Single-crop farming makes sense on paper. One crop to manage, one spray programme, one harvest schedule. Clean and simple.
The insect looking for your tomato, your cowpea, or your maize does not see it that way. It sees a field designed entirely around its needs. One host plant in every direction, uninterrupted, with no barriers, no competitors, no confusion. A monoculture field is not just easier to manage. It is easier to infest.
Intercropping, growing two or more crops together in the same field, makes the pest’s job harder. The mechanism behind why this works is not mystical. It is ecological. When a field contains multiple plant species with different scents, different structures, and different relationships with the insects around them, the pest faces obstacles that a monoculture never creates.
This article focuses specifically on intercropping combinations that have documented pest reduction benefits in West and East African farming conditions, what the evidence shows, and how to implement them practically on a small-scale farm.
The Push-Pull System: The Most Documented Intercropping Method in Africa
The push-pull system developed by the International Centre of Insect Physiology and Ecology in Kenya is the most extensively field-tested intercropping approach for pest management on the African continent. It has been adopted by over 200,000 farmers in Kenya, Uganda, Tanzania, and Ethiopia and has specific applicability for Nigerian and Ghanaian maize farmers facing stem borer and fall armyworm pressure.
The system works through two plant combinations used simultaneously.
Desmodium, specifically silverleaf Desmodium uncinatum or greenleaf Desmodium intortum, is planted as an intercrop between maize rows. Desmodium releases volatile compounds from its roots and above-ground parts that repel female stem borer and fall armyworm moths from landing on maize plants to lay eggs. This is the push component, pushing the pest away from the main crop. Desmodium also releases root exudates that suppress Striga weed, a major yield-reducing parasitic plant in maize fields across East Africa and parts of northern Nigeria.
Napier grass or Brachiaria grass is planted as a border crop around the outside of the maize field. It attracts stem borer moths through volatile compounds that mimic the signals from a highly suitable host plant. Moths attracted to the border grass lay eggs on it preferentially over the maize inside the field. The grass then produces a sticky substance when larvae attempt to bore into the stems that traps and kills them. This is the pull component.
The combined effect reported in Kenyan farmer trials is a reduction in stem borer damage of 80 to 87 percent compared to maize monoculture. Yield increases of 1 to 3.5 tonnes per hectare above monoculture yields have been recorded, with the additional benefit of Desmodium’s nitrogen fixation improving soil fertility simultaneously.
Intercropping Combinations for West African Vegetable Farmers
The push-pull system is the most researched example but the principle behind it applies broadly. Several intercropping combinations have demonstrated pest reduction benefits specifically relevant to vegetable farmers in Nigeria, Ghana, and neighbouring countries.
Tomato with African marigold
African marigold, Tagetes erecta, planted as a border or intercrop with tomato reduces whitefly populations through two mechanisms. Above ground, marigold releases limonene and other volatile terpenes that interfere with the host-location signals whiteflies use to find tomato plants. Below ground, marigold roots release thiophene compounds that are toxic to root-knot nematodes in the soil, addressing a secondary pest problem that commonly attacks tomato roots.
Plant two rows of marigold around the perimeter of each tomato bed and one row between every four tomato rows within the bed. This density is sufficient to create the volatile compound barrier that disrupts whitefly host-location without competing significantly with tomato for light and nutrients.
Cowpea with sorghum or millet
Cowpea grown alongside sorghum or millet benefits from partial physical shielding that reduces the rate at which bruchid beetles, the cowpea weevil, locate and colonise cowpea plants in the field. The taller cereal creates a broken visual and chemical landscape that slows the beetle’s efficient host-finding behaviour compared to a solid cowpea monoculture.
Sorghum also provides structural support for cowpea vines in some varieties, reducing the need for artificial staking while the mixed canopy suppresses weeds that would otherwise harbour aphid populations around cowpea plants.
Pepper with onion or garlic
The sulfur-containing volatile compounds released by allium family plants including onion, garlic, and shallots disrupt the chemical cues that aphids use to locate host plants. Pepper intercropped with onion at a ratio of three pepper plants to one onion plant in alternating rows shows consistent reduction in aphid colonisation pressure compared to pepper monoculture in field observations across Ogun, Oyo, and Nasarawa states in Nigeria.
