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Field Crops Research 106 (2008) 224–233 www.elsevier.com/locate/fcr

On-farm evaluation of the ‘push–pull’ technology for the control of stemborers and weed on in western Kenya Zeyaur R. Khan a,*, Charles A.O. Midega a, David M. Amudavi a, Ahmed Hassanali a, John A. Pickett b a International Centre of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya b Biological Chemistry Division, Rothamsted Research, Harpenden, UK Received 8 August 2007; received in revised form 1 December 2007; accepted 1 December 2007

Abstract The ‘push–pull’ technology is a novel pest management strategy developed for control of stemborers and striga weed, Striga hermonthica,in maize-based farming systems in eastern Africa, where maize is intercropped with , a forage legume, and Napier grass is planted as a border crop. Desmodium repels stemborer moths while Napier grass attracts them. Desmodium also suppresses the parasitic striga weed through a series of mechanisms ranging from shading to allelopathy through the root system. The technology is currently being disseminated among smallholder farmers in eastern Africa and adoption rates are rising. Our on-station studies have reported efficacy of this technology against the two pests resulting in increased grain yields. The current study was conducted between 2003 and 2006 in 14 districts in western Kenya to assess effectiveness of the technology under farmers’ own conditions. Twenty farmers from each district, who had adopted the technology, were randomly selected for the study. Each farmer had a set of two plots, a ‘push–pull’ and a maize monocrop. Seasonal data were collected on percentage of maize damaged by stemborers, the number of emerged striga, height and grain yields. Similarly, farmers’ perceptions on the benefits of the technology were assessed using a structured questionnaire. Stemborer damage and striga counts to maize plants were significantly lower in the ‘push–pull’ plots than in the maize monocrop plots. Similarly, maize plant height and grain yields were significantly higher in the former. Farmers rated the ‘push–pull’ technology significantly superior in having reduced stemborers and striga infestation rates and increased soil fertility and grain yields. These results demonstrate that the technology is equally effective in controlling both pests with concomitant yield increases under farmers’ conditions in the districts studied. # 2007 Elsevier B.V. All rights reserved.

Keywords: ‘Push–pull’; Maize; Striga; Stemborers; Pest management; Kenya

1. Introduction is important in addressing the widening gap between food supply and food demand in the region, with per capita production Increasing crop production is an important challenge in steadily declining, with grain yields of maize being generally addressing economic growth, alleviating poverty and arresting <1.0 t/ha (Jagtap and Abamu, 2003). environmental degradation over most of sub-Saharan Africa The natural resource base, an important capital to (SSA). Efficient production of maize (Zea mays L.) by smallholder farmers, is likely to be overexploited where smallholder farmers, the single most important food and cash production constraints are too high, purchased inputs or labour crop for millions of rural farm families in the predominantly are scarce or absent, or environmental factors are too erratically mixed crop-livestock farming systems in Africa (Romney et al., variable for secure investment. Stemborers and parasitic striga 2003), is central to this challenge. Enhancing technical efficiency weeds are the two major biotic constraints to increased cereal production in SSA. The two main stemborer species found in the region are Busseola fusca Fu¨ller (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). * Corresponding author at: International Centre of Insect Physiology and Ecology (ICIPE), P.O. Box 30772, Nairobi 00100, Kenya. Stemborer damage causes grain yield losses estimated at 10– Tel.: +254 59 22216–8; fax: +254 59 22190. 80% of the potential grain output, depending on the pest E-mail address: [email protected] (Z.R. Khan). population density and the phonological stage of the crop at

