Onion neck rot

Onion neck rot is a destructive fungal disease caused by Botrytis allii. It primarily affects members of the Allium genus, including onions, garlic, and leeks. The pathogen is widespread globally and is considered one of the most critical post-harvest diseases, as it remains dormant during the early stages of growth and reveals its full impact only when bulbs are stored.

Symptoms typically manifest as tissue softening around the neck of the bulb, which appears water-soaked and sunken. As the infection progresses, a dense, grayish mold develops on the affected areas, consisting of fungal conidia. Over time, hard, black structures known as sclerotia emerge within the decaying tissue, serving as the primary survival mechanism for the fungus in the soil or crop debris.

The infection thrives under cool, damp conditions, particularly during the harvest season. If the onion tops do not dry out quickly or if they are harvested during rainy weather, the pathogen easily enters the bulb through the succulent, open neck tissues. Once stored, if the environment lacks proper ventilation and humidity control, the fungus spreads rapidly through bulbs in close proximity, leading to widespread decay.

The economic impact of neck rot is significant, as it can ruin entire harvests during storage. Infected onions lose their firmness, become mushy, and emit an unpleasant odor, rendering them completely unmarketable. Because the fungus can persist as sclerotia in the soil for years, it poses a recurring challenge for growers who do not rotate their crops or manage soil health effectively.

Integrated pest management strategies are essential for controlling Botrytis allii:

• Practice a crop rotation cycle of at least 3-4 years to reduce soil-borne inoculum.
• Harvest onions only during dry weather when the foliage has naturally collapsed.
• Ensure rapid and thorough curing of the bulbs in a well-ventilated area to seal the neck tissues.
• Store onions in cool, dry conditions with adequate airflow to maintain low relative humidity.
• Remove and destroy all infected plant debris to prevent carryover of sclerotia to the next season.