Brown / black spots on Rudebeckia

Hi,
Every year I get black spots on the leaves of Rudebeckia plants. Some of the leaves are turning yellow. I am presuming that these are effects of insects/fungi and I have been spraying them with 'Ortho Insect and disease control - Formula III'. I am not too sure if it is very effective. The plants seem to thrive and flower every year though the leaves turn yellow and eventually dark brown. Is there something else that can be done? I ggogle and found someone else had the samne problem
http://www.icangarden.ca/forum.cfm?task=viewthread&chatthreadidd70
but did not see any solutions posted.
TIA for any advice
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It's just something that happens to Rudbeckia. Worse in some years than others. It only upsets people, but doesn't kill the plant. Stop spraying chemicals on them without having any idea what the cause is. Those chemicals have never been, and never will be proven to be safe.
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