What is this on my zinnia leaves?

This is a leaf spot caused by Alternaria blight. It is very common on zinnias. Retired UT Extension Agent Mike Dennison recommends some cultural practices to avoid disease and lists some fungicides you can use to help.

Related Videos:
Fungicides
Mixing and Applying Fungicide
Powdery Mildew on Zinnias

Related Resources:
Alternaria Blight of Zinnia
Zinnia - Alternaria Leaf Spot