The garlic border also deters the pepper weevil, Anthonomus eugenii, which uses olfactory cues to locate pepper plants. Disrupting those cues through the sulfur volatiles from garlic reduces weevil infestation rates on intercropped pepper compared to isolated monoculture plantings.
Amaranth as a trap crop near beans and cowpea
Amaranth planted as a dense border around bean or cowpea plots functions as a trap crop for leafminer flies, Liriomyza species, which attack legume foliage and cause significant cosmetic and functional damage. Leafminer flies preferentially select amaranth as an egg-laying site when it is available alongside legume crops.
The management protocol involves allowing the amaranth to grow alongside the legume crop throughout the season, monitoring the amaranth leaves for leafminer activity, and cutting and removing the amaranth from the field at the point when leafminer pupae are developing in the leaves but before adult flies emerge. This removes the leafminer population from the farm entirely at a vulnerable stage without any chemical input.
Practical Implementation on a Small Farm
The most common reason West and East African farmers do not adopt intercropping pest management combinations is not lack of knowledge. It is uncertainty about how to adjust planting density, spacing, and timing when two crops are sharing the same ground.
| Intercrop Combination | Row Spacing | Within-Row Spacing | Planting Timing |
|---|---|---|---|
| Maize with Desmodium | Plant Desmodium in every maize row gap at 50cm intervals | 30cm between Desmodium plants | Same day as maize or within 1 week |
| Tomato with marigold border | Marigold border at 30cm apart around bed perimeter | One marigold row between every 4 tomato rows | Transplant marigold 2 weeks before tomato |
| Cowpea with sorghum | Alternate 2 cowpea rows with 1 sorghum row | Standard spacing for each crop | Plant simultaneously |
| Pepper with onion | Alternate rows, 3 pepper to 1 onion | Standard for each crop | Plant onion 3 weeks before pepper |
| Bean with amaranth border | Amaranth border at 25cm apart | Dense border, 3 to 4 rows wide | Plant amaranth simultaneously with beans |
The yield of your primary crop will typically be slightly lower per unit area in an intercrop system compared to pure monoculture of that crop because of competition for light, water, and nutrients. This is a real trade-off that deserves honest acknowledgment. The benefit is reduced pest pressure, reduced chemical input cost, improved soil health from nitrogen-fixing companion plants, and a secondary crop yield from the intercrop plant that contributes to total farm income.
For most African smallholder farmers operating without crop insurance and with limited capacity to absorb a catastrophic pest-related crop failure, the stability that intercropping provides across seasons has greater financial value than the marginal yield increase of monoculture in a good season.
You can also read: Companion planting guide for West African vegetable farmers
Conclusion
Intercropping for pest management works because it uses ecology rather than fighting it. A diversified farm is a more complex environment that pest insects are less efficiently adapted to exploit than a simple monoculture.
You do not need to convert your entire farm to intercropping in one season. Start with one combination on one section of your farm this season. Observe the pest pressure, the weed suppression, and the overall crop performance compared to your monoculture plots. The results from that one trial will tell you more about whether and how to expand intercropping on your specific farm than any general recommendation can.
Single-crop farming makes sense on paper. One crop to manage, one spray programme, one harvest schedule. Clean and simple.
The insect looking for your tomato, your cowpea, or your maize does not see it that way. It sees a field designed entirely around its needs. One host plant in every direction, uninterrupted, with no barriers, no competitors, no confusion. A monoculture field is not just easier to manage. It is easier to infest.
Intercropping, growing two or more crops together in the same field, makes the pest’s job harder. The mechanism behind why this works is not mystical. It is ecological. When a field contains multiple plant species with different scents, different structures, and different relationships with the insects around them, the pest faces obstacles that a monoculture never creates.
This article focuses specifically on intercropping combinations that have documented pest reduction benefits in West and East African farming conditions, what the evidence shows, and how to implement them practically on a small-scale farm.
The Push-Pull System: The Most Documented Intercropping Method in Africa
The push-pull system developed by the International Centre of Insect Physiology and Ecology in Kenya is the most extensively field-tested intercropping approach for pest management on the African continent. It has been adopted by over 200,000 farmers in Kenya, Uganda, Tanzania, and Ethiopia and has specific applicability for Nigerian and Ghanaian maize farmers facing stem borer and fall armyworm pressure.
