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How to Manage Pests

UC Pest Management Guidelines


Floriculture and Ornamental Nurseries

Pot Marigold (Calendula officinalis)

Disease Control Outlines

(Reviewed 3/09, updated 3/09)

In this Guideline:


Disease (causal agent) Symptoms Survival of pathogen and effect of environment Comments on control
Powdery mildew
(Erysiphe cichoracearum, Sphaerotheca fuliginea)
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. more info *
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 mefenoxam. more info *
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 wind 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 (Sclerotina sclerotiorum), and Verticillium wilt * (Verticillium dahliae).
* For additional information, see section on Key Diseases.
** For additional information, see section on Nematodes.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
S. T. Koike, UC Cooperative Extension Monterey County
C. A. Wilen, UC IPM Program, UC Cooperative Extension San Diego County
Acknowledgment for contributions to Diseases:
R. D. Raabe, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
A. H. McCain, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside

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