Flea beetle populations and economic yield of Okra as influenced by Nitrogen and 2, 3-Dihydro-2, 2-Dimethyl Benzofuran
AbstractNitrogen fertilisation and carbofuran applications impact plants, yet few studies examine their general impact on plant performance and plant susceptibility to insect pests and diseases when applied together. The performance of okra (Abelmoschus esculentus L. Moench) and infestations by flea beetles in relation to nitrogen and carbofuran applications were, therefore, evaluated under a humid tropical environment. Treatments comprised of combinations of four rates of 2, 3-dihydro-2, 2-dimethylbenzofuran or carbofuran (0.0, 0.5, 1.0 and 1.5 kg ha-1) and four levels of N- fertiliser (0, 40, 80 and 120 kg ha-1). The presence of Podagrica uniformis was recorded much earlier on the plants than Nisotra sjostedti. The population of either flea beetle remained lower throughout the vegetative than the reproductive phase. While N fertilisation resulted in higher insect count than where no N was added, carbofuran at 1.0 kg ha-1 and above significantly (P<0.05) depressed the flea beetle populations up to 5 weeks after planting. Differences in the carbofuran and N interaction had no statistical significance on insect count. All cases of applied
carbofuran and nitrogen increased earliness to maturity, plant height, total fruit number, fruit weight, fruit yield and net marginal returns. Higher doses of carbofuran in combination with nitrogen significantly increased earliness to plant maturity, fruit number per plant, fruit yield and net marginal returns. The best fruit yield was attained by combining 1.0 kg ha-1carbofuran with 80 kg N ha-1, while the best economic return was achieved by combining 0.5 kg ha-1carbofuran with 80 kg ha-1. Incidence of mosaic disease was suppressed with increasing doses of carbofuran
or decreasing doses of nitrogen.