I have a mature staghorn sumac in my yard. It has a south-facing exposure, shallow soil with regular irrigation. I esitmate the tree's age to be at least 17 years old. It appear to be trying to die. Last year the tree was fully leafed out. This spring it showed one dead branch (major) and two minor dead branches. The leaf clusters are only about 1/3 their normal size and appear to have stopped enlarging. There is a wound or canker on one limb that has removed the bark and is weeping slightly. there are no conks and no borer holes. There are fewer suckers than last year. Could this be due to the tree's age or is some disease process going on?
I don't have a huge experience with Rhus typhina - StaghornSumac. I had one in the Fraser Valley that died after a wet, cold winter. Many others in this area seem to suffer the same fate. I don't know what the rainfall is in Redmond but these plants prefer dry, well drained conditions in my experience. Quit the irrigation, I can'tmagine that it would need much or any. Also, these plants don't seem to be long lived even where they thrive. Your plant may have just gone past it's best-before date. They sucker readily, perhaps you can find one in your neighbourhood & underplant it this fall in case the existing one dies.
Yes, probably something going on beneath the soil. Partial die-back implies a pathogenic agent being at work.
Thank all of you who replied to my post about the DSS. I will observe the tree next spring and look for any signs of life. If none, it's a goner. Besides, I am tired of pulling up a million suckers each year. It's replacement will be a small tree that is a lot tidier in its habits, but I will miss the sculptural form and autumn color that the sumac provided.
