White mold (Sclerotinia sp.) showing up in greenhouses

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Recently in the diagnostic lab we have seen several cases of disease caused by white mold. Infected plants included lobelia (stem rot) and gazania (blighting) and gerbera (crown rot). Sclerotinia has a wide host range including many annuals, perennials, vegetables and field crops. Disease symptoms include pre and post-emergent damping off, crown rot, and blighting of foliage and petioles. Small, hard, irregular, black structures called sclerotia may be present on or in plant tissue (especially inside stem and petiole tissue). White fluffy growth is produced on affected plant parts – this is most readily visible in high humidity.

Photo 1. Ganzania (blighting).

Botrytis and Lobelia.
Photos 2 and 3. Left, botrytis with Sclerotinia. Right, lobelia (stem rot).

Disease is spread mainly via sclerotia. These are long term survival structures, that are found in soil and on plant debris. Movement of these structures is the primary means of disease spread. Disease can also be spread by the movement of infected plant material. Under certain environmental conditions, mushroom like structures (apothecia) are produced and they release airborne spores.

Disease management is primarily based on avoidance of the pathogen. Field soil should be sterilized before using it in growing media. Susceptible crops should not be grown in areas with a history of white mold problems. Additionally, good sanitation is important to limit spread. Weeds should be controlled in production areas, because some weeds are hosts to Sclerotinia. Fungicide drenches can be used to protect plants from infection. Fungicides labeled for control of Sclerotinia in the greenhouse include chlorothalonil, thiophanate-methyl and PCNB.

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