Eucalyptus in trouble

Hi, I have 2 eucalyptus trees growing in large pots in the garden. We've had them for about 4 or 5 years and they're now at least 8 feet tall, maybe even 10. They seemed to be doing well, bushing out & lots of new shoots, until a couple of months ago when all the lower leaves, including from new shoots, started drying out, going brown & looking dead. The top areas all look green. Anyone seen this or know how I can help them? I water them regularly in hot weather & occasionally feed them. We've repotted them once into larger 60lt pots - about a year or 2 ago. I've never pruned them which could well be the problem but the idea of pruning off the only green areas now seems risky. Any advice would be very appreciated!

 

Not sure, give the bark a scrape at the bottom and see if it is still green.

I'm wondering if they are dying up wards, if you get my meaning.

I think these have a
Limited life in pots any way.