0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2007.12.002 Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233 225 infestation (Kfir et al., 2002). Effective control of stemborers is United Kingdom, in collaboration with other national partners difficult, largely due to the cryptic and nocturnal habits of the in the development of a ‘push–pull’ technology for stemborer adult moths and the protection provided by the host stem for control. immature pest stages (Ampofo, 1986). Moreover, the con- The ‘push–pull’, as a tool in integrated pest management, ventionally recommended chemical control strategies are often first conceived by Pyke et al. (1987), and later formalized by not practical and economical for smallholder farmers (Van den Miller and Cowles (1990), involves use of behaviour-modifying Berg and Nur, 1998), while effectiveness of some of the cultural stimuli to manipulate the distribution and abundance of a pest control methods, considered cheaper for resource constrained and/or beneficial insects for management of the pest (Cook farmers, is not empirically demonstrated (Van den Berg et al., et al., 2007). In a ‘push–pull’ strategy, pests are repelled or 1998). deterred away from the target crop (push) by stimuli that mask Plants belonging to genus Striga (Scrophulariaceae) host apparency. The pests are simultaneously attracted (pull) to comprise obligate root parasites of cereal crops that inhibit a trap crop where they are concentrated, leaving the target crop normal host growth via three processes, competition for protected (Cook et al., 2007; Hassanali et al., 2008). The ‘push– nutrients, impairment of photosynthesis (Joel, 2000) and a pull’ technology described herein involves intercropping maize phytotoxic effect within days of attachment to its hosts (Gurney with a repellent plant such as desmodium, Desmodium et al., 1999, 2006). Among the 23 species of striga prevalent in uncinatum Jacq., and planting an attractive trap plant such as Africa, Striga hermonthica is the most socio-economically Napier grass, Pennisetum purpureum Schumach, as a border important weed in eastern Africa (Gressel et al., 2004; Gethi crop around this intercrop. Gravid stemborer females are et al., 2005). In western Kenya, it is estimated that 76% of land repelled from the main crop and are simultaneously attracted to planted to maize and sorghum, (L.) Moench, the trap crop (Khan et al., 2000, 2001; Cook et al., 2007). is infested with S. hermonthica, causing up to 100% yield The technology, so far the most effective and indeed the only losses, equivalent to annual losses estimated at $40.8 million ‘push–pull’ strategy in practice by farmers (Cook et al., 2007; (Kanampiu et al., 2002). Moreover, maize plants infested by Hassanali et al., 2008), also enhances productivity of maize- striga has recently been found to be more preferred for egg- based farming systems through in situ suppression and laying by stemborer moths than uninfested maize plants elimination of striga, S. hermonthica (Khan et al., 2000, (Mohamed et al., 2007). S. hermonthica infestation continues to 2001, 2002). The striga control tactic is provided by extend to new areas in the region as farmers abandon heavily desmodium that acts through a combination of mechanisms, infested fields for new ones (Khan, 2002; Gressel et al., 2004). including abortive germination of S. hermonthica seeds that fail In order to alleviate striga scourge, a number of conventional to develop and attach onto the hosts’ roots (Khan et al., 2002; methods based on the principles of reducing striga seed bank in Tsanuo et al., 2003). the soil, preventing new seed production and spread from Both on-station and on-farm trials have shown that the infested to non-infested soils have been tried with some limited strategy is effective in controlling both pests, resulting in and localized success (Hess and Ejeta, 1992; Berner et al., significant grain yield increases (Khan et al., 2001; Midega 1995; Oswald, 2005). The more recent technology for et al., 2005; Khan and Pickett, 2004; Khan et al., 2006a,c,d). controlling striga through imapazyr herbicide-tolerant mutant The technology is currently being promoted by different maize (IR maize) has shown significant increase in maize yields agencies in eastern Africa and adoption rates are rising, with (Kanampiu et al., 2003). However, success of IR maize will figures >10,000 as of 2007 (Z. Khan, unpublished data). We depend on how widely it is adopted by resource-poor farmers in undertook a multi-season study in farmer-managed fields in striga-infested areas. Moreover, it does not address the problem western Kenya to assess the effectiveness of the technology for of stemborers, which are a major constraint in cereal farming in stemborer and striga control across different agro-ecologies, the region (Khan et al., 2006d). Most smallholder farmers do and whether farmers were realizing its intended benefits. This not actively control stemborers (Chitere and Omolo, 1993; would be important in enhancing the design, implementation Ebenebe et al., 2000). The uptake of most of the available and dissemination of the technology with farmer-driven approaches to control stemborers and striga has been limited research, development and extension. due to biological and socio-economic reasons (Van den Berg and Nur, 1998; Van den Berg et al., 1998; Ebenebe et al., 2000; 2. Materials and methods Oswald, 2005). Stemborers are polyphagous and attack a wide range of 2.1. Study sites cultivated and wild plants belonging to three families— Poaceae, Cyperaceae and Typhaceae (Khan et al., 1997b; Kfir The studies were conducted over varied number of cropping et al., 2002). Although most of these grasses are hosts for the seasons, ranging from three to seven, between 2003 and 2006 in stemborers and, indeed, elicit higher levels of oviposition than 14 districts in western Kenya: Bondo (08250 to 0820 S, 34800 to 348 maize, subsequent larval survival is poor (Khan and Pickett, 330 E), Bungoma (08 250 to 08 530 S, 348 210 to 358 040E), Busia 2004; Khan et al., 2006b; Van den Berg, 2006; Khan et al., and Teso (08 10 to 08 460 S, 338 540 to 348 260 E), Butere-Mumias 2007b). These properties have been studied and exploited by (08 090 to 08 200S, 348 290 to 348330E), Homabay (08 400 to 08 S scientists at the International Centre of Insect Physiology and and 08 to 348 500 E), Kisii (08 300 to 08580 S, 348 380 to 348 E), Ecology (ICIPE) in Kenya and Rothamsted Research in the Kuria (18 50–18 220 S, 348 220–348430 E), Migori (08 400 and 08 S 226 Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233 and 348 and 348 500 E), Rachuonyo (08 170 to 0 8 360 S, 34 8 260 E), of 60 kg/ha. Nitrogen was applied after thinning of maize, in Siaya (08 260 to 08 180 S, 338 580 to 348 330 E), Suba (08 200 to 08 form of calcium ammonium nitrate (CAN), at the rate of 60 kg/ 520 S, 348 Eto348 E), Trans Nzoia (08520 to 18180S, 348380 to ha. The plot size varied from farmer to farmer, ranging from 358230E), and Vihiga (348 300 to 358 00 E, 08 to 08 150 N), where 25 m by 25 m to 40 m by 40 m, but for each farmer in the study, the ‘push–pull’ technology is being introduced for adoption by the sizes of the ‘push–pull’ and control plots were of the same smallholder farmers. Both stemborers and striga are serious pests size. The spacing between these plots within a farmer’s field in all the districts except in Trans Nzoia where only maize ranged between 10 m and 20 m. Both ‘push–pull’ and control stemborers are biotic maize production constraints. In Trans plots were maintained throughout the study period and the Nzoia district, B. fusca is the major stemborer species attacking companion crops equally maintained between seasons. The maize, whereas in other districts a mixture of B. fusca and C. farmers made all crop management decisions such as planting, partellus are present. In all the districts, except Trans Nzoia weeding, fertilizer application and harvesting. where there is only one cropping season in a year (April– September), the studies covered both the long (March–August) 2.3. Stemborer and striga infestation and short (October–January) seasons each year. Stemborer and S. hermonthica infestation levels were 2.2. Plot layout and data collection assessed non-destructively (once in a cropping season), using methodologies adapted from Khan et al. (2006c,d). At 4 weeks In each district, 20 farmers were randomly selected from after emergence, 100 maize plants were randomly selected in those who had recently adopted the ‘push–pull’ technology to each plot and tagged for subsequent assessments. At 10 weeks participate in the study. First, a checklist was made from a after emergence, the number of tagged plants with character- survey of all farmers who had recently adopted the technology istic ‘window-paned’ and ‘pin-holed’ leaves, and/or dead- and had experience of two to three cropping seasons. Through a hearts arising from stemborer larval feeding (Ampofo, 1986) structured questionnaire they were asked whether they were was recorded. This damage was expressed as the percentage of willing to participate in a long-term study assessing the pest maize plants damaged by stemborers. Similarly, the number of management efficiency of the technology on their farms. Each emerged S. hermonthica plants was counted from the tagged of the farmers had a set of two similar plots, a ‘push–pull’ plot plants during the same sampling occasion from within a radius and a maize monocrop plot, both with same level of striga and of 15 cm around the base of each plant. The data were soil fertility status at the time of establishment. As a general expressed as the number of emerged S. hermonthica per 100 practice in the dissemination of the ‘push–pull’ technology, plants. farmers are guided by the Ministry of Agriculture and ICIPE field staff. This is to ensure that the ‘push–pull’ plots are 2.4. Maize plant height and grain yields properly laid out and companion plots properly established and managed since the effectiveness of the technology is dependent At full physiological maturity, heights of the tagged plants on these two (Khan et al., 2007b). The ‘push–pull’ plot were measured and averaged for each plant and plot. All the comprised maize intercropped with desmodium, with three maize plants in each plot were then harvested and cobs sun- rows of Napier grass (Bana variety) planted around this dried separately for each plot and farmer. They were then intercrop at a spacing of 50 cm within and 50 cm between rows. shelled and dried to 12% moisture content and grain weights The innermost row of Napier grass was spaced 1 m from the taken individually for each plot and farmer. Grain weights were first row of maize as is often the practice (Khan et al., 2001). then converted into tones/hectare. Maize grain yields in the Desmodium was planted in between each row of maize. In both ‘push–pull’ plots were calculated taking into account the entire plots maize was planted at inter and intra-row spacing of 75 cm plot including area occupied by Napier grass. and 30 cm, respectively. The number of seeds planted per hill varied from 2–3 but at 4 weeks after crop emergence thinning 2.5. Farmer perceptions on the technology’s attributes was done to one maize plant per hill. Desmodium, being a perennial crop, was simply cut back at the beginning of To assess farmers’ perceptions on any benefits realized subsequent cropping seasons to allow for planting of maize and following adoption of the ‘push–pull’ technology, interviews was trimmed again during weeding of maize, after which it was using a structured questionnaire were conducted in 12 districts left to spread and cover the ground for the multiple benefits of during the long rainy season of 2006. Sixty farmers were weed control, moisture retention and overall beneficial effects randomly selected and interviewed in each district where they on soil health (Khan et al., 2006a). Except for Trans Nzoia were asked to rate the ‘push–pull’ and maize monocrop plots, where farmers planted long maturity maize variety H614, the using a scale of 1–4 (1 = least effective; 4 = most effective), on recommended hybrid for the highland regions, farmers in the their effects on stemborers, S. hermonthica, soil fertility and other districts planted medium maturity hybrids WH502, grain yields. Interviews were conducted following methodol- WH505 or H513, suited for mid-altitude areas, have similar ogies of Nyeko et al. (2002), either at a farmer’s home or in their grain yield potential and are equally susceptible to both pests fields. Either way, because farmers’ fields were always nearby (Khan et al., 2006d). Phosphorus, in form of di-ammonium (less than 1 km from the homestead), it was possible to verify phosphate (DAP), was applied in each plot at planting at the rate the farmers’ responses with field observations. Table 1 Mean (S.E.) seasonal percentagea of maize plants damaged by stemborer larvae at 10 weeks after crop emergence in plots of maize planted in sole stands (monocrop–mm) or in ‘push–pull’ (pp)

