Economic performance of the ‘push–pull’ technology for stemborer and Striga control in smallholder farming systems in western Kenya

The ‘push–pull’ technology (PPT), developed in Africa, offers effective control of cereal stemborers and Striga weed in maize-based cropping systems. It involves intercropping maize with desmodium, Desmodium uncinatum, with Napier grass, Pennisetum purpureum, planted as border around this intercrop. Desmodium repels the stemborer moths (push) that are subsequently attracted to the Napier grass (pull). Desmodium also suppresses and eliminates Striga. We assessed economic performance of this technology compared to the conventional maize mono- and maize–bean intercropping systems in six districts in western Kenya over 4–7 years. Ten farmers were randomly recruited in each district and each planted three plots representing the three cropping systems. The cost–benefit analyses were carried out, together with the systems’ net returns to land and labour and their discounted net present values (NPV). Maize grain yields and associated gross margins from the PPT system were significantly higher than those in the other two systems. Although the production costs were significantly higher in the PPT than in the two cropping systems in the first cropping year, these reduced to either the same level or significantly lower than in the maize–bean intercrop from the second year onwards in most of the districts. Similarly, the net returns to land and labour with the PPT were significantly higher than with the other two systems. The PPT consistently produced positive NPV when the incremental flows of its benefits compared to those of the two conventional systems were discounted at 10–30%, indicating that PPT is more profitable than the other two systems under realistic production assumptions. PPT is thus a viable option for enhancing productivity and diversification for smallholder farmers who largely depend on limited land resource. Hence, enhancing farmers’ access to less costly planting materials and promoting quality education and training in the use of this knowledge-intensive technology could stimulate its successful adoption.     

Non-target effects of the ‘push–pull’ habitat management strategy: Parasitoid activity and soil fauna abundance

We assessed the non-target effects of a habitat management system (‘push–pull’) on maize stemborer specialist natural enemy activity and soil Collembola. Two study sites in western Kenya were sampled. There were two treatments at each site, maize monocrop and ‘push–pull’. The latter comprised an intercrop of maize and Desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as a trap crop planted around the edge of the plot (spaced 1 m from main crop). Trichogramma spp. were recovered from stemborer eggs while Cotesia sesamiae and Cotesia flavipes were recovered from stemborer larvae, and Dentichasmias busseolae from pupae. Mean number of eggs parasitized was significantly higher in the maize monocrop than in the ‘push–pull’ plots however proportions parasitized did not differ between the two systems. The number of larvae and pupae parasitized and dead from causes other than parasitism similarly did not differ between cropping systems. Proportions of larvae and pupae parasitized were significantly higher in the ‘push–pull’ than in the monocrop plots, indicating that the activity of larval and pupal parasitoids was enhanced. C. sesamiae female wasps were attracted to the volatiles from Desmodium flowers but not those from the leaves in a four-arm olfactometer bioassay. A total of 1530 individual Collembola in seven families were recovered from the plots. The ‘push-pull’ strategy did not have any significant effect on Collembola abundance and dominance. The factors underlying these observations and their implications are discussed.     

Influence of common carp on apple snail in a rice field evaluated by a predator - prey logistic model

The hypothesis that common carp can be used for the control of apple snails in rice fields was tested experimentally. In a rice field, 12 plots of 4 2 5 m were set and enclosed by plastic walls to prevent snail emigration and immigration. The experiment continued from June to September. Three replicated treatments were used for the plots: zero, four and 12 carp were released, giving carp densities of 0.0, 0.2 and 0.6 m^?2, respectively. Snail densities were estimated by the Jolly-Seber mark-recapture method. Newly laid egg masses were counted and measured for size, and hatching was monitored. The numbers of eggs per egg mass (y) were estimated using a regression equation obtained from the product of the maximum length and width of the egg mass (x): y =0.10x^1.24. Using these measures and the monthly mean hatching rate obtained from eggs laid in two outdoor aquaria from April to September, the number of hatched eggs was used to estimate the birth rate over a given time. A logistic model incorporating these estimates revealed that the snail population proliferated only in the zero-carp plot throughout the experiment. The study, together with other reports on snail longevity, predicts that a snail population would be eliminated in 2 years at a stocking density of 2000 carp hectare^?1, if no immigration of the snail occurred.