Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Pot Marigold

  • Calendula officinalis
  • Disease (causal agent) Symptoms Survival of pathogen and effect of environment Comments on control
    Powdery mildew *
    (Podosphaera xanthii)
    White, powdery mildew fungus on surface of leaves and stems. More common on older leaves and older plants. Disease is favored by moderate temperatures and somewhat shaded conditions; however, powdery mildew may occur on lower leaves of plants in full sun. Spores (conidia) are windborne. Protect plants with a powdery mildew fungicide.
    Root rot *
    (Phytophthora spp.)
    Plants are stunted and somewhat chlorotic. Roots are rotted. Phytophthora spp. are present in many field soils. Favored by poor drainage, heavy soils, or overwatering. Plant on raised beds. Drench soil with an oomycete (water mold) specific fungicide.
    Smut
    (Entyloma calendulae)
    Circular to irregular (0.25 to 0.5 inch in diameter), greenish yellow to brownish spots, sometimes with a darker brown border. Spots are somewhat thickened and evident on both sides of the leaf. Spores are windborne or rainborne. Fungus survives on Calendula and Calendula refuse, and probably on other related hosts. Favored by rain and overhead irrigation. Avoid overhead irrigation. Protect foliage with mancozeb.
    Pot marigolds are also susceptible to Pythium root rot * (Pythium spp.), gray mold * (Botrytis cinerea), rust * (Puccinia melampodii), spotted wilt (Tomato spotted wilt virus), root knot nematode** (Meloidogyne spp.), aster yellows * (Aster yellows phytoplasma), mosaic (Cucumber mosaic virus), southern blight * (Sclerotium rolfsii), cottony rot * (Sclerotinia sclerotiorum), Alternaria leaf spot (Alternaria sp.), Charcoal root rot (Macrophomina phaseolina), stem rot * (Sclerotinia sclerotiorum), and Verticillium wilt * (Verticillium dahliae).
    * For additional information, see section on Key Diseases.
    ** For additional information, see section on Nematodes.
    Text Updated: 11/20