July 31, 2015
- Cedar–apple rust, Gymnosporangium juniperi-virginianae
- Cedar-hawthorn-rust, G. globosum
- Cedar-quince rust, G. clavipes
These fungi require two different hosts to complete their development: an evergreen host (mainly junipers) and a rosaceous host.
Rosaceous hosts of rusts
Symptoms on junipers
How it’s spread
These rusts overwinter on their evergreen hosts and produce jelly-like masses of orange telia from perennial galls during warm, wet weather in spring. Telia give rise to a different type of airborne spore that infects members of the rose family.
Symptoms on rosaceous hosts
Galls on junipers can be pruned off and destroyed before spore horns develop, but usually, only rosaceous hosts need protective fungicides. Apply labeled fungicides to broadleaf hosts as orange telial horns are first visible on juniper and repeat at several week intervals. Select resistant cultivars where possible when making new or replacement plantings.
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