Please look at the photos and let me know if there's any more I can do to help it heal up.
re the lemon tree
All of those smaller branches which are dead and/or dying inside the canopy, can be removed. The sooner the better. They are preventing good air circulation inside the canopy, which is possibly one of the main factors contributing to the problem. I notice too that some branches have been pruned or have fallen off leaving small stubs sticking out. These are a great way for fungal problems to enter your tree
. So i'd go at the tree
with a clean, sharp pair of secateurs and loppers and clean out the rubbish inside the canopy. Cut branches off almost flush with the main branch so the tree
can heal over it. Don't be afraid to go a bit berserk with the loppers. The tree
will handle it. Dispose of the cuttings, don't use them in compost. Clean your tools afterward/during the operation in methylated spirit.
What is the problem with the tree
BTW? Is it a fungal problem? It looks like it is fungal based but it's not something i've seen before. If it was my tree
i think i'd skeletonize it and clean all the growth out. There may even be a few main limbs i'd consider taking out, but anyway...
Another thing the tree
may need afterwards is some decent mulch and a feed. Not right up to the trunk, keep the mulch back about 2 feet from the trunk and extend it out past the dripline. Depending on where you are you may get a new flush of growth thru Autumn.