Peculiar Fungus on my Junipers

(Question)

I’m phoning for some advice on a very peculiar fungus growing on my junipers which is rusty in colour.  It started out as little pebbly dots.

 

 

(Answer)

The strange growth on your juniper trees sounds very much like a cedar rust disease (Gymnosporangium spp.), which is indeed a fungus that spreads from junipers 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.  This may not be realistic in your case, as it sounds like you have several junipers.

For further reading visit:

https://www.omafra.gov.on.ca/english/crops/facts/cedarap.htm

https://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1036/EPP-7611web.pdf