District Cropping seasons 224–233 (2008) 106 Research Crops Field / al. et Khan Z.R. Long rains 2003 Short rains 2003 Long rains 2004 Short rains 2004 Long rains 2005 Short rains 2005 Long rains 2006 mm pp mm pp mm pp mm pp mm pp mm pp mm pp Suba 10.7 (3.0) 2.4 (0.8) 37.6 (2.3) 9.8 (1.1) 22.7 (1.0) 7.8 (0.6) 25.7 (6.7) 5.0 (0.9) 20.5 (1.0) 3.6 (0.4) 25.8 (1.4) 6.1 (0.7) 18.2 (1.2) 4.0 (0.6) Bungoma 27.8 (1.2) 6.5 (0.7) 33.1 (1.8) 11.4 (2.0) 19.6 (1.0) 5.8 (0.5) 20.4 (1.0) 5.5 (0.3) 12.6 (1.0) 5.1 (0.6) 19.2 (0.9) 9.7 (0.8) 14.9 (0.7) 6.2 (0.4) Vihiga 28.2 (1.5) 14.6 (1.6) 34.7 (2.4) 17.9 (1.0) 2.1 (1.1) 1.0 (0.2) 3.7 (0.4) 0.9 (0.2) 15.3 (1.0) 5.6 (0.4) 17.2 (2.2) 7.1 (0.7) 2.6 (0.6) 0.6 (0.2) Busia 55.8 (5.8) 12.9 (2.1) 45.7 (4.1) 10.5 (2.6) 10.3 (1.2) 4.2 (0.8) 22.0 (1.8) 8.5 (0.9) 15.2 (1.2) 5.1 (1.2) 22.5 (1.4) 9.0 (1.2) 12.5 (1.2) 4.9 (0.5) Rachuonyo 4.4 (1.6) 0.5 (0.3) 19.1 (2.6) 4.6 (2.3) 18.0 (1.0) 4.7 (0.8) 11.8 (0.7) 1.0 (0.4) 2.7 (1.2) 0.0 4.9 (0.8) 0.9 (0.3) 9.5 (0.9) 1.3 (0.4) Migori 8.3 (1.3) 3.2 (0.7) 23.0 (1.7) 5.6 (2.3) 31.0 (1.7) 15.7 (1.3) 38.6 (2.1) 21.6 (1.2) 28.0 (1.8) 5.3 (0.4) 28.0 (1.4) 7.1 (0.7) 29.2 (2.6) 7.6 (1.1) Homabay 10.9 (0.5) 7.6 (0.5) 17.7 (2.7) 6.3 (0.3) 15.5 (0.6) 10.6 (1.5) 12.1 (0.7) 5.8 (0.3) 11.7 (0.8) 4.4 (0.4) 11.4 (0.8) 3.6 (0.2) 10.2 (0.4) 2.9 (0.2) Kisii 11.9 (1.1) 4.0 (0.6) 42.2 (3.4) 8.1 (1.2) 16.3 (2.9) 5.6 (0.9) 9.1 (2.0) 3.0 (0.7) 10.2 (1.1) 3.3 (0.5) 12.1 (1.5) 4.7 (0.8) 15.9 (2.1) 8.0 (1.3) Siaya 31.2 (1.1) 17.8 (0.8) 34.3 (1.0) 16.0 (1.5) 4.2 (0.4) 1.6 (0.4) 8.6 (1.2) 2.4 (0.3) 9.5 (1.5) 3.0 (0.5) 15.0 (1.5) 3.3 (0.4) 24.5 (1) 4.5 (0.4) T. Nzoia 24.7 (2.1) 13.1 (1.9) *a *a 19.0 (0.9) 6.8 (0.4) *a *a 15.4 (1.0) 5.6 (0.3) *a *a 20.2 (0.8) 6.9 (0.3) Kuria * * * * 14.2 (2.0) 8.6 (1.0) 15.4 (0.9) 3.4 (0.6) 30.9 (1.7) 4.1 (0.5) 31.2 (1.4) 1.3 (0.3) 15.9 (3.5) 0.1 (0.1) Teso * * * * * * * * 12.6 (0.5) 5.0 (0.6) 13.4 (1.4) 5.1 (1.0) 23.2 (0.8) 10.5 (0.6) Butere * * * * * * * * 31.3 (2.9) 6.2 (1.3) 32.8 (2.4) 6.8 (0.7) 38.9 (1.8) 11.6 (1.0) Bondo * * * * * * * * 14.0 (2.2) 8.3 (1.7) 4.2 (0.7) 4.1 (0.4) 3.0 (0.3) 1.4 (0.3) In all districts and seasons, except Vihiga during the long rainy season of 2004 and Bondo during the short rainy season of 2005, proportions of maize damaged by stemborers were significantly lower in the ‘push–pull’ than in the maize monocrop plots ( p < 0.05, t-test). Means represent data averages of 20 farmers in each district. T. Nzoia, Trans Nzoia; *a, no short rainy season in Trans Nzoia district; *, before technology was introduced in the district. a Counted from 100 tagged maize plants. 227 228 Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233

2.6. Data analysis

Data were averaged for each treatment and cropping season. A two-sample t-test (SAS Institute, 2002) was used to assess within- and multi-season effects of treatment on S. hermonthica counts and percentage of plants damaged by stemborer larvae as well as maize plant height and grain yields. Similarly, a two- sample t-test was used to compare farmers’ ratings of both cropping systems on the pests, soil fertility and grain yields. Because of the high variability observed for the actual S. hermonthica counts, log10[n + 1] transformations of the original data were performed. Similarly, the data on plants damaged by stemborers were subjected to arcsine transforma- tion prior to analysis. The significance level was set at a = 0.05 for all analyses. Untransformed means are presented in tables.

