Pythium Root Rot in Poinsettias


Poinsettias (Euphorbia pulcherrima) are widely grown house plants, particularly popular at Christmastime, that can be vulnerable to root-attacking fungal pathogens. Pythium root rot is a disease that seeks out poinsettias as host plants. Avoid the loss of your prized indoor plant through careful care and familiarizing yourself with ways to recognize a pythium infection.


Vigorous plants have a much greater likelihood of avoiding attack or recovering from pythium root rot when compared to neglected and weakened poinsettia plants. Grow poinsettias in coarse textured potting mix instead of garden soil that may contain fungal pathogens. Provide a location that offers full sunlight; consider a sun-filled window that faces any direction other than north, recommends the Ohio State University Extension. Poinsettias thrive in daytime temperatures of 65 to 70 degrees Fahrenheit and cooler nighttime temperatures that remain above 60 degrees Fahrenheit. Extreme temperatures will injure your poinsettia.


Pythium root rot of poinsettias is caused by fungal pathogens of the pythium species, according to the Alabama Cooperative Extension System. Pythium root rot fungi develop in potted plants with consistently wet soil with poor drainage, in over-fertilized soil and certain pathogens prefer a temperature range of 50 to 86 degrees Fahrenheit.


Pythium root rot of poinsettias results in fluid-saturated roots and stem bases that turn brown as they decay, according to the Alabama Cooperative Extension System. Leaves often turn yellow and fall from the plant and premature flowering commonly occurs. When roots rot they are incapable of absorbing necessary nutrients and water. The destruction of root systems leads to plant death.

Natural Control

For natural control of pythium root rot on poinsettias, sanitize all tools and equipment that come into contact with your plants to prevent the spread of disease and infection. Use sterile potting mix and pots. Avoid waterlogged soil conditions. Remove and destroy infected plant parts and, when death occurs, remove and destroy the entire plant and its affected potting mix, according to the Alabama Cooperative Extension System.

Chemical Control

For chemical control of pythium root rot on poinsettia plants, utilize a fungicidal drench or spray your poinsettia foliage as a preventive measure. Apply a fungicide with the active ingredient etridiazole, fosetyl-A1 or mefenoxam, according to the Alabama Cooperative Extension System. Contact a licensed professional or your local county extension agent for assistance.

Keywords: poinsettia plant fungi, poinsettia pythium rot, poinsettia root rot

About this Author

Tarah Damask's writing career, beginning in 2003, includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum, and articles for eHow. She has a love for words and is an avid observer. Damask holds a Master of Arts in English and creative writing from the University of North Texas.