Hello Eileen

If you are growing your cherry trees in order to harvest the fruit then yes, you will want to establish a spray schedule for your trees. If you are growing your cherry trees only as ornamental, or you do not harvest or use the fruit, then you have no need to spray for pests. Fruit flies will not kill the trees.

When and how to spray the trees is timed by the stage of development of the flower buds. Here are some publications with clear pictures to show you what bud stages look like, and these publications have a spray schedule to guide you.

You will want to prune, and establish a spray schedule for your trees that you want to harvest for fruit.

Here are some pest and spray references to get you started- please see the section on cherry trees:

Managing pests - with pictures of bud stages for spray schedule

https://www.extension.purdue.edu/extmedia/ID/ID-146-W.pdf

Organic pest management

https://s3.wp.wsu.edu/uploads/sites/2070/2019/09/EM066E.pdf

Here is more about fruit trees and how to care for them. P,ease see the cherry tree section for your trees.

Midwest Home Fruit Production guide

https://plantpathology.ca.uky.edu/files/mw_home_fruit_productn_b591.pdf

Pruning old fruit trees—. https://extension.oregonstate.edu/gardening/berries-fruit/restore-those-old-fruit-trees