Septoria leaf spot
IDENTIFICATION — Septoria leaf spot is a common fungal disease that can affect black-eyed Susans. It begins with brown-black spots on the leaves then progresses to where the leaves may turn completely brown and fall off. Symptoms usually appear on lower leaves first.
CONTROL — This disease is tricky to get rid of but won’t kill your plants. Septoria spores are spread by water droplets, so watering at the base of the plant will reduce the spread. Rake up diseased leaves and burn or bury them. Don’t put them in the compost pile.
You can apply fungicides before any symptoms appear, but keeping the area clean will keep the plants looking better next year.