|Yard & Garden Line News
Volume 5 Number 9 June 15, 2003
Some Notes on Buddleia
Jeff Gillman, Extension Nursery Management Specialist
Buddleia davidii, more commonly known as butterfly-bush, is known as one of greatest butterfly attracting plants in the nursery industry today. Minnesota, however, does not have a climate that readily lends itself to buddleias' need for warm winters.
'Royal Red' rarely survives winter here.
Over the past few years, the Teaching Research Extension (TRE) nursery at the University of Minnesota has trialed a few buddleia cultivars to establish whether any of them could tolerate Minnesota winters. What we have established is that, indeed, there are no reliably root-hardy Buddleia davidii cultivars for us. Despite this lack of hardiness, there are a few cultivars out there that are worth looking at because they have a chance to live as a perennial for a number of years (until a particularly bad winter). A few cultivars should be avoided because they simply can't make it through even our mildest winters.
The first rule of thumb is that the most common cultivars out there are not going to survive the winter. 'Royal Red' and 'Black Knight' rarely make it through a Minnesota winter without heavy mulching. Additionally, the yellow cultivars including 'Honeycomb' and 'Sungold' are B. davidii crosses with the South American buddleia species B. globosa and their survival, as anything but an annual, is highly in doubt.
Some of the cultivars that we (and others) have brought through a winter as perennials include 'Mary's White' which survived two winters for us, with no mulching, until this past winter and 'Rice Creek' which was selected by Betty Ann Adison and Harvey Buchite of Rice Creek Gardens.
Additionally we are trialing a new seedling buddlia that we discovered growing as an escape in one of our containers at the end of the winter two years ago. This plant will be trialed for at least two years before it is released for production. There is another species, B. alternifolia, that is significantly more cold hardy than B. davidii and might survive here. This species is extremely attractive and I have seen it trained into a tree which would be very difficult to do with B. davidii. We have not trialed this species because it has one major drawback -- it blooms only once a year on old wood and so butterflies are only attracted into the garden for a portion of the season.
The cultivars listed as more cold hardy have a slightly better than fair chance of surviving the winter without mulching, but for best success be sure to mulch your plants over the winter months.
If you think that you'd like to try growing buddleia there are just a few concerns, besides cold hardiness, that you need to worry about. Buddleias, in general, are best sited where they can be allowed to grow freely and show off their wild and
wooly form while bringing in all of those summer butterflies like skippers, sulfurs, and especially swallowtails. It is widely thought that these plants needs sun and, for maximum flowering, that is absolutely true. However, these plants will survive in the shade but will be even leggier than usual and won't produce as many blooms.
Butterfly-bush with butterfly.|
Buddleia can handle a wide range of soil textures and pH levels. One of buddleia's great claims to fame is that after World War II it was one of only two woody species that would live and grow in bombed out buildings. Buddleia does prefer well drained soil, but it can handle slightly wet soil. Additionally, while buddleia does prefer a slightly acid pH, it can handle alkaline conditions and often thrives at a pH above 7 or even 7.5.
Much of the literature lists butterfly-bush as drought tolerant, and indeed it is, but when this plant is placed into overly dry conditions it is one of the ugliest plants that you would ever care to see. Dry conditions cause wilt to an extent not seen in many other plants and it develops insect and disease problems (something it normally does not do). Buddleia can be pruned extensively without much damage, however, the only recommended pruning technique is to cut this plant back to a point slightly above the soil line every winter as the growth above this zone is likely to die during the winter anyway.
Is It an Emerald Ash Borer?
Jeff Hahn, Assistant Extension Entomologist
Emerald ash borer is an exotic beetle that was found in the U.S. for the first time last year (see Yard and Garden News, April 1, 2003, http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Apr0103.html#emerald). It currently has been detected in Michigan and Ohio. It has also been found in Canada in Windsor. So far it has not been discovered in Minnesota, although it may be just a matter of time before it is. Once it is found here, every possible step will be taken to eradicate them from the landscape.
