Blast lesions often start at the leaf petiole. Leaves affected by blast wilt rapidly and dry on the tree. The dried leaves may fall leaving the leaf petiole behind or the entire leaf may remain stuck on the tree. In severe attacks, twigs are girdled and killed. If the twig isn t killed, callus will form at the edge of the twig lesion and the diseased spot will be covered by a reddish brown scab or crust.
Blast is most severe on the exposed sides of the tree.
In our area, usually the south side and the tree tops are most seriously affected. Complete coverage using 10-25 gallons of spray per mature tree is the recommended rate. Commercially available fixed copper materials are not as persistent as a Bordeaux spray. However, they are much easier to use and are readily available. Sprays applied now will still help protect leaves and shoots from late winter and spring storms.