Q: I have a problem every year on certain dogwood trees. The effect is of a tree with beige blooms …..which should be white. There are many small red dots on sometimes highly disfigured bloom petals. Should I worry?
A: The dogwood problem is spot anthracnose. We’ve had a wet spring… so leaf spot diseases are going to be a big problem this year.
You can use chlorothalonil (click for sources) or mancozeb (click for sources) to protect against leaf infections….but it’s too late once you see the spots. Apply 3 or 4 sprays during leaf expansion in the spring, at 10-14 day intervals. The causal fungus overwinters on infected twigs and fruit. Be sure to avoid high nitrogen fertilizers which stimulate succulent new growth.
Some dogwood cultivars are resistant to this disease and to powdery mildew. Check this site for a list: