Echinacea is one tough perennial plant but it is susceptible to fungal diseases on the leaves especially after lots of rain. Try to keep the foliage dry. The other reason the foliage could turn brown is root damage from underground rodents. Do you have moles or voles? You can clip off the worst of the brown sections to give the plant a fresh start. If the brown leaves return then uproot and destroy the plant so the infection does not spread. Keep growing, Marianne Binetti