Greenhouse Disease Management
Sclerotinia Disease
Sclerotinia disease, also called white mold, is most common outdoors but is observed occasionally in the greenhouse. Sclerotinia blight can cause root rot, stem rot, blighting of foliage and leaf petioles in a wide variety of greenhouse crops, including alyssum, begonia, gazania, geranium, gerbera, gloxinia, larkspur, lobelia, petunia, stocks, vinca, and zinnia.
Disease Cycle
Sclerotinia’s disease cycle typically starts from acrospores that are released from fungal bodies called apothecia (which are brown, cup-shaped fruiting bodies, 5 to 15 mm in diameter). Acrospores can travel for long distances and come in through greenhouse vents or doors. Sclerotinia needs high humidity and/or wet surfaces to thrive. It prefers cooler temperatures of 60 to 70 degrees F (15 to 21°C) but can develop at temperatures of 36 to 90 degrees F (2 to 32°C).
Symptoms
Depending on the crop or weed host, the Sclerotinia fungi can cause a blighting or rotting of any above-or below-ground part of the plant (See Figure 28.11). Initially, disease outbreaks are usually patchy and spasmodic. But if favorable temperature and moisture conditions prevail during the growing season, the incidence of the discase can be high and its development can be extensive.
Cultural Management Strategies
Sanitation is critical for managing Sclerotinia. Do not use unsterilized field soil in potting mixes. Avoid introducing untreated field soil to the greenhouse on tools or equipment, and keep weeds under control. For bench-grown crops, control can be difficult. Maintain dry foliage by minimizing overhead watering and dripping, and provide good air circulation through the crop canopy by ensuring good spacing.
Chemical Management Strategies
There are several effective fungicides for controlling Sclerotinia blight and crown rot, but these are preventative, not curative. Fungicide treatment is no substitute for sanitation. Rotate applications between chemical classes or FRAC codes to help prevent fungicide resistance from developing. Use contact fungicides in rotation with systemic fungicides. Appendix C, Fungicides and Bactericides Labeled for Greenhouse Use, lists fungicides and bactericides, labeled for control of plant diseases in greenhouses.
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