This is the second time since I planted a Black Hills Soruce 10 years ago that it has developed a brown, rusty color. The first time it was as about 5 years old and had great growth and shape but suddenly started to appear rusty looking. I thought it was dying and would need to remove it. Luckily I didn’t and now it is about 18 feet with thick growth branches but again turning brown/rusty looking. Is it a fungus? Will it survive again? What can I do to help it, if anything? Thank you.