Exploiting The Insecticidal Potential of The Invasive Siam Weed, Chromolaena odorata L. (ASTERACEAE) in The Management OF Major Pests OF Cabbage And Their Natural Enemies For Enhanced Yield i

ABSTRACT

Cabbage is an important crop for many smallholder farmers in Africa and Asia, due to its nutritional and financial benefits. It is one of the popular vegetables consumed and cultivated by both urban and rural dwellers in Ghana. The production of cabbage in Ghana, however, is faced with numerous constraints especially insect pest infestations. Farmers have limited control options and therefore resort to the use of synthetic insecticides. Indiscriminate use of these insecticides has led to insect pest resistance problems, and also toxic residues in cabbage heads, posing high risk to humans, animals and the environment. Botanicals, which are derived from plant products are reported to be effective against many insect pests and are considered cheap, easily degradable and environmentally safe. Field experiments were carried out to determine the insecticidal potentials of siam weed, Chromolaena odorata L. at different rates (10, 20 and 30 g/L) in the management of the major pests of cabbage and its effect on their natural enemies during the major and minor seasons of 2014. The treatment consisted of three doses of C. odorata (10, 20 and 30g/L of water), 50 g/L of neem seed extract (as standard botanical), a conventional insecticide, Sunhalothrin® (with active ingredient Lambda cyhalothrin, EC) and tap water as a control. The treatments were laid out in randomized complete block design (RCBD) with three replications. The numbers of insect pests were recorded weekly on eight innermost cabbage plants per plot from transplanting until maturity. At maturity, cabbage heads obtained from each treated plots were counted and weighed and then classified as marketable or unmarketable depending on the level of damage. Costbenefit analyses of the different management options were also carried out. The diamondback moth (DBM), Plutella xylostella L. occurred only during the minor rainy season. The three rates of C. odorata had significantly lower number of aphid, Brevicoryne brassicae L. as compared to the Sunhalothrin. The 10 and 20g/ L of C. xv odorata sprayed plots recorded the highest build up of natural enemy populations as compared to 30g/ L of C. odorata and Sunhalothrin during the major rainy season. The cabbage plots sprayed with neem seed extract and siam weed extract (especially 10 and 20 g/L of water) had the highest yield, followed by the 30g/ L C. odorata and Sunhalothrin treated plots and the control The study also indicated that, the neem seed extract treated plots had the highest cost- benefit ratio followed by 20, 10 and 30g/L C. odorata treated plots, with the Sunhalothrin treated plots being the least. The findings from the current study, therefore, attest to the potential of 10 and 20g/ L of C. odorata as effective and economically feasible option for the management of insect pests of cabbage and other related vegetables, especially in smallholder farms and backyard gardens and other organic farming systems.