Looks like flicker going after larvae from here, maybe some squirrel help on the bottom pic. Maybe clearwing infestation, too hard to tell from 2000 km away. Maybe the stress from too little snow and too much heat?

Larvae suggested as food for flickers may be carpenterworm judging from the size of the holes and shape of the swelling. I also thought "squirrel" in the bottom picture - may have feeding on callus around the wound during a shortage of other forage.
hortster

Thanks. I've never seen any Flickers around here but that doesn't mean they aren't here. Last year we did have some insects but were advised to spray. We did that several times and thought we had it under control. Marg

Black locust, right?
Don't think it's sapsuckers - and the bottom one said 'squirrel' to me, too.
Top two photos look like what I see with some regularity on young Robinia here - I always figured it was borer damage and the tree's attempts to compartmentalize and overgrow.

I wouldn't worry. Robinias have all kinds of borers that do this and the trees still grow to maturity. Leaf miners in the leaves, small brownish beetles that cause leaf drop in July, borers that infect every part. The tree will grow several tops, each in turn dying. You also usually find these trees as twins, that is, 2 trees develop and grow side by side until one falls. Not to worry, when something happens to it, the ground erupts in 100 new trees that grow over your head in 2 years.

Did you plant these? The small trees are used extensively for fence posts around here. The flowers are a source of very light colored honey, but the fragility of the raceme of white flowers in May means you don't get a honey crop from Black Locust every year. "Locust Week", when the trees are in bloom, also tends to be a time when spring storms blow the flowers off the tree.

IIRC they were introduced into California by the Italians in ~1860s, have since naturalized and are quite the bother where they grow thick. Hereabouts last year I spent two weekends and three+ chains on a project thinning out ~1 ac. Not a bad wildlife tree but I don't care for the looks, personally. If it has established it may outgrow any infestation, as Dzitmoidonc indicates.

Like someone said, flicker/woodpecker damage going after the wood-borers that are so common on B locusts.

Robinias have all kinds of borers .... Leaf miners in the leaves ... small brownish beetles that cause leaf drop ... borers that infect every part. The tree will grow several tops, each in turn dying. ... 2 trees develop and grow side by side until one falls. Not to worry, when something happens to it, the ground erupts in 100 new trees that grow over your head in 2 years.

===>> and what exactly is the upside to this monstrosity??? .... lol

heck.. i would recommend a maple of this piece of carp ... lol

get rid of it ... and treat the cut stump with RU or stump killer.. and spend the rest of your life trying to kill all the suckers that pop up ... or better yet.. move the horse fence .. and let the horse kill it ... [though i suspect with the thorns.. even the horse wont like it]

ken

Ken, the spines on the main trunk are absent. One upside. The fact that the leaves turn orange/brown in July from the beetles' feeding on them means the sunlight can then reach your other plants. The bark falls off in large pieces so they can be used for orchids. The dead parts make excellent homes for carpenter ants, in case you want to raise those kinds of ants. Finally, because of the way they lean as they grow, you can predict the direction they will fall in a few decades after planting. So, see, lots of good points to Robinia pseudoacacia!

They do make good long-lasting fenceposts - and good firewood, as well.
Much prefer them to the infinitely more thorny honeylocust - which rots away almost as fast as an untreated pine post.
Was eyeing a couple of big HLs down on the creekbank last weekend - much thornier than the one in the link below.

Here is a link that might be useful: {{gwi:326637}}

Definitely a decent wildlife tree, and the wood burns hot.

I have one with an 18.5 trunk circumference. It's struggling now, has been limbed a lot, nearly hollow and it still comes to life each spring and blooms with a heavenly scent. It's been home to black snakes,squirrels, feral cats, and God knows what else. I hung a greenman plaque on it because if it isn't a determined life force, I sure dunno what is. I have black locust fence still standing installed in 1935. It's starting to fail now and rot, but it still tells you how durable the wood is.

Marric, not saying you care about such-or that you don't, for that matter-but aren't these things on the invasive list in your area? Anywhere north of S Wisconsin, it seems they are not a part of the native flora. Maybe I'm mistaken, but I consider them invasive junk. I think Dz's post gets it about right!

+oM

Sorry for the delay in getting back to you. Thanks for all responses. We planted the trees several years ago. The trees have never suckered, perhaps because they are in an area that is mowed often. We also have maples and mountain ash in that area. Not to many trees survive here, we've lost 6 crabapples and several other maples. The remaining maples are struggling. I know that in some areas BL are on the invasive list but not here, I like the dappled shade and the fragrance you get from them.