What Causes a Cedar to Turn Orange?

Cedar trees -- Cedrus spp. -- are evergreen conifers from the pine family. The trees adapt well to a range of climatic zones and their mature forms are suited for larger, open spaces rather than small gardens. Though cedars grow well with minimal care and have few problems, they are prone to a fungal infection that gives the trees an orange look.

Cedar apple rush is a fungal disease of cedars and is caused by Gymnosporangium juniperi-virginianae. The fungus requires two major hosts, apple and eastern red cedar, in order to complete the life cycle. The spores produced by infected apple trees infect cedars and those produced by cedars infect apple trees.

The disease is characterized by the appearance of galls or hard, brown swellings of tree tissue on the tips of the branches. With the arrival of spring, the galls start to swell and produce rust or orange-colored gelatinous horns that are actually fungal spores. The spores travel to apple trees in the area, appearing in the form of yellow spots on the foliage and fruit that gradually turns orange. The rust-colored horns on galls in cedars give the tree a general orange look.

Cedar apple rust spores start to spread with moisture. Keep the trees well-pruned for adequate air circulation in all areas of the tree. Plant in a sunny and well-ventilated site. Prune and remove all visible galls on cedar trees during fall and early winter. Avoid using infected pruning tools on healthy trees. If you are planning on growing apples and cedars on your property, choose disease resistant varieties in order to minimize chances of infection in the future.

Use products containing the fungicides myclobutanil or triadimefon for effective control of cedar apple rust. Start application as soon as you notice the appearance of the orange tendrils on the galls. Repeat the application every seven to 10 days for as long as the galls are active and continue to produce the spore tendrils.