Can I attempt to diagnose a diseased tree online? We’re getting more brown spots on our grand fir and I would like to try to figure out what is wrong.
You can attempt it, but you will not know for certain based solely on a comparison of symptoms. You can certainly get an idea of what the potential problems could be. Try the Pacific Northwest Plant Disease Management Handbook online—it has excellent photos. Search for fir.
There are several possibilities with brown spots as symptoms, especially:
*needle casts (there are 3 kinds)
*rust
*web blight
*current season needle necrosis
*shoot blight
*Grovesillea canker
*interior needle blight
The best way to diagnose a problem is to bring photos of the affected tree along with samples (if you can reach them) to your local county extension agent or Master Gardener diagnostic clinic.