Would these white stuff on leave (they happened last years, too) hurt tree? Pics. 1 & 2 Is this dogwood tree? According to my record this is barlett pear. (But they don't look like pear at all. In 2012 I bought 100 Kentucky coffee tree seedlings but end out they're birch trees.) These white stuff also appears on one oak tree, Pic. 3. (I've dug out many small oak trees from our woods and moved them to fill missing spot on my tree-grow plan.)
Hello. This is powdery mildew, a fungal disease. Unfortunately I cannot ID the tree because of the disfigured leaves. When this pathogen is present it is important to pick up and remove all the debris that falls from the tree. When rain hits the leaves on the ground it releases spores that re-infect the tree. It may not kill the tree but chances are the tree will continue to be infected and will be unattractive. There are treatments but it is time consuming and difficult for a home owner.