Cotoneaster – Renovating an Old Hedge

Cutting back the old hedge to 6" above grade

Ready to grow!

A perfectly trimmed cotoneaster hedge can be a great addition to an ornamental landscape in Alberta. Over the years, however, many hedges become overgrown, too big to manage, or infested with insect or disease problems. When this occurs, it may be time for a drastic renovation to ground level.

In recent years, scale insects have ravaged cotoneaster hedges. In Calgary, the pest is oystershell scale; in Edmonton, it is mainly scurfy scale. From my experience, I would say that oystershell scale is more serious, but both insects eventually take their toll on the hedge, by leaving dead, patchy areas in the canopy. Uncontrolled, the insects will kill the hedge. With a regimen of drastic renovation, combined with properly times insecticidal sprays, scale insects can be controlled, and your hedge can cotinue to look great.

Renovation is a dirty, dusty job, but is very straightforward.  Begin at the end of the hedge, and cut all stems to about 6″ above ground level.  Remove dead stems, leaving only fresh, healthy stubs.  New growth will occur from the cut ends, and also from new suckering growth from the exisiting root system.

If your hedge was infested with scale insects, be sure to treat the stumps with a contact insecticide around mid-June, when the immature scale insects are crawling.  New, healthy stems should reach a height of about 2′ the first season.  Hedge training may being as early as the second season after renovation.

For more information on hedge renovation, please call Wild Rose Tree Service at (403) 755-2443.

(c) Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB

Repairing Winter-Damaged Cedars

Getting started

Finished product

 Unsightly cedars are a pretty common sight this spring, thanks to many snowfalls throughout the winter. But don’t despair, because they can be repaired.

 

The example below is in south Edmonton. The snow loaded down the branches on this tree so much that the owners had a hard time getting in and out of their front door.

 

The first thing I had to do with this tree was to tie back all the wayward branches, in order to restore its true form. I accomplished this using 3′ long snap-ties.

 

Once I had the tree looking more presentable, I started the shearing process to give it a more ornamental shape. When shaping cedar, it is best to use a good, sharp pair of long-handled hedging shears, not power trimmers. Hand shears give a much cleaner cut, which prevent browning of the cut ends later on. It is best to start the shape at the top of the tree, and work toward the base. I always make sure to trim around the eavestroughs, and trim for clearance off the house.

 

The final product looks a bit more appealing. Routinely sheared cedars will resist further storm damage, as shearing reduces the end weight on the branches, and encourages lateral growth, making a thicker, fuller canopy.

 

(c) 2011 Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB, (403) 755-2443

Dogwood (Cornus spp.)

Dogwood is truly one of the most reliable garden shrubs for Alberta.  Native to parkland forest understories, it is also one of the only plants that will grow well in shady areas of the yard.  I consider dogwoods a four season ornamental, with interesting flowers in the spring, nice berries in the summer, great fall colour, and beautiful bright stems to provide winter interest.

There are many cultivars of dogwood available at nurseries.  Personally, I prefer the species, Cornus stolonifera, as it is most hardy.  That being said, all of those rated zone 3 or less should work fine, provided they are planted and maintained properly.

Red-Osier Dogwood (Cornus stolonifera)

Red-Osier Dogwood near Sylvan Lake, AB. Shane LePage photo.

This species is my favourite dogwood.  One of its best assets is that it will grow well in shadier sites, which is common in mature Alberta neighbourhoods that are clustered with shade-throwing spruce trees.  In Red Deer,  I often recommend dogwood or cedar for less-than-ideal light conditions.

Lately, I’ve taken an interest in Niwaki, the japanese art of pruning, and am experimenting with some mature dogwood plants in Red Deer.  Given enough space, dogwoods need little pruning.  But if it’s a dramatic display of bright new stems, or if the shrubs are included in a dense, mixed planting, where spacing is not desired, pruning is a definite must.  Also, old, overgrown dogwoods tend to benefit from reinvigoration, every few years.

