Hi Master Gardeners, I recently noticed a strange orange growth on a couple of branches of a juniper in my front yard. Any idea what it could be? How should I deal with it? Thanks.
Thank you for contacting the Toronto Master Gardeners.
The strange growth on your juniper trees could be either pear-trellis rust or cedar-apple rust disease caused by the plant pathogen Gymnosporangium sabinae or Gymnosporangium juniperi-virginianae respectively. These fungi spread from junipers/cedars to apple/pear trees (including crabapples) and then back to junipers. Juniper is actually the winter host of this fungus.
The fungus usually becomes active on junipers during a warm wet spring. In the spring following rain the galls produce large orangey tendrils full of spores, which can blow around for quite a distance and spread the disease. Hard brown galls form at the ends of the branches in the summer. Any close neighbours who have apple or pear trees may be in trouble. Although the presence of these galls on your junipers may be unsightly they rarely cause significant damage to the juniper. There is very little that can be done in Toronto to stop or control this disease. The only action you can take is to consider replacing the junipers and replant with a variety that is resistant to rust. You can find Junipers resistant to rust here.
One of our srchived posts titled Pear trellis rust gives more information on this disease.
This website discusses the life cyle of cedar-apple rust and you can find information on pear-trellis rust here.