3. Results

3.1. Stemborer and striga infestation -test). Means represent data averages of 20 farmers in each district. *, before There were significantly lower proportions of stemborer- t damaged maize plants in the ‘push–pull’ than in the monocrop 0.05, < plots in all the districts during the entire study period ( p < 0.05, p t-test), except in Vihiga and Bondo during the long rainy season of 2004 and the short rainy season of 2005, respectively, ( p > 0.05, t-test), when infestation rates were generally low (Table 1). Within-season infestation rates in the maize monocrop plots ranged between 2.1% in Vihiga during the long rainy season of 2004 and 55.8% in Busia in the long rainy season of 2003. On the other hand, these rates ranged between 0% in Rachuonyo in the long rainy season of 2005 and 21.6% in Migori during the short rainy season of 2004 in the ‘push–pull’ plots. Seasonally, thus, there were reductions in infestation rates of between 2% in Bondo during the short rainy season of 2005 and 100% in Rachuonyo during the long rainy season of 2005 in the ‘push–pull’ plots. In both cases, however, the infestation rates were very low, otherwise in most of the districts the reductions in stemborer infestation rates ranged between 40% and 80% (Table 1). S. hermonthica counts were similarly significantly lower in the ‘push–pull’ than in the maize monocrop plots in all the in plots of maize planted in sole stands (monocrop–mm) or in ‘push–pull’ (pp) at 10 weeks after crop emergence a districts during the entire study period (p < 0.05, t-test) (Table 2).

Seasonal actual S. hermonthica counts per 100 maize plants counts ranged between 12 in Homabay during the short rainy season of 2004 and 1686 in Busia during the long rainy season of 2006 in the maize monocrop. On the other hand, the numbers ranged counts were significantly lower in the ‘push–pull’ than in the maize monocrop plots ( between 0 and 433 in Bungoma and Vihiga during the long rainy season of 2003, respectively, in the ‘push–pull’ plots (Table 2). Overall, there were reductions in S. hermonthica infestations in Striga hermonthica the ‘push–pull’ plots of between 50% in Homabay during the S. hermonthica long rainy season of 2004 and 100% in Bungoma during the long rainy season of 2003) (Table 2). Long rains 2003mm Short rains pp 2003 Long mm rains 2004 pp Short rains 2004 mm Long rains 2005 pp Short rains 2005 mm Long rains 2006 pp mm pp mm pp mm pp 3.2. Maize plant height and grain yields S.E.) actual seasonal

The lower stemborer and S. hermonthica infestation rates in Number of striga per 100 maize plants a Table 2 Mean ( the introduction of the technology in the districts. ‘push–pull’ plots were associated with consistent and District Cropping season SubaBungomaVihigaBusia 188 (45)Rachuonyo 132 (42)Migori 1261 (254) 190Homabay (17) 0 16 193 (0) 433 (8)Kisii (35) (135)Siaya 800 476 13 (272) 540 (170) (3)Kuria (172) 271 461 29 (25) (49) (9)Teso 283 170 (91) 140 (78) (64)Butere 284 325 (83) (48) 600Bondo 10 (68) 211 (2) 2 (59) 393 301 (1) 386 (46) (101) (176)In 27 all districts 28 (10) * and 197 (8) seasons, 266 (59) (66) 151 30 (16) 12 (10) 52 (2) 3 * (9) (3) * 409 568 49 (55) (89) 463 (9) * (109) 38 125 (7) 354 (25) 575 4 (43) (56) (1) * 121 118 (29) (53) 26 (6) 159 (45) 13 91 * 231 (3) 56 (17) (27) (16) * 98 336 876 (7) (47) (93) * 196 (34) 561 (38) 9 602 12 (3) 42 (73) (1) (23) 26 * (5) 11 77 (3) (9) 102 68 (11) (17) * 88 (24) * 190 (34) 6 4 284 (1) 486 (1) * (29) 177 (40) 516 477 (28) (64) (96) 171 (29) 9 * (2) 14 81 (2) 257 18 12 (10) 60 90 (47) (14) (3) (10) (31) 32 * (6) * 174 (28) 206 317 764 * 494 (20) 74 (43) (120) 119 (60) (26) 23 (10) 5 (13) (2) 315 (49) 99 205 (44) 20 26 7 (27) 91 (3) (3) (2) (24) * 4 * (1) 2 1686 28 67 (1) (166) (15) (17) * 409 16 (41) (3) 365 142 (44) (23) 98 (16) 276 143 (53) 231 (9) (50) 3 42 (1) (7) 142 * (20) * 30 12 (9) (3) 4 * 8 (1) (2) 23 2 (7) (4) 68 (16) 9 (1) * 215 * (26) 4 15 (2) * (4) 6 (2) * 43 (4) * 223 (19) * 1384 (74) 620 7 1 (99) (3) (1) 610 220 (98) (63) 150 (37) 280 161 760 (22) (30) (68) 297 (40) 135 (12) 8 (2) 3 79 (1) (11) 18 (4) 301 525 (23) (65) 774 (91) 112 168 (17) (19) 192 (44) Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233 229

