Influence of nitrogen levels and plant spacing on the incidence of rice stem borers in Abakaliki, southeastern Nigeria
Field experiments were conducted under lowland conditions at the Africa Rice Centre (WARDA) Research Farm Abakaliki during 2006 and 2007 wet seasons to evaluate the effect of different nitrogen levels and plant spacing on the incidence of rice stem borers (Chilo zacconius Bles, Diopsis macropathalman Daman, Maliarpha separatalla Rog, Sesamia calamistis and Sciropophaga spp. Hamp.). Fields were laid out in split-plots, in randomized complete block design with three replications. Three nitrogen levels (0 kg N ha-1, 80 kg N ha-1 and 160 kg N ha-1) as the main- plot treatments were tried with three plant spacings (10 x 10 cm, 20 x 20 cm and 30 x 30 cm) as sub-plot treatments. The results from the two factors show that the incidences of stem borers were highest when rice treated with 160 kg ha-1 was planted at 10 x 10 cm plant spacing. Conversely, the incidence rates decreased significantly (p<0.05) as plots treated with lower dosage of nitrogen were planted at wider spacing. These results suggest that stem borer incidence could be controlled in Abakaliki by treating rice plots with 80 kg ha-1 of nitrogen and planting at 10 x 10 cm plant spacing, to increase plant population for optimum grain yields.
Keywords: Rice, nitrogen levels, plant spacing, stem borers, Nigeria