Nematodes are far more prevalent and a more serious problem than farmers think. What is more, they cannot be eradicated, but only managed, according to Prof Driekie Fourie of Integrated Pest Management at North-West University (NWU).
Fourie was speaking at the One Earth, Soil and Root Health Forum recently hosted by Syngenta.
She said an average of 12% of yield losses were attributed to nematodes in South Africa, while up to 60% were recorded in infested fields.
“I know of highly infested soya bean and dry bean fields where the crops were completely destroyed,” she added.
Root-knot nematodes (Meliodogyne spp) and lesion nematodes (Pratylenchus spp) were the biggest culprits.
“In high population densities, these nematodes typically cause discolouration of leaves and have a negative impact on root development. The problem can easily be mistaken for something else, so plant analysis is necessary to identify the cause,” Fourie said.
Research so far had identified sandy soils as the most vulnerable, but nematodes could also quickly multiply rapidly and cause major losses in clay soils. Contrary to popular belief, traditional maize-based rotational, such as maize, followed by sunflower, maize, and soya bean or dry beans, had been found to worsen the problem.
Research at NWU indicated that maize was a suitable host for the aggressive M. enterolobbi found for the first time in a grain production area on the Highveld.
A rotation programme therefore needed to include plant species or genotypes that would help break the life cycle of this species, Fourie said.
Knowledge of nematode and microbe complexes for row crops in South Africa was also very limited.
Grain SA, in partnership with nematologists and plant pathologists at NWU, the University of Pretoria and the Agricultural Research Council, was working towards a better understanding of these pests.
Stefan van Zyl, business manager for Syngenta Seedcare in SA, said there was no silver-bullet management solution. Management started with knowledge, which included ways to understand the severity, cause and scope of the problem.
Ongoing collaboration was also needed between growers, the crop protection industry, the seed industry, producer organisations, and researchers to better understand the problem and possible solutions.
Finally, on-farm action in the form of integrated pest management was required, van Zyl said.
This included seed treatments, in-furrow treatments, the use of nematode-resistant cultivars, protection against secondary infections, weed control and crops rotation.