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Renovation & Design

Continuing issues with Japanese tree lilacs

Lilac leaves with Anthracnose and Microsphaeropsis disease.
Nutrient stressed yellow tree lilac leaves.
Anthracnose fungus disease on Japanese tree lilac leaves.

In my Aug. 23 article, I wrote a piece on Japanese tree lilacs in response to many inquiries from readers who were enduring problems this summer from this otherwise beautiful tree species.

In that column, we discussed the role of adverse weather conditions on the Japanese tree lilacs. I have had suspicious samples analyzed by the Manitoba Crop Diagnostic Centre. There is a common, normally non-pathogenic disease with the scientific name of microsphaeropsis present in many of these trees.

There is not much information on this disease, but I believe in part it is responsible for a great deal of leaf, bud and twig damage on tree lilacs. It seems to take advantage of previously stressed trees that have been affected by extremes of dry and wet weather in addition to early spring deep-cold weather. Both the buds and twigs were killed by these extreme weather conditions.

Late in the summer, anthracnose disease started to infect the leaves and leaf stems. Trees that have not been able to get their required allotment of nutrients from the soil also show stress and are likely targeted by insects. I am presently investigating the presence of wood borers damaging and deforming the trunks of lilacs.

In my last piece on the lilac problems, I recommended the trees need fertilizing this fall. I have included information below on how to fertilize trees. Follow these directions for fertilizing trees in the spring or fall.

For most trees, it is important you or a licensed applicator inject a suitable tree fertilizer (ideally high -- up to 30 per cent -- in slow-release nitrogen such as 20-20-20 or 21-7-7) into the soil around the tree. For small trees, you will want to drill a pattern of one-inch diameter holes six to eight inches deep and 12 inches apart. For larger trees, you will drill holes 18 inches apart.

In both cases, use an area of the yard extending at least a distance of half the height of the tree from the trunk in any direction, not withstanding physical restrictions. The tree will be more or less at the centre of the pattern of holes. Stay back at least three to four feet from the trunk of large trees.

Add two tablespoons of dry tree fertilizer to each hole, which can be covered if you want. (As this will be impossible to do in sandy soils, contact me for further directions.) Close spacing of the holes might be necessary owing to the limited root feeding area near some trees.

If the leaves are yellowing with green veins, add one or two teaspoons of iron chelate powder to each hole. For coniferous evergreen trees, start drilling the holes more or less at the drip line and continue outward as described above. Drill holes when the ground is dry.

Do not accept a single row of soil injections close to the drip line, as some products erroneously indicate on their packaging. Do not use tree root feeders or fertilizer stakes, as the package directions will cause you to significantly under-fertilize the tree. Badly stressed trees and newly planted trees should be fertilized with 10-52-10 or an equivalent such as bone meal. The high middle number helps to restore damaged roots.


Michael Allen M.Sc.F., RPF (ret.) is a consulting urban forester, tree diagnostician 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 is available to visit homes and gardens. He can be reached at 204-831-6503 or 204-223-7709 viburnumtrees@shaw.ca His web site is www.treeexperts.mb.ca

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