May 21, 2013

Quince Rust on Junipers

Another rust disease in the cedar rust group, quince rust is the most likely to cause serious dieback on junipers.

With this disease the bright orange “galls” are actually just slightly swollen lesions on the stems. Widespread lesions can lead to significant browning of the branch tips as pictured above. Spores which spread from these galls in the spring infect the alternate hosts of quince, hawthorn, crabapple or apple tree leaves. On hawthorn trees this disease causes causes symptoms on the leaves, white fringes on the fruit and swellings and distortion of the branch tips.

As with  similar rust diseases separating the juniper from the alternate host (the further apart the better) can help keep this disease in check.

For lists of resistant varieties and fungicides labeled for managing this disease refer to the Disease Section of  Cornell Guidelines for Commercial Production and Maintenance of Trees and Shrubs.

May 14, 2013

Hawthorn Rust

Bright orange swellings can be seen at this time of year on some Eastern redcedars and other junipers.  After a rain those small, translucent-orange galls with gel-like projections appear.  These weird galls are caused by an intriguing fungus that needs two different host plants to live!

Hawthorn rust galls on Eastern redcedar.
Photo take in May, Onondaga County, NY.

Close up of galls. (Click for expanded view.)
Photo take in May, Monroe County, NY.

In the spring the orange masses expand after a rainfall and release  spores that can travel though the air and only infect the leaves of a hawthorn, apple tree or similar host (see below).  Then in the fall, from spots that formed on the hawthorn or apple leaves, spores are produced that can only infect a juniper/cedar.  The cycle continues in the spring when you can see new galls on the juniper/cedar.  Although a problem for apple growers this rust disease does not cause serious harm to the junipers.   There are other rusts that can cause problems with junipers such as quince rust.

In addition to the foliage of hawthorn and apples this disease can occasionally affect the leaves of affect crabapple, service berry or quince or pear.  However this disease does not affect any other evergreen tree species.  Only  redcedars and junipers can become infected.