Responses of the citrus nematode population densities post-application of Nemarioc-AL phytonematicide and aldicarb synthetic nematicide

Abstract

Density-dependent growth patterns suggested that under phytonematicides population densities of plant-parasitic nematodes could either be stimulated, neutral or inhibited, thereby resulting in ‘inconsistent results' concept. The objective of this study was to determine whether post-application sampling of the citrus nematode (Tylenchulus semipenetrans Cobb) population densities under untreated control, Nemarioc-AG phytonematicide and aldicarb on rough lemon (Citrus jambhiri Lush. ) seedlings could provide quantitative evidence of ‘inconsistent results'. Uniform three-month old C. jambhiri seedlings in plastic pots containing 2700 ml growing mixture were each inoculated with 10000 T. semipenetrans eggs and second-stage juveniles (J2). A week after inoculation, seedlings were split into three groups of seventy each and subjected to once-off treatment of untreated control, 2 g Nemarioc-AG phytonematicide and 2 g aldicarb. Five seedlings from each group were randomly placed on greenhouse benches to serve as a sampling block, with a total of 14 blocks. The entire block was sampled on a weekly basis and assessed for final nematode population density (Pf). After the final assessment, Pf under untreated control over increasing sampling intervals exhibited positive quadratic relations, with the model explaining 90% associations, with optimum Pf of 13804 eggs and J2 at six weeks post-application. In contrast, Pf over increasing sampling intervals under phytonematicide and aldicarb exhibited negative quadratic relations, with the model explaining 95 and 92% associations, respectively. The two had minimum Pf at 974 eggs and J2 and 2205 eggs and J2, respectively, each at approximately six weeks. In conclusion, opposite temporal cyclic nematode population growth patterns post-application of nematicidal products and untreated control provided empirically-based evidence of ‘inconsistent results' in nematode management under phytonematicides.