Table 3 Mean ( S.E.) heightsa of maize plants (cm) at harvest in plots of maize planted in sole stands (monocrop–mm) or in ‘push–pull’ (pp) Districts Long rains 2005 t-Value p-Value Short rains 2005 t-Value p-Value Long rains 2006 t-Value p-Value mm pp mm pp mm pp Suba 116.2 (3.4) 171.5 (2.0) 14.5 <0.01 116.5 (2.7) 161.7 (1.2) 15.6 <0.01 135.9 (2.5) 195.8 (2.8) 15.5 <0.01 Bungoma 157.5 (2.2) 192.7 (2.0) 12.5 <0.01 120.4 (2.7) 141.8 (3.2) 5.1 <0.01 166.9 (2.3) 196.1 (2.6) 9.3 <0.01 Vihiga 163.8 (7.1) 210.7 (5.8) 5.1 <0.01 151.8 (5.8) 202.0 (5.7) 6.2 <0.01 164.7 (3.1) 220.7 (3.7) 11.5 <0.01 Busia 175.2 (5.4) 216.1 (5.3) 5.4 <0.01 112.4 (5.2) 183.8 (5.4) 9.6 <0.01 133.1 (5.5) 213.6 (4.9) 10.9 <0.01 Rachuonyo 145.9 (7.6) 204.6 (4.8) 12.2 <0.01 154.4 (10.5) 202.1 (5.5) 4.1 <0.01 172.5 (9.5) 212.4 (4.3) 10.9 <0.01 Migori 104.9 (3.2) 182.9 (2.6) 26.9 <0.01 101.9 (1.3) 183.7 (1.7) 56.7 <0.01 109.1 (2.4) 196.8 (1.5) 30.9 <0.01 Homabay 125.1 (10.7) 201.4 (5.8) 6.27 <0.01 114.3 (2.9) 197.3 (3.2) 18.9 <0.01 112.3 (4.4) 210.2 (2.6) 18.9 <0.01 Kisii 129.8 (9.7) 197.6 (4.2) 2.6 0.01 118.1 (3.2) 187.4 (2.7) 2.2 0.03 108.4 (8.6) 204.8 (7.6) 2.3 0.03 Siaya 128.5 (4.4) 204.8 (7.7) 6.3 <0.01 100.2 (15.9) 208.6 (8.1) 3.3 <0.01 116.7 (7.4) 214.9 (5.4) 9.6 <0.01 Kuria 99.4 (1.4) 202.5 (1.4) 52.5 <0.01 96.9 (1.6) 193.3 (1.4) 44.1 <0.01 102.3 (1.6) 202.2 (5.3) 17.9 <0.01 Teso 70.5 (2.3) 196.4 (12.1) 10.2 <0.01 88.9 (3.7) 132.4 (5.5) 6.5 <0.01 96.9 (3.9) 225.9 (3.2) 25.4 <0.01 Butere 120.7 (6.1) 202.6 (3.7) 11.4 <0.01 126.9 (4.0) 203.8 (4.7) 12.5 <0.01 142.8 (3.4) 196.5 (2.2) 13.1 <0.01 Bondo 117.9 (7.5) 171.6 (6.7) 5.3 <0.01 125.1 (4.7) 191.4 (3.7) 11.0 <0.01 167.3 (5.5) 215.4 (3.3) 7.5 <0.01 Means represent data averages of 20 farmers in each district. a Average of 100 maize plants. significantly taller maize plants (Table 3) and higher grain Multi-season analyses showed similar trends (Table 5), yields (Table 4) than in the monocrop plots in all the districts where in overall, the reductions in S. hermonthica counts in the and seasons ( p < 0.05, t-test). The average plant height in the ‘push–pull’ plots compared to the maize monocrop ranged maize monocrop plots ranged between 70.5 cm in Teso and between about 70% in Butere-Mumias and 95% in Kuria 175 cm in Busia during the long rainy season of 2005, districts. Reductions in stemborer infestations ranged between respectively. On the other hand, these ranged between 132.4 cm 46% in Teso and 90% in Rachuonyo. Similarly, increases in in Teso during the short rainy season of 2005 and 220.7 cm in plant height on the other hand ranged between 18% in Vihiga during the long rainy season of 2006 in the ‘push–pull’ Bungoma and 124% in Teso. Maize grain yield increases plots (Table 3). Thus the increases in plant height in the ‘push– ranged between 37% in Kisii and 129% in Kuria in the ‘push– pull’ plots compared to maize monocrop ranged between 1.2 pull’ plots (Table 5). times in Bungoma in the long rainy season of 2005 and more than twice in Siaya during the short rainy season of 2005. 3.3. Farmer perceptions on the technology’s attributes Within-season grain yields in the maize monocrop plots ranged between 0.5 t/ha in Rachuonyo during the short rainy season of The observations above corroborated the farmers’ percep- 2003 and 4.2 t/ha in Trans Nzoia during the long rainy season of tions on the efficacy of the technology on the target pests. The 2006. Conversely, in the ‘push–pull’ plots these ranged between farmers interviewed rated the ‘push–pull’ technology sig- 0.8 t/ha in Bondo and 5.8 t/ha in Butere-Mumias during the nificantly superior in reducing stemborer (all except Migori) short rainy season of 2005, respectively (Table 4). and S. hermonthica (all except Kisii) infestation and increasing

Table 4 Mean ( S.E.) grain yields of maize (t/ha) planted in sole stands (monocrop–mm) or in ‘push–pull’ (pp)

District Cropping season

Long rains 2003 Short rains 2003 Long rains 2004 Short rains 2004 Long rains 2005 Short rains 2005 Long rains 2006

mm pp mm pp mm pp mm pp mm pp mm pp mm pp

Suba 1.7 (0.2) 4.6 (0.2) 0.8 (0.2) 2.7 (0.3) 1.6 (0.1) 2.9 (0.2) 1.8 (0.1) 4.2 (0.1) 1.5 (0.1) 3.8 (0.1) 1.1 (0.1) 2.5 (0.1) 1.9 (0.1) 4.3 (0.1) Bungoma 2.6 (0.2) 5.4 (0.4) 2.4 (0.3) 5.0 (0.4) 2.1 (0.1) 4.8 (0.3) 1.7 (0.0) 3.2 (0.1) 2.8 (0.1) 4.5 (0.1) 1.2 (0.1) 2.1 (0.2) 2.7 (0.1) 3.8 (0.1) Vihiga 3.4 (0.6) 5.6 (0.7) 1.6 (0.1) 4.8 (0.7) 3.1 (0.4) 5.3 (0.3) 2.7 (0.3) 5.6 (0.3) 2.6 (0.2) 4.5 (0.3) 2.8 (0.2) 4.9 (0.1) 2.1 (0.1) 4.6 (0.2) Busia 3.3 (0.3) 5.4 (0.6) 2.3 (0.3) 3.7 (0.4) 1.9 (0.2) 4.1 (0.2) 2.0 (0.1) 4.2 (0.1) 2.7 (0.2) 5.6 (0.3) 2 (0.1) 3.4 (0.2) 2.5 (0.2) 5.2 (0.2) Rachuonyo 1.9 (0.2) 3.2 (0.3) 0.5 (0.0) 1.1 (0.1) 1.9 (0.2) 3.7 (0.3) 2.6 (0.1) 4.8 (0.1) 1.6 (0.1) 3.9 (0.2) 2.4 (0.3) 3.6 (0.3) 2.2 (0.2) 4.7 (0.2) Migori 2.9 (0.2) 4.1 (0.4) 3.7 (0.2) 4.7 (0.2) 2.7 (0.1) 4.4 (0.1) 2.1 (0.2) 4.1 (0.2) 1.7 (0.1) 3.6 (0.2) 0.8 (0.0) 3.0 (0.1) 1.5 (0.1) 4.2 (0.1) Homabay 3.3 (0.5) 4.6 (0.2) 2.1 (0.2) 2.6 (0.3) 1.6 (0.4) 3 (0.3) 2.3 (0.1) 3.2 (0.2) 2.2 (0.2) 4.3 (0.2) 1.2 (0.2) 2.5 (0.3) 2.2 (0.2) 4.3 (0.2) Kisii 2.7 (0.2) 4.4 (0.3) 2.2 (0.3) 3.2 (0.3) 2 (0.1) 2.6 (0.2) 3.2 (0.1) 4.3 (0.1) 3.7 (0.1) 4.4 (0.1) 3.3 (0.2) 4.2 (0.2) 3.1 (0.3) 4.5 (0.3) Siaya 2.1 (0.6) 3.2 (0.7) 1.9 (0.3) 3.3 (0.6) 2.3 (0.3) 3.4 (0.4) 1.3 (0.2) 2.3 (0.3) 1.7 (0.2) 2.9 (0.3) 2 (0.1) 4.2 (0.2) 1.8 (0.1) 4.7 (0.2) T. Nzoia 4.0 (0.2) 5.1 (0.3) *a *a 3.6 (0.1) 4.6 (0.1) *a *a 4.1 (0.1) 5.7 (0.1) *a *a 4.2 (0.1) 5.7 (0.1) Kuria * * * * 2 (0.1) 2.6 (0.2) 2.5 (0.1) 4.6 (0.2) 1.7 (0) 4.2 (0.1) 1.4 (0.0) 4.2 (0.1) 0.9 (0.3) 1.5 (0.1) Teso * * * * * * * * 1.1 (0.2) 3.8 (0.2) 0.9 (0.1) 1.9 (0.1) 2.3 (0.2) 3.9 (0.1) Butere * * * * * * * * 2.5 (0.1) 5.6 (0.2) 2.9 (0.1) 5.8 (0.1) 2.8 (0.1) 5.5 (0.2) Bondo * * * * * * * * 0.9 (0.3) 1.7 (0.2) 0.3 (0.1) 0.8 (0.1) 1.7 (0.1) 3.3 (0.2)

