White mold in corn, caused by the soil-borne fungus Sclerotinia sclerotiorum, remains one of the most destructive diseases affecting commercial production in the upper Midwest and other humid regions. The pathogen thrives in cool, moist conditions, often flourishing in dense canopies where airflow is restricted, leading to significant yield loss and grain quality reduction. Unlike many foliar diseases that primarily affect leaves, white mold directly attacks the ear, husk, and stalk, compromising the entire structural integrity of the plant.
Understanding the White Mold Pathogen
The disease cycle begins with sclerotia, hardy survival structures that lie dormant in the soil for years until favorable conditions trigger germination. These sclerotia can produce apothecia, small cup-shaped structures that release spores into the air during specific humidity and temperature windows. Corn becomes vulnerable primarily through silk infection, which occurs when spores land on the silks and grow down into the ear, or through direct colonization of the husk and ear tip during the late vegetative stages.
Identifying the Disease in the Field
Visual Symptoms on Different Plant Parts
Early detection is critical for management, and symptoms vary by plant part. On the ear, a white, fluffy mycelial growth develops rapidly, often completely covering the kernels with a distinctive woolly appearance. Husks may appear water-soaked and tan, while infected kernels shrink and become discolored. Stalk symptoms are particularly insidious, as the fungus can girdle the node, leading to sudden lodging (stalk breakage) long after the ear has been harvested.
Differentiating from Other Corn Diseases
Misdiagnosis is common, as other pathogens like gibberella or fusarium can cause ear rot. However, white mold is distinguished by its characteristic white, cottony growth rather than the pink or reddish spore masses associated with gibberella. Furthermore, while many ear rots produce a foul odor, white mold typically emits a more earthy, musty smell. Careful examination of the husk tissue, looking for the specific white mycelium adhering to the surface, is the most reliable field diagnostic method.
Factors Influencing Disease Severity
Environmental conditions play a pivotal role in the severity of an outbreak. Cool temperatures between 60°F and 80°F, coupled with high humidity or frequent rainfall during silking, create the ideal environment for infection. Dense planting populations and excessive nitrogen fertility can exacerbate the issue by promoting a thick, closed canopy that retains moisture for extended periods. No-till or reduced-till farming systems that leave sclerotia on the surface also contribute to higher inoculum levels in the soil. Integrated Pest Management Strategies Cultural and Agronomic Practices Managing white mold relies heavily on an integrated approach that combines cultural practices with resistant genetics. Selecting hybrids with documented white mold tolerance is the first line of defense. Implementing strategies that improve airflow, such as wider row spacing or strategic plant population adjustments, can significantly reduce canopy humidity. Rotating to non-host crops like soybeans or small grains for multiple seasons helps reduce the soil-borne sclerotia population, breaking the cycle of infection.
Integrated Pest Management Strategies
Cultural and Agronomic Practices
Chemical Control Options
While cultural practices are foundational, fungicide applications can provide critical protection during high-risk periods. Timing is everything; the most effective window for application is typically during the late vegetative stages (VT-R1), coinciding with silking and pollen shed. Growers must choose products labeled for white mold control in corn and follow label instructions precisely to ensure proper coverage and efficacy. Resistance management is vital, so rotating fungicide modes of action is recommended to prevent the development of resistant pathogen populations.