Pruning to Encourage Decorative Stems

This technique is most suitable once the specimen has an established root system.  I don’t recommend the following technique on newly planted shrubs.  In late winter to early spring, cut back all dogwood stems to about 4″ above ground level to form a tidy “stool.”  Don’t be alarmed if the plant doesn’t respond with new growth early in the growing season.  In the Red Deer area, I find that it takes well into July to get a nice looking, regenerated shrub.  It is worth the wait.  The new foliage seems to glow with vigour and rich, healthy colour.  This process can be done annually, but I find that it’s a nice idea to rotate this type of hard pruning between various dogwoods in the garden, alternating years, or perhaps pruning this way every three years, or until they start to encroach on neighbouring plants.  All dogwood cultivars can be pruned similarly.  Yellow-twig dogwood is particularly suited to this technique.

Reinvigoration of Overgrown Specimens

Most often, I am called in to look at messy, overgrown specimens dominating some corner of a back yard.  I prefer to prune dogwood in the dormant season, late fall to early spring, so I can see what I’m working with.  I remove as much deadwood as is necessary for the specimen, but usually dead stems down to 1/8″ diameter or smaller.  The shrub should look neat and clean, for starters.  Next, I remove conflicting stems; those that intertwine, saving those that best contribute to the overall form of the shrub.  I like all remaining stems to have a bit of space, especially if it will be several years before the shrub is pruned again.  Lastly, I reduce the height and width, only as much as necessary, and using reduction-type pruning cuts, in order to balance and contain the shrub.  The end result is a tidy, attractive, balanced, and healthy looking specimen.

Irrigation & Fertilization

As with most woody plants, dogwoods prefer a moist, well-drained soil, with a wood-chip mulch cover.  Planted and maintained in this manner, these plants should not require irrigation or fertilization.  I would consider watering only after prolonged hot, dry weather in summer.

Pests

Dogwood is insect and disease resistant.  I have, however, encountered some problems, namely aphids and oystershell scale.  Aphids are messy and unattractive, buy they aren’t that serious.  Hose them off of try some relatively non-toxic spray, such as an insecticidal soap.  Other contact insecticides work well, such as Malathion, but please use caution when using chemicals.  Oystershell scale is more serious, and must be controlled when the scale “crawlers” are active, in early to mid-June.  Use any contact insecticide.  In my practice, I have used Orthene with excellent success and it offers systemic control as well.  Timing is everything.

(c) Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB, (403) 755-5899

Oystershell Scale

Of all the pests that I work with in Calgary and Red Deer, the scale insects are doing the most damage.  And while European Elm Scale is now familiar to homeowners and tree professionals, oystershell scale is largely unknown to people, and its potential for damage grossly underestimated by arborists and landscapers.  It attacks 120 species of ornamental trees and shrubs, many of which are commonly planted on the Prairies.  Without proper recognition, this pest will destroy countless plant materials in Alberta.

Oystershell scale on cotoneaster twig. Biterroot Restoration photo.

 A fellow arborist first called my attention to oystershell scale in Calgary in 2006.  He had a number of clients in the Inglewood neighbourhood, with dying cotoneaster hedges.  We didn’t know what it was at that time.  I looked at the hedges, took a sample, and soon identified it.  Since then, oystershell has spread throughout the city, particularly severe in some neighbourhoods, such as Riverview and Douglasdale, and just getting started in others, such as Acadia, Lake Bonavista, and Britannia.  Cotoneaster is the preferred host, but we have now seen it infesting common lilac, crabapples, edible apples, hawthorn, and green ash trees.  Entire streets have lost their cotoneaster hedges in at least one southeast neighbourhood.

Identification

Infested cotoneaster hedges die-back in patches, leaving large voids in the hedge.  Close inspection of the twigs reveals thousands of adult oyster-shaped insects encrusting the stems.  In early to mid June, if an infestation is not obvious, take a piece of black paper or similar sized piece of black leather (I use a leather folder), and shake the branches over it.  Look closely.  If scale is present, you will see many tiny orange or reddish “crawlers”, which is the immature stage of the insect.  A few crawlers might not warrant control measures.  A heavy infestation will require a spray.

