural splendor danced in their heads and all things seemed possible. Regardless of this year's gardening successes or setbacks, this is not the time to slack off! Despite the discomfort of hot, humid weather and hoards of hungry mosquitoes, you need to hang in there to get the most from your garden. Watering, weeding -- even replanting -- will all result in increased vegetable yields and a showier display of flowers.
Vegetables and flowers.|
It's important to provide a steady supply of moisture to developing plants, particularly in hot weather. Uneven moisture is responsible for blossom end rot, a common malady of tomatoes and sometimes squash, as well. It also causes knobby potatoes and may also influence the flavor of carrots and cukes, rendering them bitter-tasting.
Make a habit of watering thoroughly to encourage deep rooting. Water early in the day, if possible, when temperatures are at their coolest, so less water will be lost through evaporation.
If you use oozing hoses that allow water to seep into the soil, or trickle irrigation that directs water to the base of each plant, timing is less critical. You could even water in the evening, a time we try to avoid with overhead sprinkling. (When foliage is wet at night, it often won't dry until the next morning. This creates an ideal environment for plant diseases.)
Even though most people are less inclined to keep after garden weeds in August, it's as important now as it was earlier this summer. Weeds not only compete with desired plants for moisture and nutrients, they may harbor insects that will feed on them, causing injury and possibly spreading plant disease. And the seeds they produce will remain viable in the soil, ready to sprout, for years to come.
It's okay to incorporate weeds into a compost pile if they're not full of seeds. But if they're loaded with seeds, you probably shouldn't put them in the compost unless it's a good, active pile that heat up well. Otherwise when you use your compost you'll be inadvertently spreading weed seeds.
Though it's too late to plant most vegetables, you can still make use of the spaces where plants are already through producing. Remove all traces of debris from the earlier plants, and work some garden fertilizer into the soil where you plan to replant.
Anything you plant in August must be able to mature in a fairly short timeframe to be of any value. Right now you should be able to seed kohlrabi, leaf lettuce, radishes, spinach and green onions (bulbing onions that you pick while they're still immature.) You can also plant turnips and beets for their greens which should grow quite mild and tasty as cooler weather sets in.
"Deadheading" simply means removing flowers once they fade. This means plants won't waste energy on seed development. Equally important, many plants slow their production of flowers once they've set mature or ripe seeds, so it's to your advantage to prevent seed production if you possibly can.
The same principle applies to vegetable gardens. Be sure to harvest or remove any vegetable that develops from a flower – beans, squash, tomatoes, peppers, cukes, and so forth – to prevent their seeds from ripening which keeps the plants productive.
Ideally, you should pick vegetables just at the stage when they'll be most tender and flavorful, or in the case of tomatoes or melons, when they're perfectly ripe. Sometimes they get away from you though, and become over-mature. You've probably seen snap beans with pods bulging from the large seeds inside, or swollen yellow-orange cucumbers that were hidden beneath leaves and evaded harvest. Even though they're long past their prime, you need to pick them and throw them onto your compost pile.
Pain in the Grass? Ascochyta Blight of Turf
Janna Beckerman, Extension Plant Pathologist
Our extended period of wet weather in some parts of Minnesota has resulted in an outbreak of Ascochyta leaf blight on lawns. Although not previously reported in Minnesota, Ascochyta blight is poised to be a recurring problem on Kentucky bluegrass, and the frequent, heavy rains has certainly made Ascochyta blight a perennial problem this summer. This is the time to be on the look out for pockets of blighted grass, as this disease will continue as long as the wet weather persists. Your lawn may develop a patchy appearance, which has led several area lawn care companies to misdiagnose the problem as patch disease. Further confounding diagnoses is the fact that opportunistic pathogens, like Colletotrichum spp. of turf, may further impact an already bad disease situation. Finally, this disease may occur in conjunction with other diseases, making diagnosis difficult.
Ascochyta leaf blight gives a patchy appearance and allows weeds to invade.
