By Stephanie Butcher, Coweta County Extension Service
Question: I saw a tree that has a strange looking orange blob on it. What is it?
Agent: It sounds like you saw a cedar tree infected with cedar-apple rust, a fungal disease. Those bright orange blobs start out as brown galls (sometimes called cedar-apples) and aren’t usually noticeable unless you are specifically looking for them. They don’t become obvious until warm, spring rains moisten the gall and they explode with what looks like orange worms coming out of the gall. This is when billions of spores are released and can infect apple trees.
This is a very interesting disease because it must have two different types of hosts in order to complete its life cycle. Half of its life cycle happens on a juniper specie like red cedar or ornamental junipers and half of its life cycle happens on rosaceous plants like apple, crabapple and hawthorne.
Cedar-apple rust can be a problem for anyone growing apples. In late spring, apple trees that are infected with the disease will have yellow or orange lesions on the upper side of the leaves. Infections can cause small, deformed apples and can cause early fruit drop. More serious infections can kill the tree.
Fungicides can be applied to apple trees prior to infection to control the disease, but the best method of control is to prevent it by planting resistant varieties. These include Arkansas Black, Mollies Delicious, and Granny Smith. A few highly susceptible, on the other hand, include Jonathan, Golden Delicious, and Rome.
Although apple trees can be infected more than a mile away from the host plant, most infections occur from cedars that are located within a few hundred feet of the apple tree. If wild or abandoned cedars or crabapples are present, then you can remove the entire plant. If you only have one or two small cedars that are small and easily accessible, then you can remove existing galls by pruning.
For more information on cedar-apple rust or resistant apple tree varieties, call 770-254-2620 and ask for the publications, “ Home Garden Apples ” and “Cedar-Apple Rust”.
The University of Georgia College of Agricultural & Environmental Sciences is an equal opportunity, Affirmative Action, Veteran, Disability Institution.”