The last two years of summer have been hard on the health of green ash trees in particular. All over southern Manitoba, younger ash trees of this species have been particularly weakened by leaf anthracnose fungus disease and by the lack of soil moisture in the root zones. Older trees have also been susceptible to the disease.
Many ash trees were weakened four to six years ago by heavy infestations of brown dome-shaped insects called lecanium scales. The scales are no longer a problem this year. Today the leaves of stressed trees have curled, tattered leaves with brown areas killed by the fungus disease.
Ash-tree stresses have caused numerous large dead branches in the crowns of thousands of trees. Leaf anthracnose can be controlled with spraying an approved fungicide twice about two weeks apart in June.
Lately I have seen the anthracnose disease showing up as a twig fungus that can cause the twigs to grow abnormally and die. There is no control for this component of the disease. All that can be done is to prune off the dead twigs. Unfortunately the longer these problems are ignored, the more these trees get stressed. Many of the smaller green ashes I see now will simply not live to become larger shade trees.
If you or someone you now has a younger struggling green ash, get the tree thoroughly watered as soon as possible. Actually, this applies to all young trees of all species. Later in early October, have the tree properly fertilized. See my columns of last year on how to best fertilize a tree or get in touch with me for more information. Use a tree fertilizer such as 10-52-10 that will stimulate new roots, thereby giving the tree an opportunity to recover. Never use fertilizer stakes and never use root feeders for trees. They are simply not effective.
Water the tree thoroughly again in mid-October before the ground freezes. Repeat all treatments in 2012.
Michael Allen M.Sc.F., RPF is a consulting urban forester and certified arborist. He owns Viburnum Tree Experts, a Manitoba company that provides objective assessments of the condition and the care required for trees and shrubs on home and business landscapes. He can be reached at 204-831-6503 or viburnumtrees@shaw.ca His website is www.treeexperts.mb.ca
