undiluted lime sulfur -- any guides on when&how this can be dangerous to our trees?

[SU2]

I stuck to hydrogen peroxide for bark & deadwood, + a torch to burnish deadwood, but am back to using lime sulfur on the deadwood as well. I've found I'm increasingly using larger & larger amounts, usually in-context of "overshooting" the area I'm trying to work on (IE if a bougainvillea has a large shari I won't just apply to the shari, but to the 'lip' of living bark around it, I do this because of how bad die-back can be on newly-acquired, larger Bougies but same logic applies to other cases) After hearing some anecdote (think it was that Pall did it), I've tried my first 'test areas' of using LS on the dark, previously-underground rootage you'd see on a Ficus whose soil-height was just reduced an inch (in fact I only did some of them, and many 'tiger striped', so I could kinda test out how well it works -- I saw a pic of him using this strategy on some Pine's finer surface-roots, both enhancing aesthetics & widening the 'spread' at soil-surface of the specimen)

I got used to using my favorite spray (hydro perox) like it simply cannot hurt anything, after having done some tests years back where I tried and failed to kill some trees by watering w/ nothing except hydro for days (they shed their leaves in a week or two but didn't die) so use it verrrry liberally and, lately, am finding my LS usage to be falling into a similar pattern... any & all advice on this would be greatly appreciated, sadly I'm low on 'throwaway' trees to test on these days, and have a whollllle lotta area I want to bleach (well, bleach / burn / bleach / burn, I alternate whenever it looks like it needs treatment, this has been reallllly effective in humid FL even Bougie hardwood can be preserved far more than most think.....the burnishing part is really key, it's great aesthetically but also - like 'shou sugi ban' techniques - imparts changes to the wood that realllly enhance its integrity so combining that with LS works awesome here!)

Thanks for any warnings on over-use of LS, heck maybe it's leaching into substrate simply because I used an ounce on a single tree the day of a rainstorm, am just uncertain and google is failing me for 'cheat sheets' (which I expected would be easy finds....FWIW I care most, species-wise, about BC's, Ficus, Bougie, Crape Myrtles, Red Maples for instance I have a 1yr old specimen that is just all deadwood like > 1/3rd its mass it takes a TON of LS to treat it, I haven't noticed ill-effect on anything yet but it's not growth season now so can't be sure I would notice..)

 

[Shibui]

There are many warnings not to get undiluted LS on bark or on the soil. Like you, I have often overpainted or dribbled some on the bark and occasionally spilled small amounts on the soil. So far the sky has not fallen or trees died but it does bleach the bark so can look pretty bad for a long time. I suspect that is the origin of the warning rather than physical harm to the tree.
LS on the soil could be a little more harmful. A few drops does not appear to hurt anything and the little that leaches down after watering does no more harm than the traditional winter dilute LS sprays and dips the Japanese bonsai masters love. I have seen one Bonsai today article showing a dead tree which was attributed to spraying undiluted LS over the whole tree and pot by mistake. One anecdote does not make it true but I would avoid letting large amounts get into the soil just in case.

 

[clem]

Previous summer, i applied pure lime sulfur on a japanese maple trunk cut horizontally in order to prevent the entry of germs. The pb is that it killed 3 out of 4 young shoots just below the cut, probably because the lime sulfur enterred inside the wood. So, from now on, i won't do it again, not even diluted. I'll only use healing mastic.

Another observation : I sprayed a lime sulfur solution diluted to 4% on the leaves of a japanese maple, to scare away an hypothetical insect or caterpillar that i suspected to eat the leaves, and i was surprised to see that it did not burn the fine and fragile leaves.

 

[SU2]

Previous summer, i applied pure lime sulfur on a japanese maple trunk cut horizontally in order to prevent the entry of germs. The pb is that it killed 3 out of 4 young shoots just below the cut, probably because the lime sulfur enterred inside the wood. So, from now on, i won't do it again, not even diluted. I'll only use healing mastic.

Another observation : I sprayed a lime sulfur solution diluted to 4% on the leaves of a japanese maple, to scare away an hypothetical insect or caterpillar that i suspected to eat the leaves, and i was surprised to see that it did not burn the fine and fragile leaves.

confused, sounds like you're saying you LS'd the chop-wound, but if that's the case there wouldn't have been lil buds (yet, unless you meant you cut it, waited, then applied? Though if that's the case I'd wonder at what use it'd have, after the wound was allowed to be exposed for any real amount of time...I kinda think of it as human tissue, lol, like when I make a deep cut into heartwood I spray with hydro perox and then LS very quickly, very little opportunity for anything to get-into my heartwood!)

 

[clem]

I do my JM big cuts in summer. It is the best time for me because the wounds close quicker, as the tree is very active, and there is no sap issue (no bleed, no withdraw). So i made an horizontal cut of the trunk in August (clip& grow) above 4 shoots on the same node. But the pure lime sulfur on the horizontal cut burned 3 of the 4 shoots a few days after application. I try to learn from my mistakes so i will never do this again. I now use an healing paste.

 

[SU2]

I do my JM big cuts in summer. It is the best time for me because the wounds close quicker, as the tree is very active, and there is no sap issue (no bleed, no withdraw). So i made an horizontal cut of the trunk in August (clip& grow) above 4 shoots on the same node. But the pure lime sulfur on the horizontal cut burned 3 of the 4 shoots a few days after application. I try to learn from my mistakes so i will never do this again. I now use an healing paste.

WOW!! Although I've seen (cannot link ) demos of a "slice" of a fresh tree-trunk (like, 2'+ thick) on a lab/demo table and they're basically straws in a sense. So...it's a question of "how much deadwood is 'insulating' the soft/wet/living/healthy heartwood from the LS you're about to apply?" then!

Would love to hear others' experiences, especially specie-specific stuff (anything on BC's is always appreciated ;D )

I have tried drowning Bougainvilleas with pure (well, grocery-store so 3% I think?) undiluted hydrogen peroxide, just using it instead-of water, it caused the specimen to drop its leaves but rebounded with a fresh flush and went back to normal (I swapped to pure water at onset of problem), this was in-testing-for-safety since hydro+toothbrush cleanings are all but required on a frequently watered FL garden!!

Will continue using hydro.perox on my open-wounds but will be even more liberal/aggressive to see if I can note any "uptake problems" where I see damage (and as you mention summertime is 'good' for such things but can be a double-edged sword, I think a better word than 'good' is simply 'faster' ;D )