Influence of Nitrogen Fertilisation on Red Spider Mites (Oligonychus coffeae Nietner) and Overhead Volatile Organic Compounds in Tea (Camellia sinensis)

Abstract

Nitrogen fertilisation influences tea yields, quality and pests infestation levels. Red spider mites
reduce tea production in western Kenya during prolonged droughts. Nitrogen fertiliser use maybe
an agronomic practice that may influence infestation levels by mites. Overhead volatile compounds
(OVOCs) composition also influences infestations of tea by mites. Influence of nitrogenous
fertiliser rates on red spider mite infestations and OVOCS levels was determined. Mites
populations varied (pd less than 0.05) with nitrogenous fertiliser rates. High infestations were at 0 and
300 kg N/ha/year, and sharp decline between 150 and 225 kg N/ha/year. Green leaf volatiles
increased while some aromatic and terpenoid compounds decreased with increasing nitrogenous
fertiliser rates. Significant (pd less than 0.05) direct linear regressions between 1-penten-3-ol, 3-penten-
2-ol, E-2-hexenal, Z-3-hexenyl acetate and inverse relationship between 2-phenyl ethanol, ethyl
benzene, -methyl styrene, longifolene and ß-cedrene and nitrogenous fertiliser rates were
observed. Most aromatic and terpenoid compounds, which are repellents of mites, were highest
between 150 and 225 kg N/ha/year where infestations by mites were lowest. The recommended
fertiliser rates of 100 to 225 kg N/ha/year in Kenya also produce most repellents of mites,
protecting tea plants against infestations. Use of recommended nitrogen rates can protect tea
from infestations by mites.