mdo, I can shed a little light on this: With the Emamectin Benzoate-style treatments available now, tradenamed Tree-age (The 'a' has the two little umlauts or whatever they're called above it, and the word is pronounced like the word triage), it is reasonable to expect two solid years of control from a single treatment, and quite possibly three years. For high-value trees like yours, this seems like a reasonable thing to do. Alternatively, the Imidacloprid insecticides will give a single year's control but are easier to apply. So even that's not a crazy thing to do. Environmentally speaking, either one of these methods is fairly low risk to surrounding organisms, being either injected straight into the trunk, or spread on the ground and soaked in via watering or rainfall, depending on which chemistry you reach for. The other half of your question I can answer too: What seems to happen with EAB is similar to other exotic insect invasions-there is a ramping up period, a period of overwhelming infestation, and then, just as you'd probably expect,a leveling off period after the insects have killed most of their hosts. So if you do happen to save yours during the hot time, you would still need to treat to have the surety of protecting the trees, but overall pressure would level off a great deal. These two lines of thought are straight out of very recent arborist's convention/seminars, so they are up to date. The relevance of this winter's cold temps was also a hot topic (Buh dum bum), but in reality, most thought is that while some of the less-deeply positioned larvae may indeed be killed, EAB has two larval forms and one of them is positioned deeper into the trunk, likely meaning the weather will have fairly little impact one way or the other. We can always hope though! +oM

I don't think those are emerald ash borer holes, but the fact they're suckering near those holes are ominous. I have seen them and lost a MAGNIFICENT ash to it. (s.e. Ohio) The EAB tunnels shallow galleries of mazes directly under the bark, and effectively just girdle a tree to death. They do not tunnel deeply and you should be able to identify the galleries if you'll peel back the loose bark of one of the affected dead/dying limbs if you can reach one. You'll see a limb here and there going first and in the course of a couple years it's apparent the tree is a goner whilst the wood of the main truck will look totally beautiful when it is felled. Sometimes cavity dwelling birds will start holes like that and change their mind and go elsewhere. I can't tell the girth of your tree from the pic, nor how high up the tree it is located. After I lost my beautiful ash, it became apparent to me that those in my small woodlot are gonna be dead men walking, and I will not release neonicotinoides into the environment on a scale large enough to save wildlings. It would have to be a particularly special tree to even consider it and it really concerns me to see this class of chemical touted to homeowners as a fix for this epidemic.

I have just had my power restored after 5 days in the dark due to branches from a neighbor's ash tree hitting the lines (there were 250,000 people in SE Michigan without power early this week). This darn ash has splits in its bark (going upwards) some as deep as 1/2 inch (on a tree whose diameter is only about a foot) and stretching 6-10 inches. It seems to have holes all over the place (I'm assuming from insects of whatever sort) and though it has some bare branches (mostly due to upper shading by the tree) it seems happy as can be. My nieghbor attributes its resistance to the EAB to his occasional spilling of battery acid (among other things) near the trunk (behind his garage). Personally we'd like to see it succumb to EAB or something as it shades a large portion of where I put my raised beds for veggies (it was smaller back then). So, the moral of the story is wish for the tree to die, curse it regularily and contemplate its demise regularily and it will survive, thrive and be just fine. ~Chills

Mountain ash are very prone to borers that kill the tree in this fashion. Barring some chemical interference like lawn fertilizers or weed killers, I would suspect that the tree may have a borer. Check around the base of the tree for holes in the 1/4 inch range in size. This will tell you what has happened.