Cottony leak

The disease is caused by the oomycete Globisporangium ultimum (formerly Pythium ultimum), a notorious soil-borne pathogen. It is highly aggressive and causes various types of rot, including damping-off of seedlings and the characteristic soft, watery decay of fruits known as cottony leak.

This pathogen has a wide host range affecting numerous crops, including vegetables and ornamentals. It is particularly devastating for cucurbits, such as watermelons, where the pathogen invades the fruit flesh directly through contact with moist soil during the ripening or storage stages.

The primary symptom is the rapid appearance of water-soaked lesions that quickly spread across the fruit. A dense, white, cotton-like mycelial growth forms on the surface of the lesions. Internally, the infected tissue breaks down into a watery, mushy mass, often emitting a foul odor.

The development of cottony leak is heavily influenced by environmental factors. High moisture levels, poor drainage, and moderate temperatures provide ideal conditions for the pathogen to thrive. The survival structures, known as oospores, allow the organism to persist in the soil for extended periods.

• Improve soil drainage to prevent surface water accumulation.
• Avoid harvesting fruits during or immediately after rainfall.
• Maintain strict sanitation practices in storage and packing facilities.
• Use crop rotation with non-host species to reduce soil inoculum.
• Apply appropriate fungicides as a preventive measure in high-risk areas.

Effective management requires a multi-faceted approach focusing on prevention rather than cure. Since Globisporangium ultimum is difficult to eradicate once it is established in the soil, preventing contact between the fruit and soil, and minimizing post-harvest humidity, are the most reliable methods for crop protection.