Browning near the vein or brown and yellow blotches
Anytime you see these sorts of instances on your tree’s leaves, there’s a good chance that anthracnose has infected your tree. Anthracnose can cause early leaf drop if you’re not careful, so be extra cautious. If you are experiencing early detritus, then make sure to rake the infected leaves away from the tree. You can use pesticides and tree fertilizer to combat the infection, but that’s probably best left to an arborist.
Brown, wilted leaves falling after pruning
This is a disease particularly common in Oak trees called oak wilt. If you’re noticing this, feel free to strip back a tiny piece of bark and what lies underneath should tell you if you have a problem or not. What commonly happens is that you’ll see streaking under the bark on the body of the tree and usually happens when you’ve pruned too much.
Evergreen turning color, and then turning brown
Rhizophaera needle cast is a common occurrence in evergreen trees. This is an extremely dangerous infection that – if it goes untreated – can kill your trees over the course of a few years, so if you’re noticing it in any abundance, you need to get proactive about finding a solution. You need to prune out the worst branches immediately and then rake up and dispose of all the fallen needles first. It’s probably a good idea to call an arborist, who’ll be able to spread some fungicide around the tree to keep it from spreading. When mixed in with particular fertilizers and steady watering, the problem will eventually go away – but you need to stay persistent in order to save the tree, itself.
While there are some other infections out there, these are the three we’re most likely to see here in New England. And as always, if you have any concerns about your own ability to treat these diseases, you should contact a local, certified arborist immediately.