One of our local greenhouse growers struggled with Pythium infections in pansy earlier this year. Now, poinsettia are infected with the same root rotting/damping off fungus.
So, why would Pythium be a recurring problem? Simple. Sanitation.
Sanitation is critical for greenhouse production, landscapes, orchards, and gardens. In this greenhouse, fungal propagules are obviously spreading via debris, hoses, shoes, tools, drainage water, and more. Also, Pythium favors soilless mixes, where there's no competition. Growers should verify that potting mix is not contaminated and that containers are sterilized before reuse.
Moreover, greenhouses must be disinfested between crops, so that disease-causing propagules are not carried over from one crop to another.
Once a greenhouse is infested with Pythium, fungicides are required for disease management. A single fungicide application will not be sufficient to manage disease, so a regular schedule should be employed. Rotate fungicides by FRAC group (mode of action), avoiding two consecutive applications of any particular group and observing maximum numbers of applications per season. Fungicides effective against Pythium include:
· mefenoxam (Subdue MAXX) FRAC 4
· etridiazole (Truban/Terrazole) FRAC 14
· propamocarb (Banol) FRAC 28
· dimethomorph (Stature) FRAC 40
· phosphorus acids (Aliette, Alude, Vital) FRAC 33
· etridiazole + thiophanate methyl (Banrot) FRAC 14 + 1
For more information on disease management of poinsettia or other greenhouse crops:
Greenhouse Sanitation http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdfFungicides for Management of Diseases in Commercial Greenhouse Ornamentals http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdf
Poinsettia Diseases http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-2.pdf