Patch Disease Versus Ascochyta Blight
A key symptom of Ascochyta blight is the presence of healthy leaf blades interspersed amongst the blighted grass. Because leaves begin dying from the tip back, it is important to check the leaf blades for bleached areas on the tips. Unfortunately, frequent mowing may prevent you from observing this important symptom, and actually worsen the disease situation. If the infection has become severe, lesions may occur in the center of the leaf blade, forming a straw-colored band across the leaf that can be confused with dollar spot. Careful examination of the tips or lesions will reveal tiny black fruiting bodies or pustules called pycnidia. Each pycnidium contains thousands of two-celled spores that are released by water and spread by mowing, which, incidently, provides a nice infection court for the fungus to invade! No, this doesn't mean you can use this disease to give up mowing your lawn! However, you would be wise to mow only when your grass is dry-good advice regardless of any disease pressures! There are over twenty species of Ascochyta causing tip blight in turf; however, control strategies are the same for all of them.
Who Gets Ascochyta?
This disease problem has been associated with underlying stress (poor soil conditions, soil compaction, or using dull mower blades that create severe wounds for the fungal spores to enter). However, the fact that we've received samples from high maintenance golf courses, well-tended lawns and even neglected lawns, suggests that the weather is the main culprit. For this reason, preventative tactics that keep your lawn healthy are your best management tool.
There are several approaches to lawn care that should be repeated over and over and over. Don't mow the grass too short--Raise your mowing height 3 inches. Never removing more than 1/3rd of the grass blade at any one mowing. If your lawn is regularly maintained at 3 inches, this means you don't need to mow until your grass is 4.5 inches high. Keep your mower blade sharp. Inspect your blade at the beginning of the year and have the blade sharpened regularly.
Although this disease is usually only a problem when there is too much water, it never hurts to remind you when and how to water! Water infrequently and water deeply-to a depth of 6 inches. Water in the very early morning hours to reduce evaporation (and keep your water in the lawn and not the air) and allow the turf an entire day to dry, thereby preventing disease. During summer avoid applications of nitrogen fertilizer. Fast-release, high-nitrogen fertilize will produce succulent growth that is susceptible to many lawn diseases. If your lawn needs nutrients, select a slow-release nitrogen formulation. Apply 1/2 to 1 pound of actual nitrogen per 1,000 square feet of lawn. Early fall is the best time to apply a slow-release lawn fertilizer.
Healthy blades of grass in infected clumps are a symptom of Ascochyta blight.
Prognosis for Blighted Lawns?
As bad as this outbreak of Ascochyta blight has been, the lawn can and will recover. Severe outbreaks may warrant the use of fungicides, such as those containing the active ingredient myclobutanil, to prevent further spread. If you had an outbreak of this disease this spring, there is a very good chance that a wet fall can provide the conditions to allow the disease to recur. For this reason, it is important to be proactive and repair dead areas prior to the cool weather of autumn.
Dead patches can be reseeded with a variety of resistant cultivars. Although no one variety is labeled as resistant to Ascochyta blight, the incorporation of several varieties prevents the likelihood that all varieties will be infected at the same time and for a new patch to develop should the disease recur! Suggested varieties include 'Adelphi,' 'Park,' and 'Majestic.' In repairing a lawn damaged by disease, it is important to clip the lawn low to get rid of as much dead grass (which may contain the inoculum, or fungal fruiting bodies that cause the disease) as possible. For small patches, use scissors. For larger areas, remove dead grass and leaves near the soil surface with a rake. Be sure to completely expose the surface and loosen the soil in the bare spot. Remember to use your resistant cultivars to reseed your lawn! Lightly press the soil after seeding and keep the seeded area moist until the grass emerges. The use of straw mulch conserves moisture and aids in grass seed establishment. August 15- September 15 are recommended times to begin your reseeding projects!
Jeff Hahn, Assistant Extension Entomologist
Deer flies have been a nuisance in many areas of Minnesota this
year. These flies are a little larger than a house fly and are
stout-bodied. They are colored yellow or black and have dark colored
markings on their wings. Their eyes are often a brightly colored green or gold
pattern. Deer fly larvae live in aquatic or semiaquatic sites, like marshy
areas, streams and ponds. Adults are found near these breeding grounds,
especially along the edges of woodlands but they are strong fliers and can range
miles away from their breeding areas.
