By Mike Allen
Written for the Winnipeg Free Press September 19, 2007
Each fall I get numerous questions about tree and shrub problems that occurred during the previous summer months. here are a few common problems in 2007.
Many people have called me up asking, ‘Why are there so many dying ash trees’? The calls come from within as well as from outside Winnipeg. The good news is that the ash problems are not arising from the deadly emerald ash borer – a beetle that is killing millions of ash trees in southern Ontario and throughout the United States in the Great Lakes area. The ashes are suffering from heavy infestations of scale insects which may be accompanied with heavy infections of anthracnose disease.
This year in southern Manitoba, I have observed ever growing numbers of Leucanium scale insects feeding heavily on the twigs of ash trees causing them to die. In addition, ash trees have always had fluctuating infection levels of leaf anthracnose disease either with or without high levels of scale infestation. This disease is usually not a problem as it causes either brown blotches in the leaves or causes the leaf stalk and leaves to prematurely separate from the twig. This year, I’ve noticed anthracnose killing the leaves of Manchurian ashes. I now see a twig anthracnose disease component especially in Mancana ash trees that have had repeated anthracnose leaf infections. The disease appears as a linear swelling in the twig with the twig bark splitting into fine parallel cracks called ‘lesions’ often with patches of maroon colour. As the disease intensifies in the twig, these lesions open up and become spore producing cankers. The spores will travel through the air and infect other ashes including the originating ash tree.
The best means of controlling the scales is to spray the entire tree with dormant oil. The best means for controlling leaf anthracnose is to spray dormant lime sulfur fungicide. Both sprayings should be carried out in mid-April before the buds open in the spring. The buds, twigs and branches should be thoroughly soaked with dormant products. The lime sulfur can be mixed with dormant oil (if scale and mite control are needed) and sprayed on the tree together. Spraying a fungicide such as copper sulfate or Daconil in early June may help control the early stages of the twig disease.
SPRUCE, PINE AND CEDAR TREES / SHRUBS
In preparation for winter property owners with coniferous evergreen trees and shrubs such as spruce, pine and cedar should be prepared for heavy evergreen needle and evergreen leaf drop following two very dry summer seasons. The major culprit for this is Cytospora fungal canker or what I refer to as white blister disease. It occurs primarily in spruces but the disease can also be found in cedars and pines. In spruces and cedars the needle/leaf browning is also worsened by spider mite feeding. There are many problems affecting coniferous evergreens beyond these two, and proper treatments and timing of treatments require proper diagnoses. Knowledgeable aeration and fertilization slows down the long term killing Cytospora disease; and monthly pressure washing will remove spider mites and other pests in the trees and shrubs. Remember to thoroughly water the roots of coniferous evergreens before the ground freezes.
Mike Allen is a consulting urban forester, a certified I.S.A. arborist, and owns Viburnum Tree Experts. He makes house and garden visits to assess tree and shrub problems. He can be contacted by calling 831-6503 or by e-mail at firstname.lastname@example.org. You can also mail questions to Mike Allen, c/o Newsroom, Winnipeg Free Press, 1355 Mountain Ave., Winnipeg, MB, R2X 3B6. His web site is www.treeexperts.ca