Peanut stem nematode

The peanut stem nematode (Ditylenchus arachis) belongs to the phylum Nematoda, class Chromadorea, order Rhabditida, and family Anguinidae. This is a microscopic worm that has adapted to an endoparasitic lifestyle within plant tissues.

This pest is a highly specialized plant-parasitic nematode. Unlike many related species, it thrives inside stems, fruits, and underground parts of the plant, migrating actively through soil moisture and intercellular spaces of the host.

Visually identifying this nematode without laboratory equipment is impossible due to its tiny size (less than 1 mm). Phytosanitary analysis of plant tissue and soil samples is required for accurate identification.

The life cycle consists of an egg, four larval stages, and an adult. The nematode can remain viable in dried plant residues for a long time by entering an anabiotic state under unfavorable conditions.

Population dynamics are directly dependent on soil moisture and ambient temperature. Optimal conditions for rapid reproduction include warm weather and high humidity, which facilitate the migration of larvae to new plant tissues.

The primary host plant is the peanut (groundnut). The pest damages underground plant parts, including the hypocotyl, roots, and especially the fruits (pods) and seeds, leading to yield loss.

Besides peanuts, this nematode can infect a wide range of weed species in the field, which allows the pest to survive and persist even in the absence of the main crop.

Nematodes penetrate plant tissues and feed on cell contents, causing cell wall degradation and disrupting the vital physiological processes in the affected plant organs.

Severe infestations result in significant harvest loss. Affected pods are often deformed, with darkened and brittle shells, making the produce unsuitable for commercial sale.

Indirect damage occurs because the wounds created by the nematode act as entry points for secondary bacterial and fungal infections, which further exacerbate rot and decay.

The first sign of infestation is general plant stunting. Peanut plants lag in development, leaves may yellow, and stems may appear thinner than healthy ones.

Characteristic dark spots or ulcers form on underground stem parts. Tissues develop a cork-like structure, becoming loose and necrotic due to the nematode activity.

When pods are opened, one may find hollow spaces or a dark powdery mass where seeds should be. In cases of severe infestation, peanut seeds become shriveled and blackened.

Roots often show excessive branching or necrosis of fine rootlets, which severely limits the plant's ability to take up water and essential nutrients from the soil.

• Wilting of plants during the day.
• Presence of brown lesions on the surface of pod shells.
• Reduced germination rates when using infected planting material.

The primary control method is the use of healthy, certified planting material that is free from plant-parasitic nematodes. Seeds must undergo mandatory phytosanitary inspection.

Strict adherence to crop rotation is a critical defense mechanism. Including antagonistic crops or non-host plants in the rotation cycle helps reduce the nematode population density in the soil.

Rigorous weed management in peanut fields denies the nematode alternative food sources and reservoirs, which significantly slows down its reproduction during the growing season.

After harvest, deep plowing and the destruction of crop residues are essential. Clearing the field of debris removes the environment in which the pest survives the off-season.

Chemical nematicides are only justified in areas with extreme infestation. However, priority should be given to agronomic practices, as soil fumigation is expensive and requires specialized equipment for proper application.