Maybe we should do a monthly feature of obscure fungal diseases to dread; this is fun . . . and informative! Just wanted to say thanks for posting about this -- even if no one has dealt with silver leaf before and so this doesn't lead to meaningful discussion that helps you in your situation, it was great to be exposed to silver leaf (er, not literally) so that if I ever see anything like this in our orchard I'll have an instant reference point. Please keep us posted with anything you find out.
As far as treatment, while I can't offer anything specific to silver leaf, and yes, the perpetual promotion of overall health can only help your trees weather whatever it turns out is ailing them (although I do wonder at times, if you're dealing with a bad pathogenic bacterial/fungal infection, and are concurrently applying holistic fatty acids, etc., specifically to promote biodiverse microbrial populations, are you ever inadvertently aiding "the enemy"?), with regards to our toughest fungal pathogen nuts to crack (fungal fruit rot diseases like bitter rot,
Marssonina, and perhaps a pathogenic fungal infection masquerading as apple measles), we have become interested in looking more specifically at harnessing 'beneficial' fungi to help turn the tide.
To that end, we applied Lalstop G46, a
Gliocladium catenulatum containing product, throughout the cooler early months of our spring season. Preliminary results have been great (to qualify this statement, this was the only major change to our usual practice/app lineup this spring, and it was a normal spring, as far as plethora of potential infection events: our trees are the "cleanest" they've ever looked at this point of the season (although, interestingly, with the exception of Cedar Apple Rust, which is in more evidence on our fruitlets, but less on our leaves, than usual). We have an occasional spot of
Glomerella in evidence on leaves, but otherwise, nothing like the usual smorgasbord of fungal leaf spots that have typically piled depressingly on to our foliage as early as petal fall. The G46 fungi can't take the heat, so we've stopped applying it for the season and will move on to applying a new-to-us
Pseudomonas containing product (Howler, big organic ag at its finest, but we like the biology behind it). We'll keep updating our separate threads regarding apple measles and beneficial fungi hopes as opportunity arises.
Obviously, the Lalstop G46 isn't labeled for silver leaf, but just wanted to highlight it as a perhaps helpful example of at least trying to think outside the box a bit with some of the trickiest fungal pathogens we have to deal with. Hopefully, your issue will turn out to be something more understood and manageable! Good luck and thanks again.
Kordick Family FarmWestfield, NC
Zone 7a