Onion stem nematode

Taxonomic position: Afrina wevelli is a nematode parasite classified within the order Tylenchida and the family Anguinidae. This microscopic worm acts as an endoparasite, invading the internal structures of host plants and causing systemic damage throughout the vegetation period.

Host crops: This pest primarily affects members of the Allium genus, including onions, garlic, and leeks. It is also found in various bulbous ornamental plants. Its ability to persist in the soil for several years makes it a formidable challenge for commercial vegetable production.

Biology and life cycle: The life cycle involves multiple larval stages that feed on plant cells. Under optimal conditions, the life cycle can be completed in a few weeks. Crucially, Afrina wevelli exhibits a high degree of adaptability, entering a survival state (anhydrobiosis) when conditions become dry, allowing it to survive extreme environmental stress.

Symptoms and damage: The damage is characterized by swelling, cracking of the basal plate of the bulb, and twisting of leaves. Infected plants show stunted development and are highly susceptible to secondary rot pathogens. This often leads to severe yield losses in the field and massive decay during post-harvest storage.

Protection measures: Management must be preventative to be effective:

• Source high-quality, nematode-free sets or seeds for planting.
• Implement strict crop rotation schedules avoiding susceptible crops for at least 4 years.
• Ensure thorough sanitation by removing crop debris that may harbor the pest.
• Use certified heat treatment for infested bulb sets before sowing.
• Monitor field boundaries to prevent the spread of the pathogen via irrigation water or machinery.