Evaluation of integrated pest management practices on nematode assemblages in a potato field in South Africa

Abstract

Mounting pressure to reduce the use of chemical pesticides globally necessitated this study to investigate the potential of a neem-amended organic manure product (Kalahari 3:1) to aid potato farmers in reducing plant-parasitic nematode (PPN) population densities and the subsequent damage they cause. The efficacy of an organic neem-amended manure product was compared to that of registered chemical nematicides in combination with grass cover cropping using White Buffalo grass (Urochloa mosambicensis (Hack.) Dandy.), representing a natural fallow period, in a field near Tzaneen, Limpopo province, during 2018-2021. The field was planted with the cultivar Sifra. Plant-parasitic and beneficial soil nematodes were extracted from roots and soil at four sampling intervals (pre-plant, 10 weeks after emergence, harvest and after fallow). Root-knot nematodes (RKN) were identified to species level, using morphological and SCAR-PCR techniques, indicating that Meloidogyne javanica and M. enterolobii were the predominant RKN species present in the trial site. The presence of M. enterolobii on potato in Tzaneen, Limpopo, is therefore, a new addition to the South African Plant Parasitic Nematode Survey (SAPPNS) database. Contrary to literature and expectations, Kalahari 3:1 (stand-alone or combined with chemical nematicides) was not able to reduce population densities of predominant PPN genera (viz. RKN, lesion, spiral and ring nematodes) in the soil or roots. The combination of Nemacur® 400 EC with Velum® Prime 400 SC provided the best control against PPN in roots and soil in this study. The use of Kalahari 3:1, a stand-alone treatment, did have a more positive effect on beneficial soil nematodes during the potato crop cycle than the standard nematicides. Increased beneficial nematode community composition and abundance, especially bacterivore abundance, were observed. Soil nematode communities were not related to soil physico-chemical properties in this trial. After a 27-month grass fallow period, the PPN abundance declined and bacterivore nematode abundance increased from pre-plant level. However, the fallow period and grass cover crop did not improve the overall soil health or soil nematode community and more interventions would be required to improve the health of this field.