Answer: It's difficult to diagnose a problem without seeing it, but I'll offer two possibilities for the rusty looking fig leaves. First, it may be a symptom of water stress or over-fertilization. If the leaves have rusty red splotches mostly along the margins or at the tips, this is probably the cause. Secondly, there is a fungal disease that attacks fig trees and can cause rusty looking splotches on the leaves. This disease doesn't affect fruit production but can defoliate trees.
Fig rust is caused by Physopella fici. Fig rust first appears as small, yellowish-orange spots on the leaves. These enlarge slightly and may become very numerous as the season progresses. Rust is controlled with neutral copper sprays. One or two applications made in May or early June usually keep trees in fairly good condition until after fruit ripens. In very wet seasons one or two additional applications may be necessary. A good index for spraying is when the first leaves on the tree have reached full size. The second spray should follow in 3 to 4 weeks. It is extremely important to get good leaf coverage with the spray material.
While it is too late this year to protect your trees from rust, you can rake up and destroy the fallen leaves to prevent the spread of the disease and then spray your tree with a fungicide next spring.
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