Marigold Plant Diseases

Marigolds are often used in Asian countries during religious ceremonies to decorate statues.

Marigolds are members of the daisy family. They grow to a height of 24 inches and have fern-like leaves. The flowers range in color from yellow to a deep red. Marigolds can be used as a bedding plant or can be kept indoors as a houseplant.

Botrytis Blight

Botrytis blight (Botrytis cinerea) is a fungal disease that affects all parts of the marigold except the roots. The optimal conditions for the fungus are cool and rainy conditions. The fungus appears as gray spores that are dust-like if a plant is heavily infected.

Oedema

Oedema is a condition that occurs if the roots of the marigold take in much more water than the plant can use. The water pressure then builds up in the mesophyll, which are the tissue cells inside the leaf, and forms blister-like areas on the underside of the leaf. This condition happens most frequently in later winter when the soil is very moist. The blisters turn brown and go hard and this then causes the leaves to turn yellow and eventually fall off.

Powdery Mildew

Powdery Mildew is a fungal disease that appears as a white powder on the surface of the leaves and flower. On indoor marigolds, this can happen anytime during the year; outside, it is most likely to be seen late in the growing season.

References

• Plant Disease Diagnostic Clinic at Cornell University: Marigold Disease Factsheet
• Plant Disease Diagnostic Clinic at Cornell University: Botrytis blight
• Plant Disease Diagnostic Clinic at Cornell University: Oedema
• Plant Disease Diagnostic Clinic at Cornell University: Powdery Mildew
• Royal Horticultural Society: Powdery Mildew
• Plant Cultures: Marigold