My small cherry tree produced about 12 cherries and then I noticed little reddish “ants” on the leaves. Soon the leaves turned yellow and fell off. I want to save this tree because it was planted by my neighbours after my daughter died three years ago.
Your description of little reddish insects crawling on your cherry tree and yellowing leaves is somewhat suggestive that a sucking insect like mites or scale, both of which can affect cherry trees, has befallen you beloved cherry tree. Besides yellowing of the leaves these insect pests can also cause curling and twisting of leaves, and wilting of tender shoots and leaves.
Mites look like tiny red or brown spiders and feed on the underside of leaves. The crawlers, the mobile larval stage of scale insects, are often described as yellow, however, they are difficult to see with the naked eye. Look out for the immobile female scales which look like little round humps that may give the branch surface a rough look.
In the home garden, damage by these insects can be prevented with the application of dormant oil in spring before the buds break. Insecticidal soap can be applied to control a mite infestation. Please use both products according to the instruction on the package.
In addition to these products (both are approved under the Ontario Cosmetic Pesticide Ban and can be purchased in a reputable nursery) good cultural practices as described in this previous post published on this website and in this article Fruit Trees for the Home Garden by OMAFRA (the Ontario Ministry of Agriculture, Food and Rural Affairs) will help ensure a long and healthy life of your cherry tree.