Answer: Leaf drop and casting of fruit are common responses of a fig tree to leaf diseases and root problems. Fig leaves often succumb to fungal diseases in the south. The most common of these diseases is rust. While you can spray leaves with a liquid sulfur product to discourage these diseases, it is not generally recommended. Sulfur, a weak fungicide, can burn plant foliage in the heat of summer, and these diseases seldom result in serious damage to the fig bush.
Other things with can causes a fig to drop its older leaves are drought, soggy soil conditions (roots need oxygen to survive), and nematodes. Sandy soils are the most likely place to encounter nematode infestations. They attack the fig roots, causing them to be severely damaged and very inefficient in taking up water and nutrients.
You can't do much about nematodes in the soil around a fig tree. However, some people have had decent results by mulching with several inches of compost each year to provide the tree a rich, medium in which to develop new roots, and to encourage natural enemies of nematodes in the soil. It is especially important with a nematode infested bush to keep the soil well watered to avoid further stresses.
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