Why does the top of one of my Green Giant Arborvitaes keep dying?

[Area Man]

My backyard has 6 Green Giant Arborvitaes that were planted in Spring, 2015. All is well except that one of them has twice now had an issue with the top portion of it dying off.

What you see in the attached photo also happened last year (I can't remember when; probably during the summer or fall). I cut off the obviously-dead portion last year, but here we are again, and it's dead ... again. It happened within the last couple weeks.

Can anyone tell me why this would be happening? The rest of the tree looks fine, and is growing. Should I cut it again? (Will it grow vertically afterward?) Should I just replace it?

 

[JeffGu]

They often do that during the hot, dry parts of the year. No idea why just the one tree is affected, but you might trim the dead stuff off, again, and try giving that one extra water. Every two weeks, if you soak the ground down at the base of the tree so it gets down a couple of feet, they usually stop doing that. They're naturally vigorous, with few insect and disease problems. I'd give it a chance. By this time next year, it might shape back up and look alright. Mine get a little of the dead foliage on them, from time to time, and they've all survived. A couple have taken on a bit different shape, but not unpleasant.

 

[Area Man]

OK, I'll try that. They're served by an irrigation system, but now that I think of it, I cut back about a week ago (after receiving a "Holy %#@&!" water bill). I thought they would still be getting plenty, though.

I thought I read somewhere that once you cut the leader, they won't grow vertically anymore. Sounds dubious to me, but I guess I'll find out.

Thank you!

 

[BC WetCoast]

When you cut the leader, the leader won't grow vertically, but the top branches will become the leaders, so instead of one, you may end up with 2 or more. The growth hormone is still produced by the tree and has to go somewhere.

Is your mulch just up to the root collar, or is it up the trunk. If it sits too high on the trunk it could cause some fungal problems.