Black Root Rot in Greenhouse Flowers


Black root rot is a widespread fungal disease that can cause a large amount of damage to flowers in the greenhouse. Fuchsia, vincas, petunias, geraniums and poinsettias are among the greenhouse plants that are susceptible to the disease. The fungus that causes black root rot can live in the soil for years. It is easily spread when apparently healthy seedlings and other greenhouse bedding plants are transferred to the garden because infected symptoms do not show up on the infected plants until they undergo stress.


Black root rot starts attacking a stressed flower at the middle of the root. Cankers can be seen when the dirt is washed away. As the rot continues to attack the plant, symptoms will appear above the soil. The growth of the flower can be stunted. Eventually the foliage will turn yellow, wilt and die.


The fungus Thielaviopsis basicola causes black root rot. It lives in the soil and can go undetected for years. The spores of the fungus can also be carried by wind through the air. It can infect a healthy flower plant and go undetected. The stress of transporting the plant from the greenhouse and replanting it may make a plant susceptible to exhibiting symptoms of black root rot and alert the gardener of a potential problem. If not, the contaminated plant and soil will be introduced into the garden or backyard greenhouse.


The spores of the fungus Thielaviopsis can live in the dust on plant pots, trays and flats used in the greenhouse. Any breeze can easily spread the spore-infected dust. Splashes caused by overhead watering systems can also spread the disease causing spores to spread throughout the greenhouse and lurk in the soil and on plants without showing any evidence. Potting mediums with a pH level higher that 5.5 to 6.0 offer a hospitable environment for black root rot disease to grow.


The best way to keep black root rot from attacking valuable greenhouse flowers is to protect the plants from stresses that make them vulnerable to the disease. Healthy flowers can resist the disease even when exposed to the fungus. Proper climate conditions and balanced nutrients will keep plants healthy and resistant to disease. Proper drainage is detrimental to fungi and beneficial to plants.


Because Thielaviopsis can survive in dust as well as in the soil, simple greenhouse housekeeping can help to control black root rot in the greenhouse. Keep the benches clean and sanitized to keep the dust down. Don’t let the dust build up on any supplies in the greenhouse, and refrain from reusing containers and trays that may harbor fungus spores.

Keywords: black root rot, greenhouse flower disease, greenhouse flower problems

About this Author

Patrice Campbell, a graduate of Skagit Valley College, has more than 20 years of writing experience including working as a news reporter and features writer for the Florence Mining News and the Wild Rivers Guide, contributing writer for Suite 101 and Helium, and promotional writing for various businesses and charities.