This happened to my neighbor here in zone 5, as well, last year. They pruned it drastically and it leafed out and budded well. This year the tree is recovering beautifully, and has no dead branches whatsoever, so it can happen. I wish you luck with your decision and the outcome.

Maybe it froze.

Just as a matter of interest....what is the side of the tree that lost leaves? N, S, E or W?

It is conceivable that HL is not quite sufficiently winter-hardy for this very cold location. There is a type of canker that can afflict HL and which is active at relatively low temperatures, called Thyronectria canker, which can kill large portions of the plant. This disease presents as sunken areas on the trunk or at branch junctions. Just throwing that out there as one possibility.

+om

The dead side is facing east and not protected at all from my house and the neighbor. After close inspection a few of the 'dead' branches have very small buds that look dried up, dry and dark compared to new growth of the same size on the healthy side of the tree. We had very warm weather here in March followed by a few weeks of frost so maybe parts of it froze. Should we prune it now, or wait till fall?

Thanks to all of you for your comments and suggestions. I have never seen any type of worm of it but will check closely for canker worms.

Laurie B The canker wisconsintom refers to is a bacterial or fungal (usually) infection of the bark and underlying wood. It has nothing to do with worms. Canker does not seem the most likely explanation in any case.With your description, it seems very likely that the buds on the eastern, sunny side of the tree had started to swell and were then killed by low temperatures. You can wait a few more weeks to see if new buds emerge or prune back now. Locusts are usually quite vigorous so your tree should fill in over the summer.

Right^. I mentioned the canker disease (not insect) only because it is a threat to HL wherever it is grown. I agree with Maine that this is an environmental issue, not one of pathology or insect damage. You may be on the edge of this plants hardiness rating period, and as such, these things can happen. Throw in the possibility of a weakened plant due to prior drought or some other situation, and every plant doesn't make it every time.

+oM

Thanks to everyone for all your advice. I really appreciate it. I am going to wait a few more weeks and then prune it. I will leave a few bare branches in case they fill out again next year (my fingers are crossed)!

Laurie B If no new buds emerge within the next few weeks, i would not leave any bare branches until next spring. Such Lazuras-like ressurection after a full year is asking way too much of any tree. Dead branches can be a prime entry for insects and infection, so cutting out any dead stuff is important. Scrape away a bit of the bark right now on any of the bare branches. If you see green cambium, it's worth waiting a few weeks. If there is none, you might as well prune back to where you do find green cambium now.

Honeylocust has no "buds" to speak of, they being hidden from view. But Maine's advice still holds-that you will know sooner than next year as to viability of these branches, and that leaving them on that long is not likely to work out satisfactorily. Sorry.

+oM