In all districts and seasons, maize grain yields were significantly higher in the ‘push–pull’ than in the maize monocrop plots ( p < 0.05, t-test). Means represent data averages of 20 farmers in each district. Key: as in Table 1. 230 Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233

Table 5 Multi-season analysis Districts Mean % stemborer t-Value Mean number of S. t-value Mean grain weight t-value Mean plant height t-value damaged plants hermonthica/100 (tones/ha) (cm) maize plants mm pp mm pp mm pp mm pp Suba 23 (1.5) 5 (0.5) 10.4 599 (29) 46 (5) 12.7 1.6 (0.1) 3.6 (0.1) 18.9 123 (2) 177 (2) 18.3 Bungoma 22 (0.6) 7 (0.3) 18.7 454 (8) 35 (6) 33.2 2.3 (0.1) 4 (0.1) 13.2 155 (2) 184 (3) 17.6 Vihiga 21 (0.9) 5 (0.5) 5.9 481 (43) 113 (19) 13.7 2.8 (0.1) 5.2 (0.1) 12.3 161 (3) 212 (3) 12.5 Busia 22 (1.6) 7 (0.5) 8.3 672 (74) 106 (17) 11.2 2.3 (0.1) 4.6 (0.1) 13.1 138 (5) 205 (4) 11.2 Rachuonyo 20 (0.7) 2 (0.3) 9.9 564 (17) 33 (6) 18.7 1.9 (0.1) 3.8 (0.1) 10.7 156 (6) 207 (4) 11.9 Migori 30 (1.0) 12 (0.7) 14.5 662 (71) 128 (16) 14.8 2.1 (0.1) 4 (0.1) 16.7 105 (2) 188 (3) 49.2 Homabay 28 (2.4) 5 (0.3) 14.2 460 (17) 40 (9) 15.6 2 (0.1) 3.6 (0.1) 10.0 117 (4) 203 (3) 19.4 Kisii 17 (1.7) 7 (0.8) 5.23 457 (13) 38 (8) 7.6 3 (0.1) 4.1 (0.1) 7.1 117 (4) 197 (3) 3.9 Siaya 17 (1.1) 5 (0.5) 9.9 446 (33) 100 (13) 9.03 2 (0.1) 4.4 (0.2) 10.7 115 (5) 208 (4) 10.7 Trans Nzoia 22 (1.0) 6 (0.5) 18.4 * * * 4.1 (0.1) 5.6 (0.1) 17.7 *a *a *a Kuria 23 (1.3) 3 (0.6) 14.8 511 (16) 24 (6) 20.7 1.7 (0.1) 3.9 (0.2) 10.2 99 (2) 199 (2.0) 47.4 Teso 17 (0.9) 7 (0.6) 9.2 761 (77) 184 (33) 7.7 1.6 (0.1) 3.9 (0.1) 14.7 86 (3) 193 (7.1) 14.1 B-Mumias 35 (1.4) 9 (0.7) 16.8 489 (51) 139 (14) 7.5 2.8 (0.1) 4.6 (0.1) 20.0 133 (3) 200 (2.0) 19.9 Bondo 25 (0.6) 8 (0.4) 2.3 578 (67) 154 (29) 7.9 1.2 (0.1) 2.5 (0.2) 5.5 149 (5) 203 (3.1) 9.6 Overall average 23 6.3 548.8 87.7 2.2 4.1 127.2 182.5 The t-values are associated with p < 0.01 in all cases. Key: pp–push–pull plots; mm–Maize monocrop. *No S. hermonthica in Trans Nzoia district; *a, data not taken because most of the plants lodged due to heavy winds before harvest; B-Mumias, Butere-Mumias.

