Rust Fungus on Tree Bark

Pines

• Sweetfern Rust is a fungal disease that often attacks pine trees. it is caused by spores that spread from sweetfern and sweet gale trees. These spores are blown by wind and infect pine needles, then move into the branches and trunk of the tree. This results in swelling and the emergence of cream colored structures that rupture through the bark. Stalactiform Rust infects jack pine trees and causes elongated cankers (sunken, discolored bark). Other fungal rust diseases in pine include White Pine Blister Rust and Comandra Rust. Remove cankered branches to counter these problem.

Cedar, Juniper and Apple Trees

• Many apple trees are affected by a number of rust fungi that causes bright orange lesions on leaves and branches. Depending on the fungus causing the symptoms, the disease may be called cedar-apple rust, quince rust or hawthorn rust. The lesions may produce spores on the underside of leaves. Stems and bark may be affected as well, resulting in swelling and rust spots. This fungus completes its life cycle on the cedar tree. The disease also appears on juniper trees, reddish-brown swelling spots appear on branches and twigs, which release spores in wet weather.

Ash Trees

• Ash rust is a disease that infects green, white and black ash trees and is caused by the Puccinia sparganioides fungus. Spores originate from grasses and spread to ash trees, resulting in swelling of leaves and twigs. Leaves take on a distorted or necrotic appearance and may drop from the tree. Orange spots containing spores appear on leaf surfaces. Usually this disease is not a serious detriment to ash trees.

Control

• Many rust diseases are controlled with copper-based fungicides applied in summer. Apply more often after rainy periods. Cover leaf entirely with the fungicide. For the purpose of controlling Apple Rust disease, use sulfur fungicide on apples, and chlorothalonil on ornamental crab apples. Prune infected plant parts to eliminate spores and provide ideal conditions for the tree in general.