Warm, Wet Conditions + Full Plant Canopy: Perfect conditions for Sclerotinia
Late spring is the time when plants have grown into a fullcanopy covering the pot. When aprolonged period of cloudy and humid days occur, it is not unusual forSclerotinia to appear. Sclerotinia isalso called white mold because of the white, fluffy, mycelium growth. If humidenvironmental conditions continue, sclerotia (small, black irregular structures)develop within the mycelium growth. These structures can form on the decayedleaves, stems, and inside hollow stems.
Sclerotinia has a wide host range. At NCSU this spring, we had one pot ofcalibrachoa and a few cannabis plants become infected in separate greenhouses. I have also observed problems with hangingbaskets of petunias, scaevola, and lobelia, along with pots of gazania,gerbera, and poinsettias. Sclerotiniaalso infects many weed species.
The white fluffy mycelium and sclerotia aid in diagnosingthe disease. A sclerotinia problem canbe misdiagnosed as Botrytis (gray mold), so if in doubt, submit a sample to adiagnostic clinic for identification. Links to two excellent articles that contain additionaldisease details and control options are listed below.
Additional Resources and Control Options:
White mold (Sclerotinia sp.) showing up in greenhouses.Jae Byrne, Michigan State University
Control of Botrytis and Sclerotinia on ornamentals.
Ann Chase, Chase Consulting
Brian WhipkerProfessor, Horticulture, North Carolina State University
Brian E. Whipker is a professor of floriculture at North Carolina State University. He has an appointment split between extension and research, but also teaches the graduate level plant nutrition course at NC State. His specialization is plant nutrition, plant growth regulators, and problem diagnostics. He brings over 25 year of experience in diagnosing grower plant problems.