Controlling nematodes in grain crops

The grain production season is approaching and soil-dwelling nematodes are re-emerging after winter. Farmers should start monitoring these pests now, say Prof Driekie Fourie and Dr Gerhard du Preez at North-West University’s Unit for Environmental Sciences and Management.

Root-knot and lesion nematodes (Meloidogyne and Pratylenchus spp respectively) are the most important nematodes faced by grain farmers in South Africa. Increases in soil temperature and the presence of moisture lead to a resumption of activity after winter dormancy. This is especially the case at present, following the abundant rain in most local crop production areas in summer.

In their infective stages, these microscopic organisms use their reserve energy to move through the soil by means of the water layers surrounding soil particles in search for the roots of possible hosts. They infect and feed on the roots of grains and weeds, and can cause serious crop damage.

Weeds should therefore be removed from grain lands to prevent infestation, as nematodes can survive in their roots. Live root-knot nematode females have been found in the middle of winter in the Free State on ragwort bushes. These abundant, yellow-flowered weeds create the ideal habitat for the nematodes, which start reproducing as soon as the soil temperature rises.

RAPID REPRODUCTION

Two of the most prevalent rootknot nematodes in South Africa, M. incognita and M. javanica, can develop at fairly low base temperatures of 9,8°C and 10,6°C respectively.

A single female root-knot nematode can produce up to 1 800 eggs (reported in a susceptible soya bean cultivar) within 20 to 30 days of infecting the root of a host plant at a soil temperature of 26°C. This means that a single female, which can live for an average of three months, has the potential to produce approximately 5 400 eggs in one season.

Should the soil temperature increase, however, the nematode could reproduce within a shorter time, which is why farmers should keep their grain lands free of weeds.