Impact of Insect Infestation on Plant Damage and Yield of Roselle [Hibiscus sabdariffa L.] in Benue State, Nigeria

Impact of insect infestation on growth and yield of Roselle (Hibiscus sabdariffa L.) was evaluated at the Teaching and Research Farm of University of Agriculture, Makurdi, in the 2016 cropping season. An early and late crop (as main plot), of the red (H. sabdariffa sabdariffa) and green (H. sabdariffa altissima) types (as subplot) were planted in Randomized Complete Block Design (RCBD) with split-split-plot arrangement. Four weekly application of 100 g a.i/ha of cypermethrin + 400 g a. i./ha of dimethoate constituted sub-subplot treatments. All treatments were replicated three times. Insects were visually counted in 1 m2 area in two rows of each plot. The dominant insect pests included Monolepta thomsoni, Nisotra sjostedti, Dysdercus volkeri and Oxycarenus hyalinipennis. The early crop differed significantly (having 9 % wider stem girth, 2x more branches/stem, and 1.5x more leaf damage) from the late crop. The green Roselle had more pod (2.5x) and seed (1.1x) damage and gave from 1.3 – 1.5x lower calyx, pod and seed yield. Plant growth and productivity were significantly higher in sprayed than in the unsprayed plots. Plants sprayed at both vegetative and reproductive stages were the most productive having significantly more fresh leaf biomass (2.5-103.6x), calyx yield (2.6-2.8x), pod yield (2.2-7.4x), seed yield (3.1-11.0x) sequel to more vigorous growth and less pod damage (2.0-44.6x) and seed damage (1.8-8.6x). Cost-benefit analysis indicated that the red Roselle was more profitable than the green, the late crop was more profitable than the early, and protection at both vegetative and reproductive stages was more profitable than other spray regimes returning N440,291.25/ha, N755,291.5/ha, and N397,236.0/ha for leaf, calyx and seed valuation, respectively. Insecticidal protection of the crop has been shown to mitigate drop damage and return profit.