Chapters 7.10
7.10 - Push-pull intercropping to reduce flying insects
Jade Muileboom, University of Guelph,Canada
Source:https://en.wikipedia.org/wiki/File:Maize-push-pull-farm-at-ICIPE,_Mbita_Point,_Kenya.jpg
Suggested citation for this chapter.
Author name (2022) title of chapter. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
The Problem
Cereal crops such as maize and sorghum are often targeted by various flying insect species that utilize the leaves to lay their eggs, leaving
behind a major pest once the eggs reach the larvae stage of development. The larvae quickly shred through the leaves burrowing into the stems (gaining the name stem borers) resulting in severe yield losses up to 80% and increased danger of lodging (Khan et al., 2008). Use of chemical pesticides is often not an option for subsistence farmers due to the cost, lack of supply and access to appropriate information.
Push-Pull system: How it works
Despite these concerns, the Push-Pull companion cropping system, offers a promising strategy for simultaneously targeting these pests as well as striga weed (Khan et al., 2014). By integrating a repellant companion crop (the push) and an attractive trap companion crop (the pull) the push-pull system can help redirect and terminate the life cycles of both Striga and stem borer populations. The most successful system uses two plant varieties, Desmodium (push plant) and Napier grass (pull plant). The sprawling perennial legume Desmodium has been found to release a leaf volatile repellant to moths and other flying insect species in the air as well as various phytochemicals into the soil that cause the initial germination and then death of Striga seeds (Van den Berg and Van Hamburg, 2015). On the other hand, the fast-growing Napier grass has been observed to be an attractive sink crop, drawing the adult flying insects to lay their eggs on the grass instead of the main cereal crop (Van den Berg and Hamburg, 2015). In addition to this redirection, the eggs, upon reaching the larvae stage and subsequently burrowing into the plant, become trapped and die within the sticky sap produced within the Napier grass stems (Khan et al., 2000). Napier grass has been observed to be effective trap plant for the Chilo partellus (Lepidoptera: Crambidae) and Busseola fusca (Fuller) (Lepidoptera: Noctuidae) insect species. To best utilize these capabilities, the push crop is planted between the main cereal crop and the pull variety bordering the main plot. Studies have found that fields which implemented this cropping method showed 18 times lower Striga and 6 times lower stemborer levels than the control fields (Midega et al., 2015).
Other Benefits
Aside from combating pests, Desmodium and Napier grass offer other soil, animal and financial benefits. For instance, Desmodium can be used for animal fodder and green manure, with studies linking its consumption to greater milk production in livestock (Khan et al., 2016). Also as a legume it can be used as a cover crop to add nitrogen to the soil while improving soil structure and preventing erosion (FAO, 2016) Napier grass can also be used for forage and is noted for its fast growth and high nutrient content (FAO, 2006; Rambau et al., 2016). It too can be used to prevent soil erosion particularly on hillside farmland (FAO, 2006). Excess cuttings from these varieties can be sold to neighbouring farmers as forage or for further propagation.
Field Prep and Planting
Proper land preparation is important factor in integrating push-pull system into pre-existing cropping systems. Napier Grass and Desmodium are both perennial companion crops, thus a thorough investment into full land preparation can translate to these varieties thriving for many years. A complete ploughing with subsequent disc-harrowing of the field and then drilling during the seeding stage is recommended (FAO, 2017). For Napier Grass, plant in furrows ~15 cm deep, covering with ~7.5cm of soil to start and adding more in as the plant grows (FAO, 2017). If available, first adding 2 handfuls of manure to the furrows is recommended to improve plant growth. The pull border should be planted at a distance of at least 1 m from the main cereal crop to prevent shading (Khan et al., 2001). Further, it is best to wait 12 weeks after sowing the main cereal crop before planting this boarder crop (FAO, 2006). Napier Grass while available in seed form is most commonly propagated from cuttings, splits or the whole stem. If planting from stem pieces, choose a piece with at least 3 nodes, one of which should remain exposed while the others are covered in soil (FAO, 2017).
Desmodium can be planted from cuttings or seed. Due to the small size of the desmodium seeds it is important that the soil be finely broken up (mixing the soil with finer soil or sand can help this process) before drill planting (CTA, 2007). Utilizing desmodium cuttings with a minimum of 2 internodes can be a quicker and easier mode of establishment provided the soil is sufficiently moist. The desmodium planting material should be placed in a 1-2 cm deep furrow ~30 cm away on either side from the closest cereal row (CTA, 2007; Khan et al., 2008).
