White mold of stem

The causative agent of white mold is the fungus Sclerotinia sclerotiorum. This destructive pathogen is known for its ability to attack a wide range of host plants, leading to tissue decay and plant collapse. The fungus survives in the soil through the production of sclerotia — dark, hardened survival structures that can persist in the ground for several years, ensuring the pathogen remains a threat to future crops.

White mold has an extremely broad host range, affecting over 400 species of plants. In agricultural settings, it is a devastating disease for sunflowers, canola, soybeans, and various leguminous vegetables. Because the fungus can infect both the roots and the stems, it poses a constant risk to high-value broadleaf crops in many regions of the world.

Initial symptoms include soft, watery lesions on the stem that rapidly expand. Under conditions of high humidity, these lesions become covered with a fluffy, white mycelial growth, which gives the disease its common name. As the infection progresses, the internal pith of the stem is destroyed, and the pathogen forms characteristic hard, black sclerotia inside or on the surface of the plant tissue.

Environmental factors play a decisive role in the development of the disease. Prolonged periods of cool, wet weather, along with high humidity levels, are ideal for fungal growth and spore production. Dense plant canopies that limit air movement create a microclimate favorable for the rapid spread of the pathogen, often resulting in severe localized outbreaks within a field.

The impact of white mold on yield can be catastrophic. By disrupting the vascular system, the fungus prevents the flow of water and nutrients, causing rapid wilting and plant death. Yield losses can be substantial, and the presence of sclerotia in harvested grain significantly reduces the market value and storability of the product, often requiring expensive cleaning processes.

Management strategies focus on reducing the pathogen population in the field:

• Rotating non-host crops like corn or cereals to break the infection cycle.
• Using certified, pathogen-free seeds to prevent field contamination.
• Managing field moisture by optimizing plant spacing and row orientation.
• Deep plowing to bury sclerotia at depths that inhibit their germination.
• Applying targeted fungicides during the flowering stage, which is the most vulnerable period.