July 10, 2004 Articles No Comments

By Mike Allen

Written for The Prairie Arborist, Prairie Chapter of the International Society of Arboriculture (ISA), Issue 2, Spring 2004, pp 8 – 9

I have noticed as have many people in southern Manitoba, that there have been more problems with trees and shrubs in the last five years than there have in the previous five years. Climate is certainly a factor in this, but age of tree and type of tree affected are others. Urban areas have suffered worst than rural areas except residential acreages within 10 to 15 km of urban municipal boundaries. The landscape damage caused by these problems is significant. Most property owners are not even aware that their trees have major problems. The information presented here relates to southern Manitoba, but I am certain the majority of these problems also show up in the other Prairie provinces.

During this period the following diseases have made substantial impacts of woody plants: Cytospora fungus canker disease in boughs and trunks of Colorado blue, white spruce and balsam fir; Sirococcus tip blight disease in the boughs of spruces, Scotch pine and mugo pine; black knot disease on all parts of Schubert choke cherry; hawthorn gall rust on the twigs and foliage of Rocky Mountain juniper varieties; Dothichiza fungus canker disease on the trunks of columnar Swedish aspen and Tower poplar; Botryosphaeria fungus canker disease on the trunks of apple and crab apple; Botryosphaeria twig blight cankers on the stems and branches of dogwoods; Leucostoma (Cytospora) fungal canker causing gummosis on the branches and trunks of plum, apricot and cherry; and, numerous Anthracnose leaf diseases on various deciduous trees. There are many more diseases but this group seems to have outpaced many others in urban areas.

Various pests have left their mark on woody plants within the last five years as well: spruce spider mites on the needles of Colorado blue spruce and white spruce; Fletcher scale insects on the foliage of ornamental cedars (Arborvitae); sawfly larvae on the needles of spruce; Lecanium scale insects primarily on the twigs of American elm and green ash; elm span worm on the leaves of bur oak especially and elm; moths of the pitch mass borer in the trunks of Colorado blue spruce, white spruce and Scotch pine; and, two-lined chestnut borer in the trunks of bur oak.

A few pests and diseases have been with us for some time and seem to worsen in some areas more than others such as Dutch elm disease on American elm; spring and fall cankerworms on deciduous trees such as Manitoba maple, American elm, bur oak and green ash; and, bronze bark borer on weeping white birch. I would now add Cytospora fungal canker in spruce and Botryosphaeria twig blight canker of dogwood to this list as I believe these diseases have reached epidemic levels in urban areas.

Finally there is one disease which does not have an organism associated with it. The physiological disease is called chlorosis. Typically plants affected have yellow leaves with more of less prominent green veins. The cause is usually an iron nutrient deficiency in the soil.

Many property owners suspect or definitely know they have a tree problem, but are unsure what is necessary to remedy the problem. They rely on the company that is doing the work to give them an honest assessment of the work that needs to be done. Talking to three or more tree service firms will help pin point the nature of the problem and the best solution. I always recommend ISA arborists. Sometimes I run across three different definitions with three different solutions by non-ISA trained arborists. ISA trained and certified arborists should be the professionals that the public can go to and feel confident that the arborists’ recommendations are the very best in the tree industry.

In my experience, a large number of arborists can not identify all these pest and disease problems. Both the problems and possible solutions go unrecognized. One should certainly ask oneself about the efficacy of treatments given when the true problem is not properly diagnosed. Most of these problems have treatments. Keeping trees and shrubs healthy should be the backbone of every home landscaping care program. Arborists should include an annual course in their business that increases and improves their knowledge about tree interactions with their environment. Most ISA courses do that. I am recommending that the ISA Prairie Chapter focus more of its courses on the practical identification of pests and diseases, and follow through with traditional and regulated treatment procedures. Round table discussions at the end of the course would ensure input from all those who wish to contribute their ideas as well as receive feed back from others.

Written by treeexperts-mb