Unless your shrubs and trees have a history of trouble with diseases, I can't think of any reason they should be sprayed at all. Even if the plants were susceptible to disease, a more sustainable approach than annually applying fungicides and other pesticides would be to select disease-resistant plants that will thrive in your garden's conditions without that sort of intervention.
Spraying, depending on what is being sprayed, can be a hazard to human health and the environment. You may be able to stop your spraying program entirely by instituting good garden practices, like cleaning up debris and providing good air circulation around the trees, and avoiding overhead irrigation.
Examples of nonchemical ways to manage fungal problems that may affect ornamental cherry are provided below, from Washington State University Extension's HortSense website:
"Brown rot is a fungal disease which initially infects the flowers. The petals turn light brown, develop water-soaked spots and may have tan or grayish areas of fungal spores. Infected flowers often remain attached to the plant, spreading the disease to small twigs and branches. Infected twigs and branches are often observed in the summer as flagged, dead leaves and twigs. Infected branches develop cankers which may produce gumming (leaking sap) or may girdle and kill the branch. Most brown rot cankers develop with a dead twig at the center where the initial branch infection occurred. Fruit can also be infected, dry out, and hang in the tree. Tan or gray fungal spores may be found on infected blossoms, fruit, or twig cankers. Ornamental and fruiting stone fruit trees are affected.
Select Non-chemical Management Options as Your First Choice!!
- Avoid wounding trees.
- Clean up and destroy fallen flowers and other debris beneath trees.
- Remove and destroy all infected twigs and branches during the summer, making pruning cuts well below infected tissues."
Similarly, here are their recommendations for managing Coryneum blight or shothole:
- Avoid overhead watering, as leaves must be moist for infection to occur.
- Prune and destroy dead buds and cankered twigs if present.
- Rake and destroy infected leaves.
Again, for cherry leaf spot:
- Avoid overhead watering. If overhead irrigation is necessary, limit it to times when foliage can dry quickly.
- Rake and destroy all fallen leaves and debris under trees.
- Space plantings and prune to provide good air circulation.