Sumac Has Yellow Spotted Leaves
I have a sumac plant that was very hardy the first couple of years. Now it has very sparse growth on the branches and about 30% of the leaves have started to turn yellow with spots and fall off.
Fungal leaf spot diseases can cause the leaves to drop prematurely. These are usually not life threatening and do not require treatment. The damage looks devastating since sumacs are mostly leaves with a few un-branched stems. So when the leaves start to drop the plant looks pretty sparse. I would not be concerned. Rake and destroy fallen leaves. If the plants show signs of dieback or discoloration on the stems your plants may also be suffering from a wilt or canker disease. Prune 9 to 12 inches below the dead and discolored areas or right back to ground level. Disinfect tools between cuts. If dieback continues you may want to call in a landscape professional to examine your sumac and diagnose the problem.