Stemborers and Striga are the major pests of cereal crops in Eastern and Southern Africa. Spraying with pesticides is not only expensive and harmful to the environment, but usually ineffective as the chemicals cannot reach deep inside the plant stems where stemborer larvae reside.
|Stemborers and Striga|
The Chemical Ecology Group at Rothamsted in partnership with the International Centre of Insect Physiology and Ecology (ICIPE) have developed a habitat management strategy which manipulates the agro-ecohabitat. The approach relies on a carefully selected combination of companion crops planted around and among maize or sorghum plants. Both domestic and wild grasses can help to protect the crops by attracting and trapping the stemborers. The grasses are planted in the border around the maize and sorghum fields where invading adult moths become attracted to chemicals emitted by the grasses themselves instead of landing on the maize or sorghum plants. These grasses provide the "pull" in the "push-pull" strategy.
They also serve as a refuge for the borers' natural enemies. Good trap crops include well-known grasses such as Napier grass (Pennisetum purpureum) and Sudan grass (Sorghum vulgare sudanense). Napier grass has a particularly clever way of defending itself against the pest onslaught: once attacked by a borer larva, it secrets sticky substance that physically traps the pest and effectively limits its damage. The "push" in the intercropping scheme is provided by the plants that emit chemicals which repel stemborer moths and drive them away from the main crop (maize or sorghum). The best candidates discovered so far with the repellent properties are members of leguminous genus Desmodium spp. whichis planted in between the rows of maize or sorghum. Being low-growing plant it does not interfere with the crops' growth and furthermore has the advantage of maintaining soil stability and improving soil fertility through nitrogen-fixation. It also serves as a highly nutritious animal feed and effectively suppresses Striga. Another plant showing good repellent properties is molasses grass (Melinis minutiflora), a nutritious animal feed with tick-repelling and stemborer larval parasitoid attractive properties.
Where farmers have been able to maintain their traditional cultivation, we can compare yields with the push-pull yields. The figure below (from Hassanali et al., 2008) shows yield differences in push–pull and control plots in 14 districts in Kenya during the 2005 long rains. Within a district bars marked by an asterisk are significantly lower ( P = 0.05, t-test):
Z.R. Khan, J.A. Pickett, A. Hassanali, A.M. Hooper and C.A.O. Midega (2008) Desmodium species and associated biochemical traits for controlling Striga species: present and future prospects. Insights. European Weed Research Society Weed Research 48, 302-306.
Z.R. Khan, C.A.O. Midega, E.M. Njuguna, D.M.Amudavi, J.W. Wanyama and J.A. Pickett (2008) Economic performance of the 'push-pull' technology for stemborer and Striga control in smallholder farming systems in western Kenya. Crop Protection 27, 1084-1097.(doi:10.1016/j.cropro.2008.01.005).
C.A.O. Midega, Z.R. Khan, J. van den Berg, C.K.P.O. Ogol, A.S. Dippenaar-Schoeman, J.A. Pickett and L.J. Wadhams (2008) Response of ground-dwelling arthropods to a ‘push-pull’ habitat management system: spiders as an indicator group. Journal of Applied Entomology 132, 248-254.
Z.R. Khan, D.M. Amudavi, C.A.O. Midega, J.M. Wanyama and J.A. Pickett (2008) Farmers’ perceptions of a ‘push-pull’ technology for control of cereal stemborers and Striga weed in western Kenya. Crop Protection 27, 976-987.
Z.R. Khan, C.A.O. Midega, D.M. Amudavi, A. Hassanali and J.A. Pickett (2008) On-farm evaluation of the ‘push-pull’ technology for the control of stemborers and striga weed on maize in western Kenya. Field Crops Research 106, 224-233.
A. Hassanali, H. Herren, Z.R. Khan, J.A. Pickett and C.M. Woodcock (2008) Integrated pest management: the push-pull approach for controlling insect pests and weeds of cereals, and its potential for other agricultural systems including animal husbandry. Philosophical Transactions of the Royal Society London B 363, 611-621.
S.M. Guchu, A. Yenesew, M.K. Tsanuo, N.K. Gikonyo, J.A. Pickett, A.M. Hooper and A. Hassanali (2007) C-methylated and C-prenylated isoflavonoids from root extract of Desmodium uncinatum. Phytochemistry 68, 646-651.
Z.R. Khan, C.A.O. Midega, A. Hassanali and J.A. Pickett (2007) Field developments on Striga control by Desmodium intercrops in a “push-pull” strategy. In: Integrating New Technologies for Striga Control: Towards Ending the Witch-hunt, pp. 241-252. Editors G. Ejeta and J. Gressel. (World Scientific, Singapore, New Jersey, London).