Emerald ash borer|
Photo credits: USDA Forest Service
There are two ways to recognize the presence of emerald ash borer. The first would be finding symptoms in ash. These could include unexplained or sudden dieback in ash. Close inspection could reveal 1/8 inch ‘D' - shaped exit holes in the trunk and branches as well as criss crossing larval tunnels under the bark.
You may also see an emerald ash borer adult in the landscape. Emerald ash borer is a coppery green color, about 1/3 - 1/2 inch long and bullet shaped. It is widest just behind he head, tapering back to the abdomen. Because this beetle flies, it could be found almost anywhere in a yard. Adult emerald ash borers are active from late May to late June.
But be careful as there is at least one native insect that could fool you into thinking you have seen an emerald ash borer. The six-spotted tiger beetle is also an iridescent green color. Although at first they appear similar, when placed side by side, it is clear that they are different insects.
Photo credits: Jeff Hahn
Tiger beetles are a similar size, about 3/8 - ˝ inch long. They have a conspicuous head with eyes bulging on the sides. The prothorax (the first segment of the thorax, right behind the head) is distinct and a little narrower than the head. The abdomen and rest of the thorax is wider than the head or prothorax. Watch for six white spots (three on each side) on the margins of their wing covers, although sometimes they are hard to see. Tiger beetles are typically found on the ground. They are predators and run quickly. When alarmed they will rapidly fly a short distance away and then land. Tiger beetles are first out in May and are active throughout the summer.
If you do find a beetle you believe is an emerald ash borer, try to catch it and have it identified. Also, If you encounter any ash that have unexplained dieback or other symptoms of emerald ash borer or has mysteriously died recently, call the Minnesota Department of Agriculture's Arrest the Pests Hotline at 651-296-MOTH (6684) or 1-888–545-MOTH (6684) to report it.
Click Beetles, an Occasional Nuisance in Home
Jeff Hahn, Assistant Extension Entomologist
June is a common time to find an occasional click beetle in your home. Many click beetles are brown, relatively slender, and about ˝ inch long. The larvae feed on the roots of various plants, including corn, small grains, grasses, and potatoes and other root crops. Adults are found on the leaves of trees and shrubs.
Photo credits: Jeff Hahn
Click beetles get their name because of their ability to right themselves if they are upside down on their back. They arch their back, then snap it forward which throws them up into the air. There is an audible `click' through this action. It may take more than once, but the beetle eventually is able to get back right side up.
These beetles can be drawn to homes because they are attracted to light. They are also attracted to moisture, e.g. a clogged gutter. Click beetles can get inside by move through small cracks or spaces. Once inside, click beetles are commonly found on walls and ceilings.
Click beetles are harmless to people and property. Once indoors they are short-lived, lasting a few days. They are a temporary nuisance, entering homes for about three to four weeks during summer. Physical removal is the only necessary control. You can reduce attracting them if large numbers are encountered by keeping unnecessary lights off at night or removing obvious sources of moisture.
Friendly Flies: Good News, Bad News
Jeff Hahn, Assistant Extension Entomologist
The good news is that forest tent caterpillar numbers in the state are finally dropping significantly. The DNR reports that populations have dramatically decreased in many areas and all that remains are occasional pockets scattered throughout the northern area of the state. Known areas of forest tent caterpillar include a band in Itasca county extending from Deer River to Grand Rapids through the Iron Range and up to Virginia and isolated pockets around Gooseberry Falls state park and Cloquet. They are also found in scattered sites from Grand Rapids to Cass Lake, around Bemidji and southern Clearwater county.
Very friendly flies.
Photo credit: Jeff Hahn
A significant reason for the decline of forest tent caterpillars is the parasitism of Arachnidomyia aldrichi, better known as the friendly fly. This is a medium-sized insect, 3/8th - 7/16th inch long, with red eyes, a grayish body, three black stripes on their thorax, and a checkered abdomen.
