EVALUATION OF SIX PEST MANAGEMENT STRATEGIES ON KEY INSECT PESTS OF TWO CABBAGE VARIETIES (Brassica oleracea var. capitata L.) IN THE KETU SOUTH MUNICIPALITY OF THE VOLTA REGION OF GHANA.

ABSTRACT Cabbage is a well-known vegetable grown in Ghana due to its nutritional value and serves as a source of livelihood for small scale farmers. Its cultivation is constraint by insect pests such as Plutella xylostella (L) (Lepidoptera: Plutellidae), Hellula undalis (Lepidoptera: Crambidae) and Brevicoryne brassicae (Aphididae) which cause significant damage and yield loss. Farmers especially those in the Ketu South municipality of the Volta region apply synthetic insecticides 12-15 times in one season to produce damage free cabbage heads and this method of control has been proven to be detrimental to consumers, natural enemies and the environment. It is against this background that an effective and environmentally friendly approach considering biopesticide, botanical and shallot as a repellent crop was explored in this study. Two cabbage varieties, Oxylus and KK cross were subjected to six pest management strategies; aqueous neem seed extract (75kg/ha at 50g/l of water), Bypel 1® (PrGV+Bt) (2kg/ha at 1.5g/l of water), shallots planted 14 days prior to cabbage transplanting, shallot planted 7 days prior to cabbage transplanting and shallot planted with cabbage on the same day combined with a short duration of neem spray and untreated control for two seasons in 2016/2017. The experiment was set up in a completely randomized design with a split-plot treatment arrangement with three replications. Main plots were the cabbage varieties whilst the sub plots were the six pest management strategies. The two biopesticides were applied after the first sampling of insects and thereafter every week. The results showed that plots treated with Bypel 1® had the least number of P. xylostella, and H. undalis but did not differ significantly (F5, 22 = 6.17, P = 0.0010 and F5, 22= 45.98, P = < 0.0010 P. xylostella both seasons; F5, 22 = 4.77, P = 0.0040 and F5, 22 = 9.05, P < 0.0010 H. undalis both seasons) from the other treatments, except for the control which had the highest population. Shallot planted the same time with cabbage sprayed with a short duration of neem had the lowest aphid score (0 and 1) with the highest on control plots (4 and 5). Other insect pests observed in the field were Bemisia tabaci, Thrips tabaci, Trichoplusia ni, Zonocerus variegatus and Empoasca spp. Fewer numbers of T. tabaci, T. ni, Z. variegatus were recorded on Bypel 1® and aqueous neem seed extract treated plots, but no significant differences were observed with other pest management strategies except in the control plots. B. tabaci numbers were least in Bypel 1® and Neem plots and highest in control plots. Apart from P. xylostella and H. undalis whose populations were highest on KK cross, the oxylus variety had higher populations of all the other pests but differences were not significant, except for B. tabaci with a significantly higher population on oxylus. The interactions between varieties and various strategies on P. xylostella, H. undallis and B. brassicae numbers for both seasons were not significant (F5, 22 = 0.18, P = 0.9690 and F5, 22 = 0.44, P = 0.8180 for P. xylostella; F5, 22 = 0.55, P = 0.7380 and F5, 22 = 0.61, P = 0.6960 for H. undalis and F5, 22 = 0.22, P = 0.9480 and F5, 22 = 0.34, P = 0.8840 for B. brassicae, respectively), indicating that the two varieties responded to the six pest management strategies in a similar manner. Shallot plots planted 14 days before transplanting cabbage had the highest numbers of the natural enemies (hoverflies, ladybirds and spiders) while C. plutellae was highest on shallot planted 7 days prior to cabbage transplanting and control plots. The yield and marketability of cabbages from the various pest management treatments were ranked in the following order of decreasing magnitude: Bypel 1® > sole neem > shallot with short duration Neem > shallot planted 14 days prior cabbage > shallot planted 7 days prior cabbage > control. Oxylus produced medium size heads which were more marketable and stored longer than KK cross with larger heads and greater head rots. This study demonstrated the potential of biopesticides and shallot as a repellent crop in the management of insect pests of cabbage. This could contribute to boosting the vegetable (cabbage) growing industry and positively impact on vegetable farmers‘ livelihood in the Volta region and the physical health of consumers.