Hi Dave - We're planning to use it this year - a trial patch anyway. I have done a LOT of study on this, talked to many farmers including a Purshade rep. Sunscald is a major problem for us.
There is a lengthy discussion, with the Purshade rep and several large tomato growers at
www.producecommunity.com. No use to reiterate all the data here - you'll have to scroll down; the discussion was last Fall. All the folks are still there, I think, so go ahead and ask your questions. I'll check over there and join you. The thread is entitled "Shade Cloth over Tomatoes". The Purshade discussion starts about half way through the thread.
Our main worry is the white, (harmless) calcium residue that remains on the tomato. It needs to be washed off before packing. Large growers run tehm greenish through a conveyor wash line - with the soft brushes and all - but that's impossible for us. Hand washing tomatoes would be a nearly impossible burden in our operation as well, for various reasons.
Much of the discussion centers on that issue - no question about it preventing sunscald - great product. But that darn residue problem may be a killer for us - looks like pesticide residue!! You'll see that one smaller grower in Tennessee tested it last year and had to wash them individually before marketting!! He said you could wipe them with a damp cloth and get "most" of it.
It's been used in the orchard industry for a long time. Tomatoes more recently. There's an organic formulation and a standard - both completely non-toxic. You have to use a spray rig with the agitator running constantly to keep the calcium in suspension. Not easy with a backpack
Supply source -- Helena Chemical Co. Fairly cheap -$50 bucks for a 2-1/2 gal jug.
Jack
EDIT - I should also mention that Helena is planning to market the product under their own house brand - "Sombrero" -- pretty clever name, actually. JME