Answer: Rust is recognizable by small orange blisters on the trunk, not necessarily by red or brown needles. There are so many reasons that a fir may have reddish brown needles that that symptom alone is not a reliable way to diagnose the problem. Some major causes are environmental -- firs are intolerant of salt spray (foliage will brown near salted roadways) and air pollution, and the foliage can sometimes be desiccated by dry winter winds in particularly windswept areas. Also, firs shed old needles annually. Before asuming the worst, I would suggest contacting a professional arborist to come look at your tree.
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