Foliar nematode

Foliar nematodes, caused by the Aphelenchoides genus, are microscopic parasites that pose a significant threat to a wide range of indoor and outdoor plants. Unlike soil-borne nematodes, these pests primarily inhabit the aerial parts of the host plant, specifically the leaves, where they move through water films to penetrate plant tissues through stomata.

These pests affect a diverse group of host plants, especially those grown in humid environments. Notable susceptible species include Gerbera jamesonii, various Passiflora L. cultivars, geraniums, and specific pelargoniums such as Pelargonium graveolens and Pelargonium peltatum. Primula species, including Primula malacoides and Primula obconica, are also highly susceptible to infection.

Symptoms typically present as distinct angular lesions that are limited by leaf veins. Initially, these patches appear yellow or light green, eventually turning dark brown or necrotic as the tissue dies. Heavy infestations lead to severe leaf distortion, chlorosis, stunting, and eventual defoliation, which severely compromises the aesthetic and physiological health of the plant.

The spread and development of foliar nematodes are highly dependent on moisture. Free water on the leaf surface is critical for their motility, allowing them to migrate from the lower leaves to the canopy. Greenhouse conditions characterized by high relative humidity, frequent overhead irrigation, and moderate temperatures provide an ideal environment for rapid population growth and disease transmission.

Management requires an integrated pest management approach. Key preventive measures include:

• Using pathogen-free stock plants.
• Avoiding overhead irrigation to keep foliage dry.
• Ensuring proper spacing to improve air circulation.
• Sanitizing tools and work surfaces regularly.
• Implementing systemic nematicides where permitted to manage established populations.