Pest Control

Oystershell scale insects are easy to control.  They appear to have one generation per season in Calgary.  The crawler form is active in early to mid June, depending on weather conditions.  Inspect the leaves as described above.  If the infestation level is moderate to high, you can spray the entire canopy, thoroughly, with any contact insecticide.  I recommend hiring a licensed pesticide applicator, as they have an arsenal of different chemicals, as well as appropriate spray and safety equipment.  I have successfully used permethrin, malathion, and acephate to control these pests.  I prefer acephate as it gives systemic control for up to several weeks, should my timing be off slightly.  Dormant oils in late winter, before bud break, may offer control as well, although I haven’t used this method .  Spray all other infested trees in the same manner.

Renovation of Infested Hedges 

Heavily infested, or patchy hedges, are unsightly and will never recover as well as homeowners would like.  In this case, the best thing to do is 1) cut the hedge back to about 8″ above grade in late winter, before bud-break.  You may get away with cutting back sections of the hedge only; 2) in June, spray the sprouting stumps with a contact insecticide (oystershell will attack stems right to the base of the plant); and 3) as your new hedge grows, monitor pest populations in early June and spray with a contact insecticide, if necessary.  Through careful monitoring and appropriate spray treatments, this insect is easily controlled.  Exception:  If you hedge is “nearly-dead” or devoid of vigour, you would best remove, grind the stumps, and replace the plants.

For further information, please call Shane at Wild Rose Tree Service at (403) 770-2974.

(c) 2011, Wild Rose Tree Service & Pest Control, Red Deer, AB

Cottony Ash Psyllid

For information on the biology and control of this pest, please refer to the following link to the City of Red Deer Fact Sheet:

http://www.reddeer.ca/NR/rdonlyres/B8D5D6D6-6F39-4F6B-A98D-BFBB419AFB17/0/Feb2008CottonyPsyllidhandoutRPC.pdf

Red Deer Experience

This pest has been tough to control.  Most trees in Red Deer in 2009 were in decline or nearly dead.  In 2010, likely due to a cold, wet spring and early summer, pest populations appeared to be much lower and many trees appeared to be “bouncing back.”  Whatever 2011 brings, my long-term outlook for black and manchurian ash trees is not good.  Calgary has very few of these trees left, and no sensible arborist would recommend that any client plant a new one.  My feelings are the same.  I no longer recommend planting either species and encourage clients to plant one of the trees on my list of preferred, hardy trees.  Please see my post, Shane’s 10 Favourite Trees for Red Deer.

Control Measures

There are two generations per season for this insect.  Over the past two seasons, I have been injecting the trunks of infested trees, in the first week of June, with Confidor (imidacloprid).  So far, I’ve found that the chemical is keeping most of these trees alive, but that’s it.  Injected trees have not returned to a vigorous state.  I also have found that the chemical is only effective with established trees.  Confidor does not seem to control psyllid on newer trees, with poorly established root systems.  For these trees, I recommend removal.  For larger, established trees, I recommend chemical control, followed by pruning to remove the unsightly, dead branches.  We are likely fighting a losing battle with this pest, and unless you are prepared to spend some money to control the insects, I suggest you plant something else.

Shane’s 10 Favourite Trees for Red Deer

   (403) 755-5899 Red Deer  (780) 628-5835 Edmonton

Ponderosa pines at Bow Point Nursery. Ken Wright photo.

 Not all trees species are created equally when it comes to Red Deer weather and growing conditions.  The following is a list of my favourites.  They are tough, hardy, insect and disease resistant, and great trees to have in the landscape.  And while I can’t guarantee these will grow well for you, they represent some of the best bets in the Red Deer area.

1.  Scots Pine (Pinus sylvestris) – My favourite tree and official pick for 2011.  Hardy, maintenance free, likes full sun, interesting orange bark.  Great natural form.

2.  Trembling Aspen (Populus tremuloides) – You can’t get any tougher than this.  Healthy specimens are among the nicest compact shade trees.  They can withstand a myriad of insect and disease problems.