Harvesting for Fodder
As rule of thumb Napier grass is best harvested when it reaches 1 m of height and is a rich green colour (FAO, 2006). Once the grass surpasses this height and reaches maturity the colour will begin to turn first to a pale green and then a yellow-green---a sign that the nutrient content and digestibility is decreasing (FAO, 2006; Rambau et al., 2016). One study in Kenya found that with good weather it tolerated defoliation every 6-8 weeks (FAO, 2006).
Challenges
While various research and farm trials have shown that the push-pull cropping system can reduce yield losses and create new financial opportunities for farmers, challenges remain in farmers’ integration and acceptance of it. Arguably, the initial cost, labour and material requirements are the greatest barriers to uptake. Desmodium and napier grass seeds are not always readable available or feasible for plot requirements. Plant cuttings which are often a quicker and more reliable way to propagate these varieties are also difficult to obtain, especially as proper storage and transport of these materials are generally unavailable (Turano et al., 2016). Much of current push-pull discourse suggests farmers buy them from neighbouring farms, which can be a limiting factor based on the present prevalence of push-pull farm systems. While the number of push-pull systems are increasing, the density of farms have not yet reached a level to ensure a steady supply to interested farmers.
Then, for those able to obtain the needed materials the setup of the push-pull plot can be intimidating as well. The plot requires various spacing, planting and maintenance practices to meet the needs of each variety, thus interested farmers will need to be properly informed and likely assisted in its construction (CGIAR, 2005). However, once properly instructed concerning the push-pull system, some studies have found that local farmers can make effective teachers for other farmers in their region, thus increasing local acceptance of the technology (Amudavi et al., 2009). It should also be noted that the high initial labour and material inputs decrease substantially in the following seasons as the push and pull companion crops are perennials (Khan et al., 2008). After the first year, the main remaining labour requirement is the maintenance of the companion crop lines to prevent undesired spread. Therefore, the first season is largely one of investment as the benefits of the system are not very evident till the second or third cropping season.
Napier grass and Desmodium plants while providing useful services, can be constrained by factors such as disease and nutrient deficiency. Herbivorous beetles are a concern for desmodium production while Napier grass is susceptible to both Head smut and Napier grass stunt disease---all of which have been linked to a significant decrease in yield (Lebesa et al., 2012; Asudi et al., 2015; FAO, 2017). Attention should be paid that napier grass is not planted too close to the main crop as competition for light and nutrients could become a problem (Sekiya et al., 2015). Napier grass does require a fair amount of water and nutrients from the soil which could be difficult to obtain in arid soils (FAO, 2017).
Future Opportunities for Companion Cropping and Plant Bioinsecticides
There remains a lot to be understood concerning companion crop interactions in regards to nutrient competition, pest management and yield effects. While current scientific research around physically integrating a diversity of companion plants remains limited, inquiry is increasing around the use of plant extracts or oils as bioinsecticides. Neem, Lemongrass and Rosemary oil are a few of many observed to have significant effects in managing and deterring pests (Kianmatee and Ranamukhaarachchi, 2007; Ben Issa et al., 2016). Thus, improving farmer understanding and access to plant oil extraction technologies could offer a viable solution to pest management and economic opportunity. Another area that companion crop interactions could be explored is in deterrence or trap mechanisms in local indigenous landraces. One study in Kenya found that local spider plant (Gynandropsis gynandra) in combination with green mulch and coriander was more effective at reducing Thrip prevalence and damage in snap bean than the conventional pesticide (Waiganjo et al., 2007).
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 8.10:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.10_south_asian.pdf
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 8.10:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.10e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 8.10:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.10subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 8.10:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.10latin_america.pdf
Source: MN Raizada and L Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
Further Practical Resources and Useful Reading
1). The CTA Practical Guide Series, No. 2: How to control Striga and stemborer in maize https://publications.cta.int/media/publications/downloads/1361_PDF.pdf
2). A primer on Planting and Managing ‘Push-Pull’ Fields for Stemborer and Striga Weed Control in Maize http://www.push-pull.net/step_step.pdf
3). Companion Planting & Botanical Pesticides: Concepts & Resources https://attra.ncat.org/attra-pub/viewhtml.php?id=72#2
References
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2. Asudi, G. O., van den Berg, J., Midega, C. A. O., Pittchar, J., Pickett, J. A., & Khan, Z. R. (2015). Napier grass stunt disease in East Africa: Farmers’ perspectives on disease management. Crop Protection, 71, 116–124. http://doi.org/10.1016/j.cropro.2015.02.008
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6. FAO. (2017a). Napier Grass Stunt. Retrieved March 3, 2017, from http://www.fao.org/Ag/agp/agpc/doc/Newpub/napier/napierstunt.htm
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