A few leaves at the bottom of my heirloom chrysanthemums, (Cathy's Rust), are turning yellow with dark areas. They had a lot of aphids at the tops of the stems several weeks ago, but I pinched those parts of the stem off and the aphids now seem to be gone. The plants have really multiplied since I planted them last summer. What could be causing the leaves to turn yellow? What might prevent this problem? Thank you.
Has it been dry over there? Does the soil around it feel dry to the touch? How many leaves are we talking about? A handful? Half of the bush? Have the stems been damaged? Are the veins also turning yellow? Do you see any leaf deformation, leaf wilting or leaf twisting?