Purpleleaf Sandcherry - fungus?

Hello,
We planted a Purpleleaf Sandcherry three springs ago. Every summer since then it develops black (or dark) spots on the leaves. The leaves then turn to a pale red/yellowish and green colour. It's happened again this spring, but very early, right after it flowered. A local store recommended a fungicide last year, which we applied with no results. I've reapplied again last week, but it's getting worse.
Is there something I can do. It is planted at the side of the front porch, with sun most of the day. The downspout is near by, but there never appears to be excess water.
Any help would be great.
thanks
Chris
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You don't mention where you are, however Michael Dirr notes that 'All P. X CISTENA types in Zone 7b and 8 struggle and are almost defoliated by late summer. They are much better adapted in the northern climes.'
Dave

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spring,
again
porch,
appears
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I'm in Ottawa, Ontario, Canada.
They are sold at all of the local area garden centres, so i'd assume they're ok for this zone.

since
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It sounds like blackspot, which roses get, but I don't know if sandcherries are susceptible. But it does sound like some kind of fungus. If so, you have to remove all the infected leaves--the fungicide won't help what's already infected, they just help prevent further infection. Blackspot thrives in damp conditions, but again, I don't know if that's what you have.
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thank you

then
reapplied
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Probably not blackspot, but I do know that plum pox is a big problem in canada righ tnow, you might want to google it and see what you can find.
Toad
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