I planted a serviceberry (Amelanchier canadensis) tree in 2007. I live in mid-town Toronto. The tree gets about an hour of sun in the morning and another 3-4 hours in the afternoon. I don’t water very often because most of my garden is drought tolerant. The garden is sloped, so there is no standing water, but we have had record rainfall this year. The soil is loamy, no sand or clay. I dig a bit of compost into the garden, usually once a year, and there is some mulch to keep weeds down. There are perennial geraniums, hosta, Cotoneaster dammeri and dense yew growing in the same garden. The serviceberry has been doing fine until this year. Now it has spotted leaves and something scaly on the the branches, and a few dead branches. Do you know what the problem is, and whether I should treat it or remove the tree? Three photos, one of the top of the leaves, one the underside of the leaves, and the other is the branches.
Thank you for reaching out to Ask a Master Gardener by Toronto Master Gardeners.
There has been an unusual amount of rain this season which has had consequences, including, apparently for your Serviceberry. The “something scaly” visible in the picture is lichen, which will not harm the shrub but is a result of the increased moisture. “Lichens do not damage plants or rob the bark of moisture. They do not parasitize living plant cells, and studies show that there is no association with pathogens entering plant tissue and causing disease.”
There is at least one and possibly more things happening to your plant based on the appearance of the leaves. The obvious problem is powdery mildew which is causing the whitish cast on the leaves and possibly the early yellowing. The brown patches on the leaves may be sign of another problem but it’s not clear from the photographs exactly what that is. One possibility is rust; this article and the references below have more information on what to look for to confirm this diagnosis.
In most cases the impact of these diseases is cosmetic and the plant will survive. The easiest response is to remove as much infected foliage as possible as soon as possible and to ensure that in the fall all leaves are cleaned up and disposed of as garbage, not in compost or leaf waste. It is quite possible that next year under different weather conditions the plant will not show as many symptoms. Ensuring the health of the plant through other good gardening practises (proper watering and nutrition) will also help.
If you have premature defoliation caused by leaf infections it is possible that bare branches are not actually dead. You can scratch a small area of the bark of a branch that seems dead with a key or secateur blade to see if there is any living green tissue; if in doubt, scratch a branch that is obviously alive to compare. If the branch is alive it may sprout leaves later in the season or next year. Given that your site is well-drained it seems unlikely that excess water would have led to the death of the branches. There is always some natural attrition of branches on plants as old as yours.
If you are so concerned about the appearance of the plant as to consider removing it, you can contact a certified arborist who is knowledgeable in disease diagnosis and integrated pest management for an opinion before doing so. Certified arborists who are integrated pest management specialists can apply treatments to your plant that may help but hopefully this intervention will not be necessary.
Citations:
Landscape: Cedar-Hawthorn Rust | Center for Agriculture, Food, and the Environment at UMass Amherst
For a comprehensive review of diseases see: Shadbush Serviceberry Amelanchier (ct.gov)
The above article contains links to US websites that include information about pesticides
(chemical controls). This information does not apply in Canada. The use of pesticides for
cosmetic purposes in home lawns and gardens is strictly controlled by Ontario law. The link
below has information about pesticide use in Ontario, and includes the Allowable List of
active ingredients that can be used. The Toronto Master Gardeners fully supports and
endorses the Ontario pesticide ban. We recommend only commercial products whose
ingredients are on the Ontario Allowable List and only when these products are used
according to the directions on the label. We do not endorse home remedies.