Table 6 Farmer perceptions (ratings) on the benefits of the ‘push–pull’ technology following adoption Districts Ratings by farmers Cropping system Reduced stemborer Reduced striga Increased soil fertility Increased maize yield Mean (S.E.) t-Value Mean (S.E.) t-value Mean (S.E.) t-value Mean (S.E.) t-value Bungoma Push–pull 3.3 (0.1) 3.0 3.5 (0.1) 3.7 3.4 (0.1) 4.9 3.8 (0.1) 4.3 Monocrop 2.7 (0.2) p < 0.01 2.8 (0.2) p < 0.01 2.8 (0.1) p < 0.01 3.1 (0.1) p < 0.01 Busia Push–pull 3.5 (0.1) 5.4 3.3 (0.1) 4.1 3.2 (0.1) 1.9 3.8 (0.1) 5.9 Monocrop 2.7 (0.1) p < 0.01 2.6 (0.2) p < 0.01 3.1 (0.1) p = 0.06 2.7 (0.2) p < 0.01 Butere-Mumias Push–pull 3.3 (0.1) 3.5 3.1 (0.1) 5.6 3.1 (0.1) 7.7 3.5 (0.1) 5.1 Monocrop 2.7 (0.2) p < 0.01 2.1 (0.2) p < 0.01 2.0 (0.1) p < 0.01 2.4 (0.2) p < 0.01 Homabay Push–pull 3.1 (0.2) 7.1 3.2 (0.1) 9.1 3.4 (0.1) 9.0 3.5 (0.2) 5.9 Monocrop 1.7 (0.1) p < 0.01 1.5 (0.1) p < 0.01 1.9 (0.1) p < 0.01 2.1 (0.2) p < 0.01 Kisii Push–pull 3.3 (0.1) 2.3 2.8 (0.2) 1.8 3.0 (0.1) 2.8 3.4 (0.2) 2.1 Monocrop 2.9 (0.2) p = 0.03 2.4 (0.2) p < 0.08 2.6 (0.1) p = 0.01 2.9 (0.2) p = 0.04 Kuria Push–pull 3.4 (0.2) 3.8 3.3 (0.2) 4.0 3.5 (0.1) 8.5 4.0 (0.0) 8.6 Monocrop 2.3 (0.2) p < 0.01 2.0 (0.2) p < 0.01 2.1 (0.1) p < 0.01 2.2 (0.2) p < 0.01 Migori Push–pull 3.4 (0.1) 1.6 3.3 (0.1) 6.4 3.3 (0.1) 7.7 4.0 (0.0) 7.5 Monocrop 3.0 (0.1) p = 0.01 1.9 (0.1) p < 0.01 2.1 (0.1) p < 0.01 2.4 (0.2) p < 0.01 Rachuonyo Push–pull 3.0 (0.1) 2.6 3.0 (0.1) 3.6 2.9 (0.1) 3.2 3.1 (0.2) 2.6 Monocrop 2.7 (0.1) p < 0.01 2.2 (0.2) p < 0.01 2.3 (0.1) p < 0.01 2.6 (0.2) p = 0.01 Siaya Push–pull 3.6 (0.2) 3.8 3.5 (0.2) 4.7 3.3 (0.1) 7.6 3.7 (0.1) 5.0 Monocrop 2.4 (0.2) p < 0.01 2.2 (0.2) p < 0.01 1.8 (0.1) p < 0.01 2.7 (0.2) p < 0.01 Suba Push–pull 3.5 (0.1) 4.7 3.8 (0.1) 6.5 3.2 (0.1) 4.4 3.6 (0.2) 4.0 Monocrop 2.7 (0.1) p < 0.01 2.4 (0.2) p < 0.01 2.3 (0.1) p < 0.01 2.7 (0.2) p < 0.01 Vihiga Push–pull 3.7 (0.1) 9.5 3.8 (0.1) 8.5 3.6 (0.1) 9.5 4.0 (0.0) 13.9 Monocrop 1.8 (0.1) p < 0.01 2.3 (0.2) p < 0.01 2.1 (0.1) p < 0.01 1.9 (0.1) p < 0.01 Trans-Nzoia Push–pull 3.7 (0.1) 22.1 * * 3.3 (0.1) 16.1 4.0 (0.0) 33.6 Monocrop 1.6 (0.1) p < 0.01 * 1.7 (0.1) p < 0.01 1.6 (0.1) p < 0.01 Means represent data averages of 60 farmers in each district.*No S. hermonthica in Trans Nzoia district. Rating scale of 1–4 (1, least effective; 4, most effective). Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233 231 soil fertility (all except Busia) and maize grain yields (all the (scotophase) (Chamberlain et al., 2006), the period at which districts) (Table 6). The impact of ‘push–pull’ technology on stemborer moths seek host plants for oviposition (Pa¨ts, 1991). the four parameters was rated between 3.0 and 4.0 in all The amounts produced by maize over the same period, on the districts, except reduction in S. hermonthica infestation in Kisii other hand, only increased by about 10 times as much as in the and increase in soil fertility in Rachuonyo, which were rated 2.8 last hour of daytime (photophase) (Chamberlain et al., 2006). and 2.9, respectively. On the other hand, the rating of the maize Moreover, Napier grass produces higher levels of electro- monocrop on the parameters was mostly below 3.0 and in some physiologically active compounds than maize or sorghum instances as low as 1.5. (Birkett et al., 2006), which makes it more attractive than maize or sorghum. The green leaf volatiles produced by D. uncinatum 4. Discussion and conclusions on the other hand comprise such compounds as (E)-b-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene (Khan et al., 1997a, The results of the current study showed that the ‘push–pull’ 2000). These are semiochemicals produced during damage to technology described herein effectively controls both stem- plants by herbivorous insects (Turlings et al., 1990) and were borer and S. hermonthica, resulting in increases in maize grain shown to be repellent to ovipositing female moths but increased yields in farmer-managed fields across different agro-ecolo- foraging behaviour of stemborer parasitoids (Khan et al., gies. These results are comparable to those that have been 1997a, 2000). This combination thus ensures significantly reported from experimental plots at ICIPE’s Thomas Odhiambo fewer eggs are oviposited on the maize in the ‘push–pull’ plots Campus, western Kenya, where intercropping maize and than on the maize planted in sole stands. Furthermore, sorghum with Desmodium spp. gave effective control of both S. stemborer predators are more abundant and effective in the hermonthica and stemborers resulting in increase in maize ‘push–pull’ than in the maize monocrop plots, further reducing grain yields (Khan et al., 2000, 2001, 2002; Khan et al., pest populations in the former (Midega and Khan, 2003; 2006c,d; Khan et al., 2007a). Midega et al., 2006). The protection mechanism employed by D. uncinatum in S. In SSA, mixed crop-livestock systems predominate, and as hermonthica suppression has been established to involve a human population rises, land becomes an important constraint, combination of mechanisms, ranging from increased avail- necessitating further integration of the two enterprises, which ability of nitrogen, soil shading, to an allelopathic root must be supported by the small available landholdings (Khan exudation that is generated independently of the presence of S. and Pickett, 2004). The ‘push–pull’ technology thus compli- hermonthica (Khan et al., 2002). Exudates from D. uncinatum ments well the smallholder farmers’ mixed-cropping practice, roots possess germination stimulation and radical growth by enabling addition of livestock keeping, leading to an inhibition properties (Khan et al., 2002; Tsanuo et al., 2003) integrated crop-livestock system that combines both elements which interfere directly with parasitism and also diminish the of pest management and additional benefits, including fodder presence of S. hermonthica seeds through suicidal germination. production. Indeed in the high potential areas like Trans Nzoia This provides a novel means of in situ reduction of S. and Vihiga districts, the fodder component of the technology is hermonthica seed bank in the soil even in the presence of one of the main entry points for adopting ‘push–pull’ graminaceous host plants in the proximity (Khan et al., 2002). technology for most of the farmers. Additionally, because D. uncinatum is a perennial crop, it is Although not directly assessed in the current study, the able to exert its control effect on S. hermonthica even when the ‘push–pull’ technology also enhances soil integrity in a number host crop is out of season, an attribute that makes it a more of ways, such as through control of soil erosion and mitigation superior trap crop than most of the other legumes that have been of low and declining soil fertility status, another serious cereal reported to give only some limited level of striga control production constraint in SSA. Desmodium is an efficient (Oswald, 2005; Khan et al., 2007a). The results of the current legume in nitrogen fixation (Whitney, 1966) and studies have study thus demonstrate that these