Maize white rot

Maize white rot is a fungal disease caused by Sclerotinia sclerotiorum, a notorious pathogen with an exceptionally broad host range.

The fungus is classified within the family Sclerotiniaceae and is well-known for producing sclerotia—hardened, melanized survival structures.

These sclerotia allow the pathogen to persist in the soil for several years, even in the absence of susceptible host crops.

The mycelium of the pathogen is typically white and cottony, growing rapidly over plant tissues under suitable humidity conditions.

Identification is primarily based on the presence of these white fungal mats and the subsequent formation of irregular, black sclerotia inside or on the plant surface.

The fungus attacks the roots, stalks, and occasionally the ears of the corn plant, causing soft, watery rot to develop.

The disruption of the vascular system prevents water and nutrient translocation, leading to premature wilting and reduced grain fill.

Infected stalks lose structural integrity, becoming prone to lodging, which significantly complicates the mechanical harvesting process.

Severe infestations can lead to ear rot, where the cob is colonized by the fungus, reducing both the yield quantity and the seed quality.

Economic losses are compounded by the infection of the soil, which complicates future cropping choices in the affected field.

The disease cycle begins with the germination of sclerotia in the soil during periods of moisture and moderate temperatures.

Apothecia are formed, releasing millions of ascospores that are dispersed by air currents to infect healthy plants.

The most critical window for infection is during the reproductive stages of the corn, particularly when moisture remains trapped within the canopy.

Continuous wet weather combined with temperatures between 15°C and 25°C creates the perfect environment for rapid disease development.

As the growing season concludes, the fungus initiates the production of new sclerotia, which return to the soil to start the cycle again.

Initial symptoms are often masked as common wilting, but a closer look reveals characteristic white, fluffy fungal growth at the base of the stalk.

The internal tissue of the stalk degrades into a soft, mushy mass, often filled with dark, hardened fungal bodies.

Plants may show premature senescence and chlorosis, followed by the complete collapse of the stalk under stress.

If the infection reaches the ear, the husks may become bleached, and internal mold growth may cover the grain surface.

• Cottony white fungal mycelium
• Black sclerotia in stems
• Stalk softness and breakage
• Premature wilting of leaves
• Water-soaked stem lesions

Implementing a strict crop rotation program is essential; avoiding susceptible hosts like sunflowers or beans for several years is highly recommended.

Deep tillage can help bury sclerotia at depths where they are less likely to produce apothecia that can infect the current season's crop.

Managing soil drainage is critical, as excess moisture in the field promotes fungal activity and the spread of spores.

While no corn hybrids are fully immune, selecting cultivars with stronger stalks and better canopy architecture can reduce the risk of humidity entrapment.

Seed treatment and the use of targeted fungicides can provide a degree of protection, though cultural practices remain the primary method of management.