Q.Spots on black eye susan
How do you prevent spots from coming on leaves? What is the name of an insecticide to use to prevent them? Every year the plant gets brown spots.
There are a few different fungus or diseases that can be found on Rudbeckia or Black Eyed Susan's.
Thinning the plantings to allow air circulation and when watering not splashing the plants leafs can help control the spores.
Chemical treatments are specific to the type of fungus that the plants are infected with.
Here is a great article and link that will help you.