Yard & Garden Line News
Volume 5 Number 8                                                               June 1, 2003
Features this issue:
 Landscape Design Students Renovate the Display and Trial Garden
Why Lilacs Don't Bloom
Insolent Insolibasidium
Counting the Losses
Ash Plant Bug Common in Spring
Editorial Notes


Landscape Design Students Renovate the Display and Trial Garden
Julie Weisenhorn, Teaching Specialist - Landscape Design
Brad Pedersen, Professor, Horticultural Science-Landscape Design

Brad Pedersen explains technique. Eric Frisch rakes smooth soil for planting around new paver patio.
Exciting changes are taking place in the University of Minnesota Department of Horticultural Science Display and Trial Garden! The University will host the 2003 Minnesota Nursery and Landscape Association Summer Field Day on August 7th with the Display and Trial Garden scheduled as one the tours.

With the help of design students, staff and volunteers, this year's projects will provide a new and interesting focus for visits from Green Industry professionals involved in landscape design and implementation, plant production, turf management, and nursery and greenhouse management.

University of Minnesota landscape design students who are enrolled in HORT 5021 Landscape Design, Implementation and Management II traditionally work on a series of outdoor labs where they implement various landscaping projects on campus. This spring, the 30 students focused on a section of the Department of Horticultural Science Display and Trial Garden called the "Use Garden". In this area, plants not only have value as good landscape choices, but also have secondary uses such as culinary herbs, insect or mammal repellents, wildlife food / cover, medicinal uses, etc.

Andre Peterka and  Kurt Huiras use pavers to create new walkway.
The Use Garden, one of ten projects designed by this semester's class, was designed by a three member student team. The new design was implemented in 16 hours during the outdoor laboratory portion of the class. Students were fortunate to have UMN alumni Jim Peloquin of Premier Landscape, Inc. as this year's visiting landscape contractor. Visiting contractors not only bring their expertise and equipment to the project, but also demonstrate to students safe and proper methods of landscape implementation. With Jim's help and guidance, students installed a Victorian circle paver patio and serpentine walkway, berms and boulder walls, and an herb spiral. Eight pallets of pavers were generously donated to the project by Interlock Concrete Products, Inc., of Jordan, MN. Additional projects included re-working and improving mulched pathways, raising soil levels, repairing block walls, and dividing and transplanting the ornamental grass collection.

Located on the UMN St. Paul campus north of Alderman Hall, the Display and Trial Garden is managed by faculty and staff of the Department of Horticultural Science. It is the site of over 500 annual and perennial trials each year, and it is utilized as an outdoor laboratory by many departments and classes offered through the College of Agriculture, Food and Environmental Sciences. To learn more about the Display and Trial Garden, visit the Sustainable Urban Landscape Informations Series website, SULIS, at http://www.sustland.umn.edu
For a map to Alderman Hall: http://onestop.umn.edu/Maps/AlderH/index.html

Why Lilacs Don't Bloom
Deborah Brown, Extension Horticulturist

White lilacs in full sun at Mn. Landscape Arb. Photo credit: Deb Brown
Every year the Yard & Garden Clinice gets calls from people who are disappointed their lilacs only bloomed only sparsely or not at all, even though there were gorgeous lilacs blooming all over town – even in alleyways and in yards that look totally uncared for. Here's a rundown of the most common reasons a lilac might not bloom:

* Shade: Excess shade is the most likely culprit when lilacs fail to bloom well. Lilacs bloom best in full sunlight, or at least a half day sun. Anything less will mean fewer flowers developing. When they're in a location that's shaded all day, lilacs rarely bloom at all. Sometimes the shade creeps up over the years as nearby shade trees grow taller and fuller. In many cases, the lilacs may have been planted in a poor location to begin with.

* Pruning: If you prune lilacs back drastically, it may take a number of years before they begin to bloom again. They should produce flowers eventually, but it could take three or four years – maybe even longer.

If you prune only lightly, but wait until mid- to late summer to do it, you may not see many flowers the following year. That's because the flower buds for the following year are set shortly after the plant is through blooming. So if you do plan to prune, be sure to do it right after the flowers fade in spring. At the very least, you may wish to remove the brown flower/seed clusters which are unsightly.

'Miss Canada' blooms on west side of house. Photo credit: Deb Brown
* Nutrients: Lilacs are not heavy feeders; they don't need fertilizer to make them bloom. Often, in an attempt to help young plants become established, people will fertilize them several times each spring and summer. Plus, there's usually some lawn nearby, which is also fertilized. This abundance of nutrients, especially nitrogen, encourages the lilac to make a lot of leafy, vegetative growth – which may come at the expense of flower bud development.

If this appears to be the case, and the plant receives plenty of sunlight and hasn't been pruned too heavily or at the wrong time, simply stop the fertilizing. Eventually, it should begin to bloom well.

* Moisture: Lilacs grow best in well-drained soil. While wet, poorly-drained soil isn't directly associated with lack of blooms, it is associated with plants that develop root roots or generally fail to thrive. If you have a young lilac in a low lying moist location, transplant it to a more favorable site if at all possible.

Insolent Insolibasidium
Janna Beckerman, Extension Plant Pathologist

Leaf blight symptoms. Photo credit: Janna Beckerman
Honeysuckle (Lonicera spp.) is an increasingly popular and often used plant used in the home landscapes. Honeysuckles provide summer long flowers that are beloved of hummingbirds, beautiful blue-green foliage and the ability to thrive in full sun to part shade. However, like most plants, it has some rather serious diseases. One of the most serious diseases affecting honeysuckle is leaf blight. The causal organism is Insolibasidium deformans (formerly Herpobasidium deformans). Although the host range is limited to the honeysuckle family, most species and varieties of honeysuckle are susceptible to this disease.