J.A. Pickett, Z.R. Khan, A. Hassanali and A.M. Hooper (2007) Chemicals involved in post-germination inhibition of Striga by Desmodium: opportunities for utilizing the associated allelopathic traits. In: Integrating New Technologies for Striga Control: Towards Ending the Witch-hunt, pp. 61-70. Editors G. Ejeta and J. Gressel. (World Scientific, Singapore, New Jersey, London).
Z.R. Khan, C.A.O. Midega, L.J. Wadhams, J.A. Pickett and A. Mumuni (2007) Evaluation of Napier grass (Pennisetum purpureum) varieties for use as trap plants for the management of African stemborer (Busseola fusca) in a push-pull strategy. Entomologia Experimentalis et Applicata 124, 201-211.
H.M. Mohamed, Z.R. Khan, J.M. Mueke, A. Hassanali, E. Kairu and J.A. Pickett (2007) Behaviour and biology of Chilo partellus (Swinhoe) on Striga hermonthica (Del.) Benth. infested and uninfested maize plants. Crop Protection 26, 998-1005.
Z.R. Khan, C.A.O. Midega, A. Hassanali, J.A. Pickett and L.J. Wadhams (2007) Assessment of different legumes for the control of Striga hermonthica in maize and sorghum. Crop Science 47, 728-734.
Cook, S.M., Khan, Z.R., Pickett, J.A. The use of push-pull strategies in integrated pest management (2007) Annu. Rev. Entomol., 52: 375-400.
Z.R. Khan, C.A.O. Midega, A. Hassanali, J.A. Pickett, L.J. Wadhams and A. Wanjoya (2006) Management of witchweed, Striga hermonthica, and stemborers in sorghum, Sorghum bicolor, through intercropping with greenleaf desmodium, Desmodium intortum. International Journal of Pest Management 52, 297-302.
Birkett, M.A., Chamberlain, K., Khan, Z.R., Pickett, J.A., Toshova, T., Wadhams, L.J. and Woodcock, C.M. (2006) Electrophysiological responses of the lepidopterous stemborers Chilo partellus and Busseola fusca to volatiles from wild and cultivated host plants. Journal of Chemical Ecology 32, 2475-2487.
Kalule, T., Khan, Z.R., Bigirwa, G., Alupo, J., Okanya, S., Pickett, J.A., Wadhams, L.J. Farmers' perceptions of importance, control practices and alternative hosts of maize stemborers in Uganda (2006) Int. J. Tropical Insect Sci., 26: 71-77.
Khan, Z.R., Pickett, J.A., Wadhams, L.J., Hassanali, A., Midega, C.A.O. Combined control of Striga hermonthica and stemborers by maize-Desmodium spp. intercrops (2006) Crop Prot., 25: 989-995.
Chamberlain, K., Khan, Z.R., Pickett, J.A., Toshova, T., Wadhams, L.J. Diel periodicity in the production of green leaf volatiles by wild and cultivated host plants of stemborer moths, Chilo partellus and Busseola fusca (2006) J. Chem. Ecol., 32: 565-577.
Midega, C.A.O., Khan, Z.R., Van Den Berg, J., Ogol, C.K.P.O., Pickett, J.A., Wadhams, L.J. Maize stemborer predator activity under 'push-pull' system and Bt-maize: A potential component in managing Bt resistance (2006) Int. J. Pest Man., 52: 1-10.
Tsanuo, M.K., Hassanali, A., Hooper, A.M., Khan, Z., Kaberia, F., Pickett, J.A., Wadhams, L.J. Isoflavanones from the allelopathic aqueous root exudate of Desmodium uncinatum (2003) Phytochemistry, 64: 265-273.
Gohole, L.S., Overholt, W.A., Khan, Z.R., Pickett, J.A., Vet, L.E.M. Effects of molasses grass, Melinis minutiflora volatiles on the foraging behavior of the cereal stemborer parasitoid, Cotesia sesamiae (2003) J. Chem. Ecol., 29: 731-745.
Khan, Z.R., Hassanali, A., Overholt, W., Khamis, T.M., Hooper, A.M., Pickett, J.A., Wadhams, L.J., Woodcock, C.M. Control of witchweed Striga hermonthica by intercropping with Desmodium spp., and the mechanism defined as allelopathic (2002) J. Chem. Ecol., 28: 1871-1885.
Kimani, S.M., Chhabra, S.C., Lwande, W., Khan, Z.R., Hassanali, A., Pickett, J.A. Airborne volatiles from Melinis minutiflora P. Beauv., A non-host plant of the spotted stem borer (2000) J. Ess. Oil Res., 12: 221-224.
Khan, Z.R., Pickett, J.A., Van den Berg, J., Wadhams, L.J., Woodcock, C.M. Exploiting chemical ecology and species diversity: Stem borer and Striga control for maize and sorghum in Africa (2000) Pest Manag. Sci., 56: 957-962.