We recently came across a little juniper shrub in weakened condition in a garden with no visible signs of what the cause was. We suspected juniper-hawthorn rust but there was a young hawthorn tree close by that looked healthy and vibrant with no signs of stress. A little research and a few clues from the home owner led us to a few details that confirmed our suspicion. Most prominently, the presence of a large gall on the little juniper that had recently been removed but the home owner still had available to see. A clear indication of rust.
We’re still early in the season and it’s likely too early to see any yellowing spots that would be expected on the hawthorn leaves. Juniper-hawthorn rust also has alternate hosts such as mountain ash and apple and both were growing in close proximity to the juniper. Interestingly, we had just had a conversation with the home owner about the older of the apple trees and how it did not produce well the last few years. They attributed this to having pruned it back significantly hard for more than one year possibly too late in the spring after it had bloomed, but given the clues in the yard, alternatively it may be possible this older tree is also being affected by the rust.
It will be interesting to watch as the season progresses. For more information on juniper-hawthorn rust I found this article helpful: