Sclerotinia bulb rot

Sclerotinia bulb rot is a destructive fungal disease caused by the pathogen Sclerotinia bulborum. This fungus primarily attacks the bulbs of various ornamental plants, leading to tissue decay, reduced plant vigor, and significant losses in both nursery and home garden production systems.

The disease frequently affects bulbous plants such as tulips, hyacinths, crocuses, and narcissi. The pathogen is highly persistent, capable of surviving for long periods in the soil as sclerotia, which are hard, black resting structures that act as the primary inoculum for future infection cycles.

Initial symptoms are often observed in early spring, characterized by premature yellowing and wilting of the foliage. Upon closer inspection of the bulbs, one can identify patches of soft, decaying tissue covered in white or greyish fungal mycelium. Over time, these patches develop the characteristic black sclerotia, which can be found either on the surface or embedded within the rotting bulb scales.

Environmental conditions play a critical role in the development and spread of Sclerotinia bulborum. Cool temperatures combined with high soil moisture and poor drainage create an ideal environment for the fungus to colonize roots and bulbs. Infection often spreads horizontally through the soil from plant to plant, as well as through the movement of contaminated bulbs.

Effective control strategies require a multi-faceted approach. Implementing a strict crop rotation schedule (avoiding susceptible species on infected plots for at least five years) is essential. Additionally, growers should use only high-quality, certified healthy bulbs, treat planting material with appropriate systemic fungicides, and ensure well-drained, slightly alkaline soil conditions to inhibit the pathogen's activity.