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
but did not see any solutions posted.
TIA for any advice