Effect of Different Levels of Nitrogen in Liquid Fertilizer on the Population Dynamics and within Plant Distribution of Aphis gossypii and Thrips palmi and Yield of Eggplant

A study was conducted in 2011 at the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana to evaluate the effect of different levels of nitrogen in liquid fertilizer on the population dynamics and within plant distribution of Aphis gossypii (Glover) and Thrips palmi Karny on eggplant (Solanum melongena L). In the major cropping season, whereas significantly more A. gossypii aggregated on the leaves in the lower canopy than the upper canopy in the treatment 2 (Sidalco liquid fertilizer + 1% sulphate of ammonia solution), treatment 3 (Sidalco liquid fertilizer + 0.5% sulphate of ammonia solution) and treatment 4 (Sidalco liquid fertilizer), no significant differences were recorded in the densities of the insect on the leaves in the canopy levels in the control (treatment 1). In the minor cropping season, it was only in the treatment 4 that significantly more A. gossypii aggregated on the leaves of the lower than the upper canopy. T. palmi densities were higher in the minor than in the major cropping season. In the major cropping season, it was only in the control that significantly more T. palmi aggregated on the leaves of the lower than the upper canopy. In the minor cropping season, however, significantly more T. palmi aggregated on the leaves of the lower than the upper canopy of plants on treatment 3 plots. Plots with the highest doses of N received the highest number of A. gossypii and T. palmi in both cropping seasons. The plots with the highest doses of N recorded the highest yield in both seasons. The study showed that higher levels of N in the liquid fertilizer increased aggregations of A. gossypii and T. palmi, and increased levels of N also resulted in increased yield.