Starting in mid June, these flies emerge from pupae in the ground and seek out forest tent caterpillar cocoons. The flies deposit live larvae (maggots) on the outside of forest tent caterpillar pupae. These young maggots bore into cocoons and feed on the pupating insects, thus killing them. Eventually the maggots drop to the ground to pupate where remain until next June.
As forest tent caterpillar numbers start declining, friendly fly populations dramatically increase. The bad news is that friendly flies will be almost as abundant as the caterpillars themselves. The good news is that friendly flies are harmless to people. They don't bite, sting or transmit disease. However, the bad news is they a nuisance and can be quite annoying.
They have the irritating habit of landing on all kinds of surfaces, including homes, cars, laundry, and people! These surfaces can become stained from their droppings. Friendly flies seem to be especially attracted to light colored surfaces and to sweat (salt). They get their name friendly fly because they are difficult to discourage or brush away. You knock one away from you and it usually flies right back to where it had been resting.
Friendly fly adult
Photo credit: Jeff Hahn
Friendly flies have been occasionally referred to as government flies because of the mistaken belief that a state agency deliberately released this fly into Minnesota to combat forest tent caterpillars. However, like forest tent caterpillars, friendly flies are native to this state.
It is very frustrating dealing with large numbers of friendly flies. Unfortunately there are few options for coping with them. It is ultimately a matter of tolerating them until they go away on their own. The good news is they will be active only until mid to late July. Keep in mind that however much we do not like these insects, they are hugely responsible for forest tent caterpillar numbers collapsing which is insect we like even less.
Get the low down on this month's insect pests at
Watch for new ‘Endless Summer' Hydrangea
Deborah Brown, Extension Horticulturist
Minnesota gardeners always dream of growing plants that aren't quite hardy here. High on the list are flowering dogwoods, Japanese maples, and blue hydrangeas. Katherine Lanpher, host of Minnesota Public Radio's Mid-morning Show, calls this overwhelming desire "zone envy."
Growing in acidic|
Photo credit: Bailey Nurseries
To my knowledge, no one is working to create a "northern" flowering dogwood, and while there have been reports of a few successes growing Japanese maples in extremely protected sites, the only plant of the three that looks as though it has a bright future here is blue hydrangea.
Blue hydrangeas, are members of a group called "big-leaf hydrangeas," Hydrangea macrophylla. Though their stems are somewhat hardy here, their flower buds usually are not. Since the flower buds for one year are developed the summer before, those buds must survive our winters in order to produce flowers the following year. Even with good winter protection, this is no mean feat!
Every year we hear from people who planted ‘Nikko Blue' hydrangeas only to find they bloomed well the first summer, then looked green and healthy the following summer – but they just never bloomed again. While their leaves are attractive, if somewhat coarse, it's doubtful anyone would plant these hydrangeas exclusively for their foliage. They want those showy large "balls" of sky blue flowers.
Well, help is on the way. Bailey's Wholesale Nurseries is introducing a big-leaf hydrangea that produces its flower buds on new growth that develops in spring. That means even when the stems die back severely, as they might following a difficult winter such as we had this past year, the plants will still go on to produce flower buds that will bloom the same summer. Appropriate throughout USDA climate zone 4, the plant has been named ‘Endless Summer.'
Growing in alkaline soil. |
Photo credit: Bailey Nurseries
Limited numbers of the plants will be in nurseries and garden centers this summer. By 2004, however, they should be much more plentiful. You might even want to put in an order with your local nursery or garden center – especially if you've always longed for an exotic-looking blue hydrangea.
Like other big-leaf hydrangeas, the flower color of ‘Endless Summer' is dependent on the pH of the soil the plant grows in. To produce blue flowers, you must acidify the soil and continue to keep it quite acidic. If your soil is alkaline (as are most soils in the Twin Cities and much of greater Minnesota) but you don't want to monkey around acidifying it, the flowers will open a lovely clear pink.
Keep in mind, this is primarily a "heads up" so you can keep an eye open for this plant. Other big-leaf hydrangeas simply won't perform as well in our climate.
