What is that orange ball on your cedar tree, or those red spots on your apple or pear tree? It is cedar-apple rust or some other related Gymnosporangium fungus.
Cedar-apple rusts (or other closely related rusts) occur on cedar trees as well as an alternate host tree. These alternate hosts include apple, crabapple, pears, quince, serviceberry, and a few others. This rust will appear on a juniper tree after it is infected and will germinate to a gelatinous orange blob 18 months after appearing. Eventually, these blobs will dry, turn brown, and fall off. The spores from a juniper will infect one of the alternate hosts in the Rosaceae family (apple, pear, etc.), and the leaves of an infected tree will have yellow spots shortly after bloom. Heavy rains within the first few weeks of bud break will cause the fungal infection to spread and be much worse. These yellow spots turn orange and form bumps on the leaf surface which ooze spores and infect junipers. Early defoliation can occur on heavily affected trees. This disease does not usually kill trees, but may require treatment if on edible fruit trees or for aesthetics.
- Remove galls from cedar trees by hand
- Spray preventative fungicides on fruit trees during leaf emergence
- Avoid mixing cedars and trees in the Rosaceae family
- Plant resistant fruit varieties
If you have questions about your tree please contact us.