A disease called fire blight, caused by a bacterium (Erwinia amylovora), has these symptoms. The causal bacteria are spread by wind-blown rain and insects. Fire blight is difficult to control in highly susceptible varieties. Avoid excessive nitrogen fertilizer. The blighted shoots and blossoms can be pruned out as they appear if you sanitize the pruning shears by dipping them in a 10 percent bleach solution or 70% isopropyl alcohol (rubbing alcohol) between cuts. Otherwise, prune the blighted shoots …
What causes the yellow leaf spots that later develop a brown center on my apple leaves?
This a fungal disease called cedar-apple rust. Cedar-apple rust is a common disease of apple and crabapple. The fungus that causes the disease, Gymnosporangium juniperi-virginianae, is unusual because it must spend a phase of its life cycle as a parasite on Juniperus species, such as red cedar or ornamental junipers. Control: Grow resistant apple or crabapple varieties. Apple varieties that normally show good to excellent resistance to cedar-apple rust include ‘Red Delicious’, ‘McIntosh’, ‘Arkansas Black’, ‘Winesap’, ‘Mollies Delicious’, ‘Spartan’, …