Calendula sp. may get one or more of the following diseases. Calendula smut that causes brown round spots. Alternaria leaf spot that causes small reddish-purple spots. Aster yellows (caused by a phytoplasma rather than fungus or bacterium and is transferred from plant to plant by insects) causes stunting, yellowish-green foliage and flowers followed by death of plant. Eradicate plant as soon as symptoms noticed. Powdery mildew may also occur. Fungicides (except for aster yellows) and sanitation are important.
Written by James Schuster, Extension Educator, Horticulture, and reviewed by Bruce Paulsrud, Extension Specialist, Pesticide Applicator Training and Plant Pathology, University of Illinois at Urbana-Champaign.