Deer flies are most active on sunny, calm days. They have a tendency to
wait in shady areas for a host. Deer flies primarily use sight to find a
host and seem to be particularly attracted to moving, dark shapes. They
typically go for the head and neck when biting people. Deer flies have
been known to chase hosts a limited distance.
They can inflict a painful bite as they seek a blood meal. They use
knife-like mouthparts to slice a wound in the skin and feed on the
resulting blood. Fortunately, deer flies do not vector any disease in
Minnesota, although some people can suffer allergic reactions to the
bites. In addition to humans, these biting flies also attack many
different animals, including deer, horses, and cattle. Deer flies are most
common in June and July, although they do persist until the end of summer.
Unfortunately, our options are very limited when it comes to preventing
deer flies from biting us. It is not practical to control immature deer
flies by eliminating breeding sites, i.e. marshes, streams, and
ponds. There are just too many potential sites to treat and the risk of
environmental harm is too great. It is also prohibitive and impractical to
treat adult flies in yards, parks and others areas with insecticide
Control of deer flies usually comes down to personal protection. Wear
protective clothing, such as hats, long-sleeved shirts, and long pants to
help protect exposed skin. It is more difficult for deer flies to bite
through clothing. Some gardening catalogs sell sticky patches that are
placed on the back of hats. The theory behind it is that the deer flies
will land and stick to the patch before they can bite you. You can also
try a nylon head net, similar to a bee keepers veil.
The use of a repellent (DEET, permethrin) may be able to provide some short term
protection. Products containing DEET may be applied to clothing and skin while
permethrin products may be applied to clothing only. Be careful not to
overapply these products. When using DEET products on children, use as dilute a
solution as possible, usually 10% or less.
Get the low down on this month's insect pests at
Thief Ants are Nuisance in Homes
Jeff Hahn, Assistant Extension Entomologist
Very tiny ants found in homes during mid to late summer are mostly likely
thief ants. Also known as grease ants, they are about 1/20th inch long and are
yellow to light brown. They feed on live and dead insects as well as greasy
foods. Thief ants can potentially cause problems by getting into food but they
are not known to carry any disease and are usually just considered a nuisance.
These native ants are capable of nesting indoors where they are found in
wall voids, cabinet voids, and around baseboards. But more times than not they
nest outdoors, preferring to be in soil under objects like stones or logs or in
the old decaying wood of logs or stumps. Thief ants are usually found near
other ant nests and typically steal the larvae of other ant species for food.
Finding thief ants in homes only during summer usually means they are entering
homes from outdoor nests.
There are several general tactics to consider for minimizing thief
ants. Keep food, especially greasy material, picked up and counters
cleaned. If you can detect how the thief ants are entering (and admittedly this
is easier said than done), you can seal up cracks or spaces to help exclude
them. If you can determine where the thief ants are nesting outside (also
easier said than done), you can treat the outdoor nest directly. You should
tolerate thief ants as much as possible, especially if there are only small
numbers in limited areas in your home. If you ignore them, they should go away
on their own by the end of the summer.
If there are too many thief ants to leave to their own devices, you may
consider treating the home's exterior to help prevent the ants from coming
indoors. One application should be sufficient before they go away on their own.
Homeowners have access to a number of insecticides that are labeled for use
around the outside of buildings, including permethrin, cyfluthrin, deltamethrin,
and cypermethrin. An experienced pest control service can also treat your home
Another option is to bait them with a homemade bait or one you buy from a
store. However, the drawback with baits is that they take time, weeks or
months, to eliminate the ants. Also thief ants don't always seem to take bait
long enough to eliminate their colony.
If the ants do not go away by the end of the summer, it is good idea to
submit a sample to an expert to verify what ant species is present. If it is
thief ants, they may be nesting indoors. Because they are so small, it is
usually difficult to treat thief ants indoors. It is usually necessary to
contact a pest control service to eliminate thief ants.
It is also possible that the problem is Pharaoh ants and not thief
ants. Pharaoh ants looks very similar to thief ants, they are about 1/16th inch
long and yellowish. The feed on a variety of foods but prefers fatty and greasy
foods. To distinguish between them, you have to use a dissecting microscope to
count the number of segments in the antennal club - thief ants have two and
Pharaoh ants have three.