A walk in the aspens at Jarvis Bay with Baby Victoria

3.  Ussurian Pear (Pyrus ussuriensis) – Hardy, insect/disease resistant, nice white flowers, great form

4.  ‘Paskapoo’ Poplar (Populus balsamifera ‘Paskapoo’) – Very nice, compact shade tree for the smaller yard.  Supremely drought tolerant, insect and disease resistant.  Available at Bow Point Nursery in Calgary.

5.  Ponderosa Pine (Pinus ponderosa) – Hardy, maintenance free, likes full sun, beautiful form.

 

6.  Lodgepole Pine (Pinus contorta) – Our provincial tree.  How can you go wrong?

 

 

 7.  ‘Spring Snow’ Crabapple (Malus x ‘Spring Snow’) – This tree was introduced to the Prairies in the 1960’s and I just discovered it a few years ago.  Beautiful white flowers in the spring, but NO crabapples.  The flowers are sterile.  Great backyard tree without the mess of a typical crab.  You can buy this at one of the local nurseries in Red Deer but you’ll likely have to order it in the Spring.

8.  Pin Cherry (Prunus virginiana) – A tougher alternative to the mayday and ‘Schubert’ chokecherry.  Beautiful bark in winter.

9.  Bur Oak (Quercus macrocarpa) – Very long-lived but slow-growing; nice fall colour.

10.  Siberian Larch (Larix sibirica) – If you’ve got the space, this is a great tree.  Its very hardy, drought tolerant, insect & disease resistant, long-lived, and has excellent fall colour. 

'Pascapoo' in fall colour. Courtesy of Ken Wright, Bow Point Nursery

Honourable Mention:

Cedar/Arborvitae (Thuja occidentalis) –  I never paid much attention to this tree, thinking of it mainly as an overgrown shrub.  But I was wrong.  This is a great tree for Red Deer north, especially in the shadier areas where other trees are tougher to get started.  Hardy and long-lived.  I love it.

(c) 2011 Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB

Birch Leafminer

Birch leafminer damage on weeping birch, Red Deer, AB

This is a very common pest in the urban landscape in some areas.  In the summer of 2009, there was a serious epidemic in some Red Deer neighbourhoods, but populations declined greatly in 2010, most likely due to a cold, wet spring, and generally cool summer.

Birch leafminers are sawflies, jet-black, wasp-like insects that are about 3.5mm long with a 7mm wing span.  They overwinter as larvae in the soil and pupate in the spring.  Adults mate and begin egg laying, on the leaves, in mid-late May.  Larvae enter the leaves and feed on the inner leaf tissue, leaving the characteristic skeletonized, brown patchy leaf.  Last I heard, there are up to 5 different species of birch leafminers, with a potential for 9 generations per season!  That’s a lot of potential damage to your birch trees.

Leafminers won’t kill the birch tree.  Repeated attacks, year after year, will weaken the tree however, leaving it stressed and open to attack by other insects, such as bronze birch borer, a much more serious pest that will ultimately kill the tree, usually over the course of a few seasons.  Also, leafminer attacks leave the tree looking brown and sick, which hardly adds to the esthetic appeal of your yard.

Chemical Control

Systemic insecticides applied to the soil in late May will offer season long control of birch leafminer, aphids, and anything else that sucks or chews on birch leaves.  Last year, the best chemical, Lagon 480E, was taken away from pesticide applicators for residential use, due to its high toxicity and tendency to leach into groundwater.  The one systemic chemical still available for leafminer control is called Orthene.  Contact Wild Rose Tree Service for more information on spring application of Orthene and other pest control chemicals.

Biological Control

There are parasitic wasps that prey on leafminer insects, which may be helpful in keeping leafminer populations in check.

Keep your birch trees healthy.  Give them a good soak, throughout the dripline, during extended hot weather.  Don’t over-fertilize as this has been shown to exacerbate insect problems.

