We have a tree in our mostly sunny backyard in the Danforth area. Over the last couple of years it has started to look more and more sick. We enclose a picture of what some of the leaves are looking right now. A garden center suggested this was mealy bugs but we can see no bugs and that doesn’t seem likely to me. Should we get rid of the tree or can it somehow be treated ? The grass close to the tree also seem like it is sprayed with white chalk. Is that related.
Thank you for contacting the Toronto Master Gardeners about your tree pest / disease. To make a definitive diagnosis we would need to now what type of tree you have.
Infestation with mealy bugs, as suggested by your local garden center, is a possibility. Mealy bugs are sap-sucking insects that can be found on all plant parts but are often on the underside of leaves. Mealy bug damage can cause yellowing leaves. They excrete a sweet sappy liquid called honeydew which attracts ants and often turns dark with mold growth. If you see no signs of honeydew or bugs on the underside of the leaves then infestation with mealy bugs is less likely. More information about mealy bugs can be found here.
There are fungal diseases such as powdery mildew that cause yellowing leaves, but also typically cause leaf spots (your photo shows dark spots on the leaves). Powdery mildew’s main characteristic is the powdery-like spores on the leaf surface. Whether or not this could be related to the chalk-like substance on the ground at the base of the tree is unclear.
Nutrient deficiencies are another possibility. More systemic issues such as chlorosis caused by iron deficiency would affect the entire tree. Your picture shows that many other leaves are ok, making this unlikely. A soil test would give you information on what is available to the tree. You can find soil testing facilities with this link: http://www.omafra.gov.on.ca/english/crops/resource/soillabs.htm. The University of Guelph also does testing.
If this is a tree you feel strongly about keeping then it may be helpful to engage an arborist to have a closer look. Landscape Ontario can provide a list of arborists in your area Landscape Ontario. Alternatively, if you are thinking of replacing the tree, look for a native species suitable to your sunny location. Some suggestions can be found at https://landscapeontario.com/landscaping-with-native-plants.
In the meantime there are a few things you can do to optimize your tree’s health. Add an inch or two of compost around the tree base – being sure not to pile it up against the trunk. Compost will add some nutrients to the soil. Ensure the tree is adequately watered and mulch around the base to help retain moisture – again ensuring mulch is not touching the trunk. More information about summer tree care can be found at LEAF Leaf – tree care including the ideal way to mulch trees LEAF – mulch.