In article , "Andy"
wrote:

Dear All:

Last year I battled applescab in our crabapple tree all summer. My
understanding was that I had not sprayed the tree with fungicide early
enough, in what was a very humid spring here in Rhode Island. I don't wat
to repeat the same mistake this year. Does anyone know 1) what I should
spray on the tree? and 2) when I should spray it?

Thanks,

Andy



There are a number of fungicidal treatments available that are effective
against scab. The three (organic) types I know about are fixed coppers,
micronized sulfurs, and calcium polysufides (lime sulfur). It's
generally best to use a sticker-spreader with any of these. A dormant
spray may be helpful but it's generally best to get any of them on at
the green tip stage (just beginning to bud). Avoid spraying while
blooming. Thereafter you should try to spray when conditions for
infection are present, i.e. just before rain (or even fog) when
temperatures are above 40 degrees F.
Some of the non-organic fungicides have the advantage of "kick-back",
they eradicate infection already underway, which the organics are not
effective at.
Another big help keeping scab in check is removing all dead leaves in
the fall (the organism overwinters in them).