Question
I bought a home which has four large mature{20+yrs.)in the yard.This spring I noticed a dark orange dust like material covering the branches, which, after a hard rain turned gelatinous in spots. What is this and is it harmful? I live in the pineywoods of east Texas.

Answer
This is a disease called cedar apple rust.

During warm rainy days in late April and early May, cedar trees infected with the cedar-apple rust fungus will develop bright orange, gelatinous galls.

Cedar-apple rust is an interesting disease. It requires both an apple and cedar or juniper to complete its life cycle. On the cedar, the fungus produces reddish-brown galls that are up to golf-ball size on young twigs. During wet weather these galls swell and begin to push out bright orange gelatinous tubular structures. Wind carries fungal spores from these gelatinous structures to susceptible apple or crabapple cultivars.

Infection occurs when these spores land on a susceptible apple cultivar and moist conditions prevail. Small, yellow spots begin to appear on the upper leaf surface shortly after bloom. Spots gradually enlarge and become a bright yellow-orange color. These brightly colored spots make the disease easy to identify on leaves.

Heavily infected leaves may drop prematurely. In late summer small tube-like structures develop on the underside of the apple leaves. Spores are released from these structures and are blown by wind back to susceptible cedars or junipers, completing the disease cycle.

If you have followed along with this cycle, you might immediately think that a good way to break it would be to avoid planting susceptible hosts next to each other. Unfortunately, this is often impractical, because the fungal spores can travel as far as two miles.

Cedar-apple rust generally does little damage to cedars or junipers. In many cases, the disease is not noticeable except in the spring when the galls are producing the bright orange spore horns. If the disease is very severe, however, twig dieback can occur. Rust galls on small cedars and junipers can be pruned out in late winter or early spring (by April 1).

If you do not grow apples this is not really a problem on cedar. The galls can be pruned off but also can be left on either way it does not effect the health of the cedar.