Frustrating Foliar Fungi
Janna Beckerman, Extension Plant Pathologist
The return of the swallows to Capistrano is considered a harbinger of spring. In Minnesota, a sure sign that spring is here are the calls to the Yard and Garden Clinic by alarmed tree owners, beginning with ash tree owners. This year, due to a cool spring and unusually wet weather, our steady supply of clients has turned into a deluge. In addition to ash, ornamental crabapple, maple and oak owners are joining the fray. Frantic phone calls are followed by the arrival of deformed, blighted and wrinkled leaves. The homeowners are focused on their trees, and their problems are often easily reduced to two questions: "What is wrong my tree?" and "What do I spray?"
Minnesota spring commonly begins with ash anthracnose.
Foliar diseases of ornamental trees are frustrating problems. The frustration isn't due to the disease, but more often than not, the expectation of the homeowner who has little to no tolerance for the pathogen causing the disease! Leaves are one of the most visible features of a tree, and people quickly notice any change in appearance. Homeowners may notice as little as five percent defoliation, and ten-percent defoliation may send some owners into a panic. What is most unfortunate is that of all tree diseases, foliar diseases are usually the least life-threatening. Otherwise healthy trees can tolerate several seasons of partial defoliation without suffering significant injury. In fact, trees produce such an abundance of leaves, that some loss of foliage is not a major cause for concern. As long as the tree regularly maintains two-thirds of its canopy, there shouldn't be a cause for alarm. Convincing the homeowner of this is another story, more fittingly told by a plant psychologist as opposed to a plant pathologist!
All joking aside, it needs to be stressed that the loss of many leaves early in the growing season can result in depletion of food reserves as the tree attempts to re-foliate. If this defoliation is repeated for several years, the tree may become vulnerable to attack by secondary pathogens and/or opportunistic insects. This vulnerability results when the tree depletes its carbohydrate reserve and then lacks the energy to defend itself. Normally trivial problems can become catastrophic to these predisposed trees. Thankfully, recurrent defoliation that results in almost total leaf loss is an unusual occurrence.
trees commonly re-foliate after infection by anthracnose.
And the reason for this season's onslaught of fungal, foliar disease problems? Our cool, wet spring has created conditions that encourages the new, succulent growth to continue to grow, and prevents this growth from maturing and becoming easily infected. This phenomenon is coupled with environmental conditions that favor the repeated sporulation of numerous fungi that cause foliar disease, and leaf drop as well. Below is a list of the most common foliar diseases we've seen this year, and links to provide you with more information on their diagnosis and management.
Ash Anthracnose http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p413ashanthrac.html
Apple Scab http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p220applescab.html
Dothisroma Needle Blight http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/P424dothistroma.html
Honeysuckle leaf blight http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June0103.html#insolent
Maple Anthracnose http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June1502.html#maple
Taphrina of Maple
Alternaria leaf spot on apple/Crabapple
At a stoplight this morning, I glanced at the car beside me and noticed weigela blooms in the passenger seat of the next car. It might have been a shrub in a pot or someone brightening the workplace with a bouquet. Weigela are popping up everywhere! My brother and sister-in-law have one growing in their Duluth yard. People stop and ask the name of the shrub.
It's Weigela florida with cultivars ranging in size from a couple of feet to six feet and corresponding spread. Shades of pink and red are most common, but CarnavalTM weigelia, which is W. floridus 'Courtalor' boasts blossoms in red, pink and white. Weigela foliage ranges from variegated green and white to purple. These shrubs are hardy to zone 4.
In an upcoming issues, you'll hear about the Master of Ag program at the U. You'll also get to meet Dr. Tim Kurtti, who does deer tick research. And, my friend and colleague Cindy Tong, who is a post harvest physiologist, and I will visit the St. Paul Farmers' Market in search of exotic Asian edibles. We will attempt to identify and demystify the veggies you might use if you knew what they were! Some time way off, we'll be hearing about the progress on developing hardy Japanese maples for Minnesota.
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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