"How long does it have to be dry for dormant spray to be effective?" - "Those of you local will understand the reason for the question"
You've got me smiling here... With "lime sulfur and/or spray oil" (the same combination I use) - my 'guess' is the-longer-the-better! I assume the sulfur 'burns' the offending lichens / mosses, and the oil smothers the hibernating crawlers? I figure - the dryer it stays - the more gets adsorbed...
Maybe we'll get a dry stretch pretty soon..? We're sure owed one! 'My question' has always been: the instructions tell you to spray with "dry and increasingly warm temperatures"... That isn't how it happens - the dryer - the colder! Maybe that's their way of dodging responsibility if it 'doesn't work?' "Well, it got colder, not warmer..." I've read that extreme cold
might 'drive it' into the plant. --- I don't know that I've ever witnessed such extreme cold
around here (Willamette / Tualatin Valley), and know I've never detected any damage from this combination of spray - though I've also read 'we' shouldn't 'mix it' like that
I'd watch for some dry stuff - they seem to be able to predict dry and cold real well - then hit 'em good!