Effects of N-fertilization and spacing on african rice gall midge <i> Orseolia oryzivora </i> harris and gagn&eacute i a sub-humid area of southeastern Nigeria

Abstract

Nitrogen fertilization and spacing hold a strong promise in the integrated management of rice insect pest problem. Therefore, three levels of urea: 0, 80 and 160 kg N ha -1 and three spacings: 10-cm x 10-cm, 20-cm x 20-cm and 30-cm x 30-cm were evaluated for two years in Abakaliki, Nigeria, for the control of rice gall midge. The experiment was set up using split-plot arrangement in a randomized complete block design (RCBD) with three replications. Results of the trial showed that nitrogen significantly increased incidence by gall midge (P<0.05) with 160 kg N ha -1 recording the highest incidence of 50.95% and 36.01% in 2002 and 2003 trials, respectively. Similarly, incremental doses of urea n-fertilizer increased the grain yield of rice but only up to 80 kg N ha -1 . Beyond this level further n-fertilization had no effect. Generally, increasing plant population significantly increased the incidence by the midge (r = 0.93 and 0.99 in both years). Conversely, grain yield was significantly reduced with increasing population. Differences among treatment combinations between nitrogen and spacing however did not produce any significant effect.