The effect of aqueous ginger (Zingiber officinale) extracts on the management of major pests of cabbage (Brassicae oleracea var.capitata)
Abstract
Insect pests are a serious constraint to cabbage production in Ghana. Every phenological stage in the life cycle of the crop has at least one major insect pest. Caterpillars of the diamond back moth (Plutella xylostella), the cabbage web-worm (Hellula undalis) and cabbage aphids (Brevicoryne brassicae) are the most serious pests of cabbage in Ghana. These pest cause percentage leaf damage between 18 % and 31 %. The attack of one or more of these pests may result in total crop loss. Their successful management is therefore critical to ensuring food security. The use of synthetic insecticides for the control of these pest has been the standard practice, however, an increasing awareness of the environmental hazards associated with insecticide use as well as the high costs of control has intensified the need for a less hazardous form of pest control. Biopesticides have long been an alternative to synthetic chemical insecticides for pest management because botanicals apparently pose little threat to the environment and to human health. The efficacy of aqueous extract of the rhizome of ginger, Zingiber officinale was therefore assessed for the control of the major insect pests of cabbage in the 2013 minor season and 2014 major season. Four concentration of the rhizome extract – 5 %, 10 %, 15 % and 20 % - were tested along with a synthetic insecticide (Abamectin) and control (water) to assess the potency of the extract. The synthetic insecticide, Abamectin was superior in reducing insect populations and compared favourably with the aqueous ginger extract for many of the parameters measured. For example, in the minor season, the mean pest numbers recorded for Brevicoryne brassicae was 0.15 for the abamectin and the least of 0.52 recorded in 15 % ginger-sprayed plots whiles in the major season, 0.20 mean numbers was recorded on abamectin sprayed plots and the least of 2.14 recorded on the 5% ginger-sprayed plots. The yields for plots of the aqueous ginger extract performed almost the same as the synthetic insecticide spray plots. Mean numbers of 0.57 kg was recorded for the insecticide spray plots and 0.72 kg, 0.45 kg, 0.50 kg, 0.53 kg for 5 %, 10 %, 15 % and 20 % ginger-sprayed plots respectively in the minor season. The insecticides - sprayed plots recorded the mean weight of 1.39 kg, whilst the least (0.77 kg) was recorded on the 20 % ginger sprayed plots in the major season. Even though the aqueous ginger extract could not completely manage the pest of cabbage, it reduced the numbers due to its repellant properties even though not as effective as the insecticide spray, Abamectin
Description
A thesis submitted to the Department of Theoretical and Applied Biology,
Kwame Nkrumah University of Science and Technology
in partial fulfillment of the requirements
Master of Science degree in Environmental Science.