Q: We have a lovely blue spruce outside our front window. It is about 20-25
feet tall now, and for the past 2 years several of the mid-height branches
have died. First the needles turned brown, and then they fell off. Nearby
branches are all right, though. What is happening?
A: It depends on where the brown needles are on the branches as to whether or not you possibly have a problem. If they're a couple feet toward the interior of the tree, it's likely the normal needle-cast that evergreens do in late summer/early fall.
If the brown needles are all the way to the tips, then you may have a canker disease, specifically Valsa (a.k.a. cytospora).
If you do have canker, you've got a tough row to hoe as there is no known "cure". Typically, canker starts at the bottom of the tree and works its way up, so your description of the branches half way up the tree being affected is unusual. Canker enters a tree through wounds, and usually wounds occur near the bottom.
Wounds include those made by pruning, and quite often are the result of running the lawnmower around the bottom (this can create hundreds of wounds in a very short time).
To try to determine if you have canker, inspect the dead and dying branches. You should find a bluish-white substance on them, and even limbs below them. This is the tree's sap, which oozes out of the branches as a result of the canker disease (be careful not to confuse sap with bird droppings!).
The sap carries the disease spores to the outside, where they can be spread via wind, rainsplash, birds, bugs, and people.
If you find this, carefully remove the diseased-looking branches. Prune only during dry weather (remember, rainsplash helps spread the disease), and sterilize the pruning tool as often as possible, ideally between each cut.
A simple aerosol disinfectant will work fine. Fertilization will help increase the tree's overall vigor, which may help it defend itself against the disease's progress.
Chemical sprays are not that effective, although injection with a systemic fungicide can help suppress the disease. You should check with a local arborist or two and ask them to inspect the tree to see if this actually is your problem, and if so, whether it's too far along to warrant treating.
Keep in mind that a couple other things can cause browning needles, including spidermites and spruce galls. It could be as simple as the branches just being broken. This is another reason to ask an arborist to check your tree, to diagnose the actual problem. You can also do some investigation at the Ohio State University's FactSheet website.
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