Apple tree fungus?
Hello, we have an apple tree with some small (new growth) limbs that have dead leaves. I have included a picture of a leaf that is not dead yet, but has some brown spots on it. I cannot find any insects on the dead leaves. Is this problem due to the hot and humid weather we have been having? The larger limbs seem okay. We pruned this tree early this past spring to improve air flow.
Iowa County Iowa
The spots on the apple leaf are likely due to cedar-apple rust. Cedar-apple rust is a fungal disease. The fungus requires both an apple or crabapple and a cedar (juniper) to complete its life cycle. Apple and crabapple cultivars differ in their susceptibility to cedar-apple rust. Some cultivars are susceptible, others are resistant.
On cedar, the fungus produces reddish brown galls that are up to golf-ball size on young twigs. During wet spring weather these galls swell and begin to push out bright orange gelatinous tubular structures. Wind carries fungal spores from these gelatinous structures to susceptible apple and crabapple cultivars. On apples and crabapples, cedar-apple rust produces yellow spots on the foliage. Cedar-apple rust on apples and crabapples is most severe when there are frequent rains in spring.
On a positive note, cedar-apple rust does not cause serious harm to apples and crabapples.