Unlike thief ants, Pharaoh ants are tropical in origin and only nests
indoors in Minnesota. They are often difficult to control because their
small size allows them to nest in many small, inaccessible areas. You
should never spray Pharaoh ants as this causes their nest to fragment,
creating several nests where you only had one before. The best control for
Pharaoh ants is to bait them which is best done by an experienced professional
pest control service.
Mosquito Trap Being Recalled
Jeff Hahn, Assistant Extension Entomologist
(Some of the information for this article was obtained from a news release by
the U.S. Consumer Product Safety Commission (CPCS),
Mosquito DeletoTM is a mosquito trap sold by Coleman that burns propane and emits
a combination of carbon dioxide, heat, and a mosquito attractant (Octenol) to
attract and capture mosquitos. The Mosquito DeletoTM Trap is a component of two
trap versions, the Back Home System and the Portable System. Both traps stand
about two feet high. The traps are used in combination with an inhibitor
(containing linalool) which is placed about 50 feet away from the traps. In
theory, the mosquitoes can’t find you due to the inhibiting linalool and are
eventually attracted to the trap(s) where they become stuck on sticky panels.
Home centers, mass merchandisers, and hardware stores sold these products
throughout the U.S. (except California) from March 2002 to July 2002 for
$170 to $200. However, on July 15, the Coleman Company, in cooperation
with the U.S. Consumer Product Safety Commission (CPCS), voluntarily
recalled about 136,000 Mosquito DeletoTM Traps.
The problem was the mosquito trap's propane regulator can leak propane or
allow an overflow of propane gas, both of which pose a fire hazard to
consumers. In addition, the fuel hose attachment sold with the Back HomeTM
System can become damaged and leak propane, which also poses a fire hazard to
consumers. Coleman has received 28 reports of traps melting or catching on fire
as a result of propane leaking and 7 reports of damage to the propane fuel
hoses. Fortunately, no injuries have been reported.
Consumers should stop using the mosquito traps and propane hoses
immediately and contact Coleman at (800) 257-5299 anytime. For more
information, consumers can log on to the company's website at www.coleman.com.
Despite the claims made about this product and similar traps, there has
been no research to confirm the effectiveness of them. It is unclear that these
traps have the ability to attract mosquitoes from a particular area to the
traps. Jeff Baillan, a reporter with KMSP TV, channel 9 News conducted a
demonstration of a Mosquito DeletoTM Trap. The results showed no difference in
the number of mosquitoes bites on people with and without nearby traps. In
fact, despite following the directions, the Mosquito DeletoTM Trap did not
capture any mosquitoes.
It has been long known that traps using carbon dioxide are attractive to
mosquitoes, but it is doubtful that they can remove large numbers of
mosquitos or reduce the incidence of mosquito disease in a given
area. Don’t be fooled by impressive collections of mosquitoes captured by these
traps; they are very likely a small amount of the overall mosquito population
around the traps.
Also consider the cost of such devices. The initial price tag can be
high. Another trap, the Mosquito MagnetTM, sells for as much as $1300. And this
is only for the initial trap and supplies. It does not include the cost of
replacing propane, attractants, or inhibitors.
In the war on mosquitoes, we are always looking for the ultimate product to
protect us from their bites. But if it sounds too good to be true, it probably
is. In the end, personal protection, including long-sleeved shirts and long
pants, insect repellents, and avoiding times of high mosquito numbers (dawn and
dusk) are proven, effective control measures. Better yet, these methods are far
less expensive than hi-tech traps.
Another typically, atypical summer! It's hard to believe it's August already. The state fair will be starting in three weeks.
katydid and bee.
Some good news is Deb Brown is well enough to be back in the Yard & Garden Clinic back to almost her usual schedule. Yes, she will be on Midmorning on MPR on Friday, August 2, at 10 a.m.
Our loss: Jon Powell, the Extension Service's turfgrass pathologist is leaving. Jon's moving back to Michigan. We will miss Jon. He's just a great guy, a capable and amenable colleague, and an enthusiastic educator. We hate to see Jon go but we sincerely wish him all the best!
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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