(c) 2010 Shane LePage, Wild Rose Tree Service, Red Deer, AB

Fire Blight

A common disease of crab apples and mountain ash trees in Alberta

Fire blight is very common on the Prairies.  Some years are worse than others.  In Calgary and Red Deer, in 2009, it was particularly severe.  Epidemics occur during warm, humid weather, with relative humidity above 60%.  The bacteria responsible for the disease can multiply at temperatures between 15-32C, but do so most readily between 27-29C.  Outbreaks can follow severe storms, where broken branches leave entry wounds for the bacteria.

Symptoms of fire blight can affect blossoms, fruiting spurs and twigs.  In Alberta, it is often too cold for fire blight to appear in the blossoms, and I usually see infected spur leaves (see picture) and cankers on twigs. 

Plants grown in moist, well-drained soil, with adequate nutrition, can best resist the disease.  Once infected, proper pruning will delay the spread of the disease.  Infected branches should be removed to about 8″ below the last sign of bacterial canker.  It is best to prune infected trees during the dormant season to limit the potential for disease spread.  Avoid pruning blight infected trees in summer or when conditions favour the disease.

I encounter fire blight most commonly among crab apples, mountain ash, and cotoneaster, although it occurs on many other species of trees and shrubs.  Severely infected hedges can be renovated (cut down to about 6″ above soil level) in late winter or early spring.  Badly infected trees should be removed and replaced.  Moderately infected trees should be pruned.

There are chemical controls for fireblight that are available from pest control professionals.  Control measures consists of spraying repeatedly with copper oxychloride and streptomycin, about every 10-14 days during the growing season.  Obviously, due to cost and environmental implications, I do not recommend chemical control measures, except on highly valuable landscape trees.  Replace badly infected trees with fire blight resistant plant varieties.

(c) 2011 Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB

Black Knot Fungus

Black knot in mayday at commercial lot in Red Deer. Shane LePage photo.

 Black knot is one of the most commonly encountered diseases among ornamental plantings.  I see it most often on mayday and ‘Schubert’ chokecherry trees.  Besides poor planting techniques and poor plant quality, black knot is the most common cause of plant death among those species.

Easily recognizable, black knot starts as swellings on the twigs in the fall, after being infected earlier in the spring.  These swelling often go unnoticed until they begin growing larger the following year.  When conditions are right, trees will often become infected year after year and require significant care and maintenance in order to remain healthy.

Pruning and sanitation are the preferred treatments.  I prune out all “knots” back to a lateral branch, making sure that I cut back at least 6″ from the bottom-most part of the “knot”.  You can see the brownish discolouration in the wood that results from the infection.  Keep cutting back until you no longer see the discolouration.  In trees that have a “systemic” infection, that won’t be possible unless you remove the entire tree, which is exactly what I do in severe cases.  Make sure all infected branches are removed from the property.  Ideally, cut branches should be buried or burned, but I have yet to see or hear of anyone who does this.  Tree services will chip the infected branches, which later become part of mulch or compost piles.  Many branches end up at a local dump and are either chipped or buried.

Through regular observation and pruning, this disease is easily controlled and, provided you planted the tree properly in a suitable site, you can have a healthy mayday or ‘Schubert’ for many years.  All too often, I am called in to prune an infected tree after the disease has spread beyond the point of complete control.  To make matters worse, many people do not follow through with regular maintenance, and the disease quickly recurs, and spreads to neighbouring trees.

I have seen mayday trees in commercial parking lots, like the Galaxy Cinemas on St. Albert Trail in Edmonton, that are so heavily infested with black knot, that they take on an ornamental appearance, perhaps similar to Christmas lights.  The trees in the surrounding neighbourhoods haven’t much of a chance with a breeding ground like this nearby.  Annual maintenance is critical.

Acreage owners and city dwellers that border natural areas should be warned that native chokecherries often harbour the black knot fungus.  The disease will easily spread from the forest to landscape trees.  Check your trees for black knot each season.

(c) 2011 Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB

Currants

Currants are quickly becoming some of my favourite shrubs.  They are interesting to prune and its even more fun to watch the results:  big, juicy fruit. I always look forward to making fresh red currant vinaigrette for my garden-fresh spinach and lettuce.  In addition to their usefulness as a food, I appreciate the various currants for the impact they make in my garden, with their interesting branch structure and beautiful berry display.

