Cedar-Hawthorn Rust

Scientific Name: Gymnosporangium globosum

Cedar-Hawthorn Rust as its name indicates is a disease of two urban landscape trees. The disease has two life stages, one which occurs as rust spots on foliage and fruit of hawthorn and one that creates galls on juniper. The disease can be quite devastating to the appearance and health of hawthorn and treatment on this host is necessary to prevent infection. On juniper the galls may be unsightly when the orange spores are oozing out, but otherwise they can be easily removed from the infected trees.

Attacks: Hawthorn (Crataegus spp.), Juniper (Juniperous spp.)

What you will see:

• Yellow spots on the leaves of hawthorn
• Rust colored fingers on hawthorn fruits
• Big woody galls on juniper
• Orange finger-like goo coming out of galls

Life cycle:

• Spores are spread by wind
• Spores move from hawthorn to junipers in late summer or fall
• Spores overwinter on junipers
• Fungal galls form in the Spring on juniper species
• Spores can be spread to apple hosts within several miles
• Most infections occur within a few hundred yards
• New leaves are susceptible to infection

Cultural Management of Cedar-Hawthorn Rust

Cultural practices:

• Reduce moisture around foliage
  • Re-direct sprinkler heads so that irrigation does not hit foliage
• Don’t plant junipers near hawthorns
• Remove galls from infected junipers in the winter

Chemical treatments can effectively manage the disease. Ask your Consulting Arborist for details.