effects are achievable and reported significant increases in soil N in plots of maize sustainable under smallholder farmers’ management conditions intercropped with desmodium (Khan et al., 2006a). Through in the various districts. leaf fall, desmodium adds biomass to the soil thereby enhancing Stemborer control on the other hand is mediated by green soil organic matter (as suggested by Midega et al., 2005), and it leaf volatiles produced by the companion crops. Stemborer also conserves soil moisture (Khan et al., 2002). There is an moths prefer Napier grass to maize for oviposition, with overall increase in soil microbial and arthropod diversity and subsequent poor survival of the larvae (Khan et al., 2006b; Van activity in ‘push–pull’ plots (Midega and Khan, 2003; Khan den Berg, 2006; Van den Berg et al., 2006; Khan et al., 2007b). et al., 2006a). As has been observed by many researchers and The basis of this differential oviposition preference of practicing farmers, cropping practices that replenish and the moths for the wild host has been found to be linked to maintain high soil organic matter and also enhance the level the amounts and time of production of the green leaf volatiles, and diversity of soil macro and microbiota provide an the main cues used in host location by stemborer moths (Khan environment that through various processes enhances plant et al., 2000). The total quantities of the volatile chemicals health, leading to enhanced grain yields (Altieri and Nicholls, emitted by Napier grass, collected by air entrainment and 2003). Such soils also have fewer pest problems (Altieri, 1999). analyzed by gas chromatography, showed an increase of From the current study, majority of the farmers in the different approximately hundredfold in the first hour of nightfall districts observed an overall improvement in soil fertility status 232 Z.R. Khan et al. / Field Crops Research 106 (2008) 224–233 in their ‘push–pull’ plots and concomitant grain yield increases Ebenebe, A.A., Van den berg, J., Van der Linde, T.C., 2000. Farm management in addition to reduction in pest infestations. practices and farmers’ perceptions of stalk-borers of maize and sorghum in Lesotho. Int. J. Pest Manage. 47, 41–48. This is the first on-farm report of a combined control of both Gethi, J.G., Smith, M.E., Mitchell, S.E., Kresovich, S., 2005. Genetic diversity pests using a single method, with concomitant increases in of Striga hermonthica and Striga asiatica populations in Kenya. Weed Res. grain yields. These results, therefore, show that the technology 45, 64–73. has the potential to improve the livelihoods of smallholder Gressel, J., Hanafi, A., Head, G., Marasas, W., Obilana, A.B., Ochanda, J., farmers and rural families through increased agricultural Souissi, T., Tzotzos, G., 2004. Major heretofore intractable biotic con- straints to African food security that may be amenable to novel biotechno- productivity and improved environmental sustainability. In logical solutions. Crop Prot. 23, 661–689. addition, it opens up significant opportunities for smallholder Gurney, A.L., Press, M.C., Scholes, J.D., 1999. Infection time and density growth and represents a platform technology around which new influence the response of sorghum to the parasitic angiosperm Striga income generation and human nutritional components, such as hermonthica. New Phytol. 143, 573–580. livestock keeping, can be added. It therefore affords the Gurney, A.L., Slate, J., Press, M.C., Scholes, J.D., 2006. A novel form of resistance in to the angiosperm parasite Striga hermonthica.New smallholder farmers an opportunity to enter into cash economy. Phytol. 169, 199–208. For sustainability and wider dissemination of the technology, Hassanali, A., Herren, H., Khan, Z.R., Pickett, J.A., Woodcock, C.M., 2008. partnerships are being created to ensure concerted resource Integrated pest management: the push-pull approach for controlling insect mobilization, wider strategic collaborations and multidisci- pests and weeds of cereals, and its potential for other agricultural systems plinary linkages and participatory approaches in further including animal husbandry. Phil. Trans. R. Soc. B. 363, 611–621. Hess, D.E., Ejeta, G., 1992. Inheritance of resistance to Striga in sorghum research and development efforts as well as technology genotype SRN 39. Plant Breed. 109, 233–241. dissemination. We are currently assessing the economic Jagtap, S.S., Abamu, F.J., 2003. Matching improved maize production tech- benefits of the technology over the farmers’ own practices nologies to the resource base of farmers in a moist savanna. Agric. Syst. 76, and developing quality control protocols to monitor any 1067–1084. potential changes in allelopathic agents produced by desmo- Joel, D.M., 2000. The long-term approach to parasitic weed control: manip- ulation of specific developmental mechanisms of the parasite. Crop Prot. 19, dium roots and their effects on striga suppression and 753–758. elimination as well as the semiochemicals produced by the Kanampiu, F., Friesen, D., Gressel, J., 2002. CIMMYT unveils herbicide-coated Napier grass and desmodium in stemborer control. maize seed technology for Striga control. Haustorium 42, 1–3. Kanampiu,F.K.,Kabambe,V.,Massawe,C.,Jasi,L.,Friesen,D.,Ransom, Acknowledgements J.K., Gressel, J., 2003. Multi-site, multi-season field tests demonstrate that herbicide seed-coating herbicide-resistance maize controls Striga spp. and increases yields in several African countries. Crop Prot. 22, 697– The study was funded by the Gatsby Charitable Foundation, 706. UK and Kilimo Trust, East Africa, and conducted in collabora- Kfir, R., Overholt, W.A., Khan, Z.R., Polaszek, A., 2002. Biology and manage- tion with Rothamsted Research, which receives grant-aided ment of economically important lepidopteran cereal stemborers in Africa. support from the Biotechnology and Biological Sciences Annu. Rev. Entomol. 47, 701–731. Khan, Z.R., 2002. Cover crops. In: Pimentel, D. (Ed.), Encyclopedia of Pest Research Council (BBSRC) of the United Kingdom and Kilimo Management. Markel Dekker, Inc., USA, pp. 155–158. Trust. The farmers who allowed us to collect data in their farms, Khan, Z.R., Pickett, J.A., 2004. The ‘push–pull’ strategy for stemborer manage- and field assistance provided by Dickens Nyagol, Aloice Ndiege ment: a case study in exploiting biodiversity and chemical ecology. In: Gurr, and George Genga are greatly acknowledged too. G.M., Wratten, S.D., Altieri, M.A. (Eds.), Ecological Engineering for Pest Management: Advances in Habitat Manipulation for Arthropods. CABI Publishing, CABI, Wallingford, Oxon, United Kingdom, pp. 155–164. References Khan, Z.R., Ampong-Nyarko, K., Chilishwa, P., Hassanali, A., Kimani, S., Lwande, W., Overholt, W.A., Pickett, J.A., Smart, L.E., Wadhams, L.J., Altieri, M.A., 1999. The ecological role of biodiversity in agroecosystems. Woodcock, C.M., 1997a. Intercropping increases parasitism of pests. Nature Agric. Ecosyst. Environ. 74, 19–31. (London) 388, 631–632. Altieri, M.A., Nicholls, C.I., 2003. 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