MISSISSIPPI STATE – Researchers at Mississippi State University have found a cost-effective and environmentally friendly strategy for fighting one of the most serious soil-borne diseases in poinsettia production.

Pythium stem and root rot is a common problem in poinsettia production because the fungus thrives in cool, saturated and poorly drained soils, said Maria Tomaso-Peterson, associate research professor in MSU’s Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology.

MSU researchers found a way to use organic methods and fewer fungicides to successfully fight this pathogen.

“Pythium is a widespread fungus. Plants are cross-contaminated by splashing water or soil from pot to pot,” Tomaso-Peterson, also a researcher for the Mississippi Agriculture, Forestry and Experiment Station, said. “In nursery management, producers treat the plants when they transplant cuttings to the pot. Once the disease is established, it’s too late to treat, so growers have to use a fungicide early in the season to make sure they have a healthy crop.”

The standard conventional fungicide is effective but expensive, and there is a high risk that the fungus will become resistant to the chemical.

“Managing resistance to important fungicides is a key component of a disease management program,” she said. “One of the strategies we have researched is integrating biofungicides.”

Tomaso-Peterson said biological agents are not conventional fungicides or chemicals, but organic methods of fighting fungi or other harmful microorganisms.

Tomaso-Peterson and Mengmeng Gu, assistant Extension professor in MSU’s Plant and Soil Sciences Department, tested the effects of using a biocontrol agent alone and in conjunction with conventional fungicides.

“We found that a reduced rate of the conventional fungicide, when used with a biological agent, resulted in plants that didn’t rot and had similar growth to the label rate of conventional fungicides,” Tomaso-Peterson said. “This is beneficial to growers because it reduces their impact on the environment. It also reduces the risk of the pathogens adapting to the fungicides and becoming resistant and may save producers money by reducing the amount of fungicide they use.”

Gu said Mississippi greenhouse operations grow poinsettias from late summer through fall and early winter. Pythium root rot can develop at any stage of poinsettia production, so early intervention is a key strategy.

This research benefits an estimated 20 wholesale poinsettia producers in the state who grow an estimated 200,000 pots of poinsettias at a wholesale value of nearly $1 million, said Gu.

“Reducing the use of conventional fungicides through disease-tolerant plants and the use of biofungicides will reduce the potential impact on everyone associated with the process, from production to retailing to the consumer because they will be exposed to fewer chemicals,” Gu said. “This project will also help reduce the environmental impact caused by using a conventional fungicide.”