Cedar-Apple Rust on Arborvitae: Orange Jelly Horns in Spring

Identifying Cedar-Apple Rust on a Small Cedar/Arborvitae

A small cedar (possibly arborvitae) has inch-sized, brownish-purple, sectioned nodules with bright yellow spikes appearing in spring. The owner asks if they're insects and if they're harmful.

Diagnosis

This is cedar-apple rust. The "jelly horns" are the spring fruiting bodies releasing spores to apple/crabapple hosts. On cedars, it's cosmetic—galls drop in a couple of years. On apples, it causes leaf spots and fruit damage.

Key Points

• Requires two hosts: cedar/juniper and apple family.
• No control needed on cedar.
• If you have apples, plant resistant varieties or fungicide spray.

Your cedar is fine; the weird growths are just the fungus reproducing.