Sterile is not always better for root disease management
As a plant pathologist, we preach that sanitation and keeping everything as clean as can be is the most important step in preventing diseases. Following good sanitation practices is crucial to reduce pathogen introductions into production facilities, especially root pathogens like Pythium, Phytophthora, Rhizoctonia, Fusarium, and Berkeleyomyces (formerly Thielaviopsis). However, when I was visiting with a deep-water hydroponic lettuce producer, I was reminded that developing a microbiome of beneficial organisms is an important factor in reducing disease development as well.
Beneficial microbes can inhibit plant pathogens through competition, antagonism, and induction of systemic resistance within the plant. While working with a grower having an outbreak of black root rot caused by Berkeleyomyces basicola on their lettuce crops within a deep-water pond system, we were trying to address the source of the pathogen and cleaning everything including draining the ponds, disinfecting them, and refilling with new water and nutrient solution. The problem persisted. Chemical fungicide control was not an option nor are any products labeled to control Berkeleyomyces in hydroponic culture. We also tried chlorination and hydrogen peroxide injection to kill spores and keep the water clean. Still, the problem persisted. Then, we tried incorporating beneficial microbes using commercially available products into the system and backing off the chemical injection a bit because some phytotoxicity was seen on the crop. And, it worked. Rafts, tools, and equipment are still cleaned and disinfected to reduce reintroducing the pathogen back into production; however, the ponds have developed a microbiome that is for now reducing disease development and producing a healthy crop. If you are not considered using a biofungicide, it may be something to add into your disease management program. Rosa Raudales and Cora McGehee wrote an excellent e-GRO Edible Alert on biofungicides for the control of root diseases that is worth reading (http://e-gro.org/pdf/E207.pdf).
Jean Williams-WoodwardAssociate Professor, University of Georgia
Jean is an Associate Professor and Extension Plant Pathologist at the University of Georgia. Jean provides statewide plant disease diagnosis and management recommendations for ornamental plants in greenhouses, nurseries, and landscapes. She also teaches three courses in plant disease diagnosis and ornamental pest management. She brings over 25 years of experience in working with ornamental plant producers and extension outreach providing education programs and on-site plant problem diagnostics.