Symptoms: Symptoms first appear on young, newly emerging foliage. Although infected areas are initially slightly crinkled or rolled, some cultivars ('Goldflame,' 'Dropmore Scarlet' and 'Mandarin') do not exhibit these symptoms. In some instances, chlorosis (yellowing) appears beginning at the veins and spreading outwards. The affected area later turns brown. Under cool, wet weather, lesions enlarge and coalesce. A zone of yellow tissue surrounds the affected area and large veins may remain green while interveinal tissue becomes necrotic (Fig. 1). Large leaf areas may become affected, or leaves can drop off with only what appears to be small lesions. This disease is commonly misdiagnosed as shoot blight because all the leaves on a given shoot can become affected. It is important to make certain that the woody tissue is not infected. Premature defoliation throughout the plant can occur with heavily infected leaves.

Signs: Although difficult to find, a thin white layer of fungal growth may be observed on the lower surface of infected leaves, and may resemble powdery mildew. Because honeysuckle is susceptible to powdery mildew, carefully check to make sure that no black fruiting bodies (cleistothecia) are visible.

Management: Because the fungus overwinters as mycelium and/or basidiospores in dead leaves, sanitation is a cornerstone of good disease management. Be sure to remove and dispose of infected leaves. Adequate plant spacing provides good air movement, allowing leaves to dry and reducing the risk of infection. If you are watering your plants, keep the water on the roots, and try to keep foliage dry.

The primary inoculum is the basidiospores. Basidiospores are released in the spring during periods of high humidity. The most severe infection occurs on young leaves (less than 20 days old) during temperatures of 59-64°F and high relative humidity (near 100%). As the weather warms and leaves harden off, infection rates decrease. However, the fungus continues to sporulate throughout the growing season during and after rainy periods.

If defoliation is recurrent and severe, fungicide use is warranted. Mancozeb (Fore) is labeled for control of leaf blight, listed as Herpobasidium blight.

Research has shown, and a quick walk through the woods will confirm that Lonicera dioica (wild honeysuckle) is resistant to this problem. Other resistant honeysuckles include: Lonicera gracilipes, Lonicera sempervirens (trumpet honeysuckle), and Lonicera japonica (Japanese honeysuckle) cv. 'Halliana.' It is important to note however, that Lonicera sempervirens and cultivar 'Halliana' have been found to be susceptible in other locations.

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

Counting the Losses
Beth Jarvis, Yard & Garden Line

Smokebush, in happier days. Photo credit: Beth Jarvis
The Master Gardener list serve is abuzz this spring with reports from Master Gardeners all over the state on what plants made it through the winter and which did not. A quick scan of the topics in the Ask A Master Gardener web board confirms that many plants are slow, dead or missing.

Many trees, notably catalpa, have been very slow to leaf out. Honeylocust have also been a concern. Smokebush (Cotinus) appear to be hard hit with many totally dead but some with only lower branches leafing out. Redbuds range from wonderful blooms to "deadbuds", all within the Twin Cities.

Shrub roses suffered more than normal. A number of ornamental grasses also appear to have failed . Marginally hardy grasses that survived the last few winters are goners this year. And, many gardeners are patiently checking the bases of hardy hibiscus, normally a slow starter, to see if they're coming back.

A few groundcovers, particularly ajuga, seems to have been slow. Ajuga is normally considered a bit marginal for zone 4. However, creeping Charlie appears to be hale and hearty!!

Ash Plant Bug Common in Spring
Jeff Hahn, Assistant Extension Entomologist

Ash  plant bug feeding. Photo credits: Jeff Hahn
Green ash is host to a common insect, the ash plant bug. They overwinter as eggs and emerge in May as small (1/16 inch long) nymphs. They later mature into 1/4 inch long, oval, brown and yellow adults. Ash plant bugs are often not noticed because they move quickly and feed on the underside of leaves. They have two generations and are active throughout the summer.

Both the nymphs and adults feed on plant sap in the leaves with needle-like mouthparts. This results in a yellowish or whitish pinprick or speckled discoloration that appears on the upper surface of the foliage. You may also find tiny, black dots of excrement on the bottom of leaves. When feeding is heavy, these damaged sections can coalesce into brown areas. Although these insects feed all summer, this damage is most severe in the spring when leaves are young and tender.

This feeding injury is primarily aesthetic, just affecting the tree's appearance. There is rarely any lasting damage inflicted on ash, especially if they are healthy and well-established plants. It is possible for very young or very stressed trees that are heavily infested to be injured by ash plant bugs.

Ash will sometimes drop leaves prematurely in spring. Although ash plant bugs may be present, they are not the likely culprit of this leaf drop. It is often the result of ash anthracnose, a disease. Ash anthracose usually exhibits brown, irregularly shaped spots, although sometimes this is not very apparent. In some cases when disease is not the cause, ash leaves can fall prematurely from unusual early season weather conditions.

Treatment of ash plant bug is rarely necessary to protect tree health. Just tolerate and ignore them. In cases where young or stressed trees are at risk, apply a residual insecticide labeled for ash, e.g. permethrin as soon as damage is noticed in May.

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm


Editorial Notes

Bridalwreath spirea
Photo credit: Beth Jarvis
A neighbor's bridalwreath spirea hedge is in bloom right now and it's quite lovely. (It's not the one in photo.) The long arching branches remind me a bit of buddleias.

Over the last few years we've seen more buddleas in Minnesota gardens. Next issue, we'll find out how buddleia fared when raised on the U's St. Paul campus. Jeff Gillman, Nursery Edxtension, will share his insight into which ones you might want to try to grow and which ones just won't work..

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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