How to fight White Mold (Sclerotinia) on Coleus


Coleus plants with white cottony-like growth, stem and leaf rot, and small, hard, black sclerotia were observed. This Alert describes and provides photos of symptoms observed on coleus caused by white mold (Sclerotinia sp.) also referred to as Sclerotinia stem rot or cottony soft rot. To diagnose white mold, submit plant samples to your preferred diagnostic lab.

An eight-week-old coleus (Solenostemon scutellarioides) crop was inspected because individual plants found sporadically across the greenhouse had started wilting, exhibiting watersoaked lesions and stem rot (Fig. 1). Upon closer inspection, plants were found to be infected with white mold (Sclerotinia sp.). White cottony-like fungal growth (Fig. 2) formed a mycelium that was observed growing across the substrate and plant surfaces (Fig. 3). Small clumps of mycelia were observed on the plant stem and leaf tissues (Fig. 4). Small, hard, black sclerotia (Fig. 5) were observed on the outside and inside (Fig.
6) of the diseased coleus stems.

According to crop records, initial symptoms were observed during week six of the coleus crop cycle. By week eight, significant plant growth amassed and air flow between plants was limited. Overhead watering maintained constant leaf wetness resulting in humid conditions within the plant canopy and the greenhouse temperature was 68 °F (20 °C). Unfortunately, week eight of the crop cycle coincided with an extended period of cool, low-light, rainy outdoor conditions which favored disease progression in the coleus crop.

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