Red Currant (Ribes rubrum) 

 

Ripe red currant berries in Sylvan Lake, AB

If its fruit production that you’re after, red currants are high maintenance.  But its worth the work, and if you enjoy pruning, as I do, you won’t mind pruning these plants twice per season.

Established Plant Pruning

In summer, prune each new lateral shoot to 5 leaves near the end of July.  Leave the leaders alone at this point.  After harvesting, in late fall or winter, cut back all new leader growth to about 3” (or the closest bud).  Cut all summer-pruned laterals back to one bud. Remove any dead, diseased, or broken branches as well.  When you prune, think about the overall shape and framework of the shrub, pruning to buds that face in the direction you want the branch to travel.  Generally, I prune to outward facing buds.

Insects & Disease

I bought four red currants at a going-out-of-business-sale a few years ago and knew almost nothing about the plants at that time, since they generally fall out of the realm of ornamental plants.  I was warned that they were prone to aphids.  That warning was correct.  Red currants become infested with aphids, while everything else around them is fine.  The first year I sprayed the leaves with a neem-based product with poor results.  Next I went straight for the Malathion, which worked very well.  There was a small resurgence in the aphid population a couple of weeks later, but to a lesser degree.  Last spring, I tried a soil applied systemic insecticide in late May, and I had absolutely no aphids on any of my plants all season long.  This is the treatment I recommend, but beware the pre-harvest interval for using such chemicals, so as not to consume pesticide residues.  If you’re not a fan of insecticides, try insecticidal soap, and be prepared to spray weekly. Also, I have had reports of foliage damage after using insecticidal soap.

So far, my plants have been disease-free.

Renovation

After realizing that red currants do not make the most beautiful landscape shrubs, I moved some from my ornamental garden to somewhere near the compost, for educational and fruiting purposes only.  Two of the transplants suffered the following season and new growth eventually started to die back.  But the new shoots looked healthy.  So I pruned out the transplanted shoots, left the new ones, and the plants look fine. The point:  I believe that renovation to grade should be okay on older plants due to the vigorous nature of red currants.  Prove me right or prove me wrong, then let me know.

Irrigation & Fertilization  

My red currants are surrounded by about 4” of mulch and I top it up as it degrades. The soil stays moist beneath the mulch and I rarely need to water (once last season!)  Moist, well-drained soil is preferred.  I fertilized my currants with 20-20-20 the first season. Last season I used a combination of humic acid mixed with mycorrhizal fungi.  This season, I’m adding a product called KelpGro (an organic Kelp based fertilizer from BC) to the mix.

Golden Currant (Ribes aureum)

This is a low maintenance shrub, best planted in an area large enough to accommodate its mature form (5′ x 5′), and left alone.  This really is a multi-season ornamental plant, with a great flower display, interesting and edible berries, and often beautiful fall colour.  It is also native to Alberta, very hardy, and insect and disease resistant.  A great choice for a Prairie shrub bed.

Overgrown shrubs can be reinvigorated in a manner similar to lilacs, tatarian honeysuckle, or cranberries.

Alpine Currant (Ribes alpinum)

I have mixed feelings about alpine currant.  I first learned about this species in college and my plant instructor mentioned that it can be used in topiary (ie. pruned into interesting shapes).  It was years before I found a specimen healthy and vigorous enough to use for such a practice.

Pruning

Healthy plants respond well to shearing and “cloud pruning.” 

Renovation

Old, overgrown rows or specimens can be cut back hard to a few inches above grade.  New shrubs will regenerate.

Irrigation

Do not over water these plants or they will die.  Their native habitat is dry, windy, alpine slopes.  They cannot tolerate “wet feet.”  I know, I nearly killed a few plants one year by direction the downspout from the house in their direction.  They only started coming back two years later!

(c) 2011, Shane LePage, Wild Rose Tree Service, Red Deer, AB