Holy Bejesus!! So sorry to see your tree take such a hit.
Saw very similar situation with the Hinoki and Junipers my brother in law ‘gave to us’, along with six other trees with a plethora of dead branches, cedar apple rust, bugs, weeds and other horticultural issues. Seven absolute work bombs… but great challenges all the same! Three were Junipers. All healthy today.
The great news is Junipers have a will to live unlike any tree we have worked on. Itoigawa is no different than Kishu, Shimpaku or any of the others we’ve worked with in this respect. Just have to come up with the thing that will let the tree turn the corner.
My thoughts picked up on something while reviewing the thread. Certainly could be wrong. I think there is a lens effect going on.
Many times the internal root ball has materials that are decayed and more roots. (Also when when the tree is tied down the area gets more compact. The result is internal root ball has a less interstitial spaces for gas/fluid exchange and holds on to water longer compared to new media .
The addition of more porous media around the root ball sets the lens effect. Outside media, where only a few roots exist, gets super gas/fluid exchange. On the other hand, the core rootball area has less gas/fluid exchange. Water flows much slower in the area, which stagnates and roots become unhappy.
… and watering needs become extremely hard to guage. Resulting in underwatering or overwatering issues.
It is why do not like HBR as a rote response because this issue doesn’t always show up. Imho this technique depends on a person being able to accurately compare the existing media’s fluid/gas exchange to the new media. Certainly it’s different in all cases, but sometimes, the difference is so much, issues show up. But enough different to cause big issues.
The best solution we have found is to drill the core, especially angling inward and under the shin. We do this on just about every repot that seems iffy. Have never lost a tree we drilled. Nowadays mostly use a concrete impact drill bit (broader tip) but not always, and just let the drill find its way around the roots. (A friend of mine uses a steel rod instead of a drill.)
Also may want to chock up one side of the pot for awhile to keep things on the dry side.
Personally would leave it at that, no root enhancer, no fertilizer for awhile, just water. Don’t want to inadvertently compound the issue.
If one wants to also lean on a chemical solution too, would use hydrogen peroxide 3% and flush after 10 minutes.
The other go to is ZeroTol - very effective for root issues but one needs to be knowledgeable when using this product. Please read Michael Hagedorn’s blog about its use.
Also please read this SDS. Store properly - it is a potent oxidizer.
Just my thoughts. In any event sincerely hope the tree pulls out of this decline.
Best
DSD sends
