Rust infections are a common problem on deciduous trees. The symptoms of a rust infection can be seen as small reddish or yellow bubbles or postulants on the lower surface of leaf. The rust usually appears late in the season and may cause leaf yellowing, early leaf drop and in cases of severe infections, significant defoliation throughout the tree.
Since Rust generally appears late in the season, a good sanitation program, which includes raking and disposing of all leaves after they drop in the fall, is usually adequate to prevent re-infection the following year. If additional control is required, or as a proactive preventative treatment, during spring bud break spray the tree with Liquid Copper Fungicide. Repeat the spray twice more every 14 to 20 days. In more serious cases of rust disease or if the disease re-appears over serval years apply Monterey Fungi Fighter early in the spring shortly after bud break and again mid-season or at first signs of symptoms.