Calgary has had a widespread epidemic of black knot for well over fifteen years and the problem is only getting worse. Apiosporina morbosa is the Latin name for this fungal pathogen which predominately spreads during cool moist weather conditions in the spring. Control of the disease in infected trees is best done by pruning out symptomatic branches that appear as if they have a burned marshmallow on them. Black knot does infect trees systemically which means that even if infected branches are pruned the disease will continue to proliferate within the tree until it is dead and removed.
Because of the natural riparian areas within the city of Calgary it is nearly impossible to completely control the disease as it spreads on native plant species most commonly the western chokecherry Prunus virginiana. The best way to cure tree diseases including black knot in Schubert chokecherry and mayday species is to plant disease resistant trees, in other words the answer is simple do not plant mayday or chokecheery trees because they are guaranteed to get black knot. If you have a tree with a severe infection consider removing and replacing the tree rather than delaying the inevitable. Trees that only have a handful of knots appear per year can be pruned and preserved until the infection worsens.
Keeping a tree healthy will also ensure better chances of success, water regularly when dry, improve soil and site conditions if possible, prune symptomatic and dead branches, avoid over fertilisation and high nitrogen fertilizers.
Trees around the world are faced with the assault of mother natures weather events on a daily basis, in most cases if this occurs in a secluded forest the damage is unnoticed and has little impact on human activity. When storms and strong weather events hit cities however trees are definitely likely to be damaged and have an adverse effect on our daily lives such as the September 2014 snow storm in Calgary. The September snow event wasn’t the first time snow and leafed out trees collided in a bad way in the Calgary, in the early 2000’s there was a snowfall event in May that also caused significant damage to trees throughout the city and I wouldn’t be surprised if such an event occurs again.
Wind is another force of nature which has caused significant tree and property damage throughout Calgary in the past, damage caused ranging from minor twig breaks to complete tree failure. There is a lot that we can do as tree owners to prevent significant damage to trees and reduce the consequences of tree failure leading to property damage.
Firstly properly planting appropriate species in ideal locations is one of the best ways to avoid most conflicts caused by trees whether caused by storms or not. Planting a tree near an overhead wire for example is an extremely poor choice for a planting location or planting any species of tree within 10feet of a building should also be avoided. Have trees regularly inspected and pruned for structure especially young trees, Dr. Ed Gilman from the University of Florida has done extensive scientific research proving that structurally trained trees suffer significantly less damage than unbalanced or improperly pruned trees in severe weather. When a snow event repeats itself the best thing you can do is get the snow off of your trees and shrubs as quickly and safely as possible. You could brush or shake the snow off of smaller trees and shrubs but on larger trees you are putting yourself at risk if you attempt to go near the tree.
I learned from Wade Hartwell, the founder of Golden Acre Garden Centres, that using water is the best way to rid trees of snow and frost on trees and shrubs. Using a garden hose and pressure nozzle spray the branches from the tips inward to alleviate the weight at the end of the branches first, as the water melts off of the snow covered tree you will see the limbs bounce back up before your very eyes.
Trees often get forgotten in the winter but there are many advantages to having them pruned in the winter. When the leaves have fallen the structure and direction of the growth of a tree is much easier to see and work on.
Certain diseases such as black knot, are best controlled in winter because the symptomatic branches are much easier to spot and remove. Diseases are also less likely to spread to other trees or through fresh pruning cuts during the dormant period.
Insects are also dormant in the winter which is why Elm trees can only be pruned between October 1st and March 31st in Calgary and all of Alberta. This is to prevent the spread of Dutch Elm Disease which is carried by elm bark beetles that are attracted to fresh cuts and deadwood of Elm trees. If you have a fragile landscape you can take advantage of the frozen ground to protect any potential impact on soft or delicate areas below the tree being pruned or removed.
Summer has so much to offer and so little time to give, so why not take advantage of the fact that you can work on trees and shrubs in the winter and save some of that precious summer time.
You may want to consider giving the shrub a fresh start often referred to as either rejuvenation or coppicing. The practice of coppicing involves the cutting of stems within a few inches from the ground to encourage regrowth from the basal stems and roots.
One of the major advantages of rejuvenation is that a healthy shrub with a healthy root system will grow back robustly and surprisingly fast, at this point you can retrain the shrub for desired appearance and shape. Most deciduous shrub species in the Calgary area respond well to being coppiced. For serious pest infestations such as oystershell scale on cotoneaster shrubs and hedges rejuvenation pruning is the only viable option for recovery. The most ideal time to coppice or rejuvenate a shrub is during the dormant period, this is also a great time to get rid of years worth of accumulated debris in really dense shrubs.
People often ask how we are able to prune dead branches in the winter when there are no leaves on the tree and the whole tree looks dead. With a trained and experienced eye there are four clear indicators to look for when determining if a branch is alive or not.
1 Look for buds, if a branch or twig has buds this is a clear indicator that the branch may be alive.
2 Colour can also be used to make the difference between a dead and live branch, the dead growth will be either lighter or darker in colour depending on the species and how long the branch has been dead for.
3 Check for bark texture, a live branch should have a plump and full appearance and the bark will be firmly attached to the wood. Branches that are dead or dying will have more of a shrivelled look from the absence of water in the bark and branches that have been dead a long time can also be absent of bark.
4 Flexibility is the final method we used is the first 3 still have not helped in providing a definite answer of whether the branch is dead or not, using a light flex as a test, a live branch will be pliable and remain intact and a dead branch will either break or not bend as easily because dry and dead wood does not have the same bending properties as live healthy wood.
Finally a bonus test is the temperature of a branch, we don’t really rely on this one because we prefer to keep our gloves on our hands in the winter. Dead and dry branches will be warmer to the touch than healthy live branches which have a degree of moisture content making them feel cooler.