Relative Yield Loss of Potato in Fields Infested with Potato Cyst Nematodes and the Efficacy of Selected Control Products in Nyandarua County, Kenya

Abstract

Despite the rapid spread of potato cyst nematodes (PCN) in Kenya, data on associated yield loss is limited. The objective of this study was to determine the efficacy of four nematicides and relative yield loss associated with PCN damage. Three on-farm sites with varying PCN densities (low; 1-9, moderate; 10-39, and high; 40-80 cysts in 100 g/soil) were selected for the study in Nyandarua County during the 2021 long and short rains seasons. Treatments consisted of three potato cultivars namely Desiree and Shangi (susceptible) and Manitou, which is partially resistant. The four PCN control products tested were, fluopyram, oxamyl, azandirachtin (commercial neem extract) and Paecilomyces lilacinus. The experiments were set up in a randomized complete block design, in a split plot arrangement, with varieties as the main plots, and PCN control products including the control as the sub-plots. Treatments were replicated three times. The reproductive index of the nematodes ranged from 0.17 to 2.39 during the long rains and from 0 to 4.13 during the short rains season. Relative yield loss attributed to PCN infection varied from 6.3% to 80.5% during the long rain season and from 5.5% to 73.3% during the short rain season. The magnitude of yield losses was dependent on susceptibility of the variety and the initial PCN population density. This study has demonstrated that PCN are already causing substantial yield losses especially in heavily and moderately infested fields. The study demonstrated that oxamyl was the most effective nematicide in reducing PCN numbers and yield losses. Farmers are advised to take appropriate measures to prevent spread and buildup of the nematodes.