Evaluation of stem bore control using parasitoids with different trap plants in maize(Zea mays L.)

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Mubanga, Chola Shadreck
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The University of Zambia
Maize in Zambia is a staple food crop. Its production, however, is threatened by pest damage which causes yield reduction and compromises the grain quality. Stem borers can cause 100% yield loss, however, Cotesia flavipes (Hymenoptera: Braconidae) and trap plants have been reported to reduce the damage. Establishment and impact of C. flavipes in Zambia‟s region II and other parts of region I are not known. A combination control method of C. flavipes as parasitoids and trap plants in Zambia is also not adequate. The study was conducted in two agro-ecological zones of Zambia, Lusitu (region I) and the University of Zambia field station (region II) during the 2015/ 2016 agriculture season. The specific objectives were: (1) to assess the parasitism of C. flavipes on stem borers in the traps and maize field of regions I and II; (2) to identify trap plants that can increase natural enemies and reduce stem borer attack in maize fields. Cow candy (Sorghum sudanense), Nutrifeed (Pennisetum spp.) and White Buffalo (Panicum maximum) varieties as trap plants were sown 3 weeks before planting maize (ZM 521 and MMV 409). The three trap plant varieties were sown around the maize, while a control had maize only and planted away from the other treatments. The following parameters were measured on both the open pollinated maize varieties and the trap plants; stem borer density, parasitism, leaf and cob damage, plant damage, maize yield and trap plant establishment. Data was collected at 18, 40 and 60 days after maize emergence. 5 and 10 plants were randomly sampled, destructive sampling method was used and stem borers were collected, reared and identified. The results obtained at UNZA indicated that stem borer attack varied at different treatments. Leaf damage by stem borers was significantly different at 18 DAE (v.r = 5.95; Fpr = 0.01; P<0.05) and 40 DAE (v.r. = 7.15; Fpr = 0.005; P<0.05). At 18 DAE Nutrifeed (mean=1.9a) trap plant was significantly different from the control (mean=2.8) and white buffalo (mean=3.03) but was not significantly different from Cow candy (Sudan grass; mean=2.23. Cow candy was not significantly different from control and White buffalo at 18 DAE, whereas at 40 DAE both Nutrifeed (mean=3.13) and Cow candy (mean=3.47) were significantly different from White buffalo (5.23) but not with the control (mean=4.5). In Lusitu leaf damage was significantly different among the trap plants only at 40 DAE (v.r = 4.9; 3df; Fpr = 0.019; P<0.05) and not at 18 and 60 DAE. UNZA results for borer tunnel length and number of stem borers both indicated significant differences among the trap plants at 40 DAE and not at 18 DAE and 60 DAE. Nutrifeed had the lowest mean number of borers and tunnel length, it was significantly different from White buffalo and control but not with Cow candy which was not significantly different from control and White buffalo. Cotesia flavipes was found to have established itself well in region II causing overall parasitism of 17.54% and 69.01% at 40 and 60 DAE. However, Parasitism was not significantly different across the growth stages and trap plants. Good cobs grain yield pointed to no significant differences among the trap plants, while stem borer damaged cobs showed significant differences among trap plants (v.r = 5.78; 3df; Fpr. = 0.011; P<0.05). Percentage damaged cobs showed significant differences among trap plants (v.r. = 3.81; Fpr. = 0.04; P<0.05); Nutrifeed induced the lowest cob damage and was significantly different from Cow candy but not significantly different from control and White buffalo. In conclusion, C. flavipes recoveries confirms its establishment in a non-release site of region II and the presence of Nutrifeed as a trap plant resulted in significant enhanced C. flavipes parasitism through attracting the larval parasitoids much more to the C. partellus. I therefore, recommend that small scale farmers must be encouraged to use Trap plants like Nutrifeed as part of the Conservation Agriculture Practice and that further research must be conducted identifying suitable leguminous companion crops that could be used in stem borer reduction and C. flavipes attraction.
Maize--Production--Zambia , Maize--Pest control