All of my service berries have a rusty spot all over the leaves starting around mid June. This has happened for the last few years. Can you help me ID what the issue is and suggest ways to remedy it?
Thank you for contacting the Toronto Master gardeners concerning you serviceberry.
As serviceberry is in the rose family (Rosaceae), it is susceptible to many of the same disease and insect pest problems seen in other species within the family (e.g. apples and pears). Entomosporium leaf spot (Entomosporium sp.) may cause serious spotting and partial defoliation on some selections, especially following rainy weather. Cedar-serviceberry rust affects twigs, buds, fruit and foliage and can disfigure these plant parts or result in witches’ brooms. Your photo is quite blurry, as a result it is difficult for me to see the spots that you describe.
Serviceberry grows best in full sun or mostly sunny sites and prefers moist, well-drained soil and requires watering regularly during the summer. While the serviceberry can adapt to living in alkaline or neutral soils, it much prefers to be planted in acidic soils. It is under greater stress when growing in clay soils.
Your serviceberry could be suffering from either leaf spot or rust.
See this useful article for description, advice and management strategies: https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-diseases/cedar-apple-rust
The Missouri Botanical Garden article: https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/rusts/cedar-apple-rust.aspx provides clear information on the rust cycle which requires two hosts: a juniper and serviceberry. The fungus responsible for infecting serviceberry is cedar-hawthorn rust (Gymnosporangium globosum) While the common names of the various rust infections are termed cedar- the alternative host, eastern red cedar’s botanical name is Juniperus virginiana. The life cycle is explained and Integrated Pest Management Strategies are listed.
The University of Massachusetts article https://ag.umass.edu/landscape/fact-sheets/cedar-apple-rust includes a description of the disease cycle and management strategies.
This website gives a description of both leaf spot and rust, it’s prevention and control.