The system works through two plant combinations used simultaneously.
Desmodium, specifically silverleaf Desmodium uncinatum or greenleaf Desmodium intortum, is planted as an intercrop between maize rows. Desmodium releases volatile compounds from its roots and above-ground parts that repel female stem borer and fall armyworm moths from landing on maize plants to lay eggs. This is the push component, pushing the pest away from the main crop. Desmodium also releases root exudates that suppress Striga weed, a major yield-reducing parasitic plant in maize fields across East Africa and parts of northern Nigeria.
Napier grass or Brachiaria grass is planted as a border crop around the outside of the maize field. It attracts stem borer moths through volatile compounds that mimic the signals from a highly suitable host plant. Moths attracted to the border grass lay eggs on it preferentially over the maize inside the field. The grass then produces a sticky substance when larvae attempt to bore into the stems that traps and kills them. This is the pull component.
The combined effect reported in Kenyan farmer trials is a reduction in stem borer damage of 80 to 87 percent compared to maize monoculture. Yield increases of 1 to 3.5 tonnes per hectare above monoculture yields have been recorded, with the additional benefit of Desmodium’s nitrogen fixation improving soil fertility simultaneously.
Intercropping Combinations for West African Vegetable Farmers
The push-pull system is the most researched example but the principle behind it applies broadly. Several intercropping combinations have demonstrated pest reduction benefits specifically relevant to vegetable farmers in Nigeria, Ghana, and neighbouring countries.
Tomato with African marigold
African marigold, Tagetes erecta, planted as a border or intercrop with tomato reduces whitefly populations through two mechanisms. Above ground, marigold releases limonene and other volatile terpenes that interfere with the host-location signals whiteflies use to find tomato plants. Below ground, marigold roots release thiophene compounds that are toxic to root-knot nematodes in the soil, addressing a secondary pest problem that commonly attacks tomato roots.
Plant two rows of marigold around the perimeter of each tomato bed and one row between every four tomato rows within the bed. This density is sufficient to create the volatile compound barrier that disrupts whitefly host-location without competing significantly with tomato for light and nutrients.
Cowpea with sorghum or millet
Cowpea grown alongside sorghum or millet benefits from partial physical shielding that reduces the rate at which bruchid beetles, the cowpea weevil, locate and colonise cowpea plants in the field. The taller cereal creates a broken visual and chemical landscape that slows the beetle’s efficient host-finding behaviour compared to a solid cowpea monoculture.
Sorghum also provides structural support for cowpea vines in some varieties, reducing the need for artificial staking while the mixed canopy suppresses weeds that would otherwise harbour aphid populations around cowpea plants.
Pepper with onion or garlic
The sulfur-containing volatile compounds released by allium family plants including onion, garlic, and shallots disrupt the chemical cues that aphids use to locate host plants. Pepper intercropped with onion at a ratio of three pepper plants to one onion plant in alternating rows shows consistent reduction in aphid colonisation pressure compared to pepper monoculture in field observations across Ogun, Oyo, and Nasarawa states in Nigeria.
The garlic border also deters the pepper weevil, Anthonomus eugenii, which uses olfactory cues to locate pepper plants. Disrupting those cues through the sulfur volatiles from garlic reduces weevil infestation rates on intercropped pepper compared to isolated monoculture plantings.
Amaranth as a trap crop near beans and cowpea
Amaranth planted as a dense border around bean or cowpea plots functions as a trap crop for leafminer flies, Liriomyza species, which attack legume foliage and cause significant cosmetic and functional damage. Leafminer flies preferentially select amaranth as an egg-laying site when it is available alongside legume crops.
The management protocol involves allowing the amaranth to grow alongside the legume crop throughout the season, monitoring the amaranth leaves for leafminer activity, and cutting and removing the amaranth from the field at the point when leafminer pupae are developing in the leaves but before adult flies emerge. This removes the leafminer population from the farm entirely at a vulnerable stage without any chemical input.
Practical Implementation on a Small Farm
The most common reason West and East African farmers do not adopt intercropping pest management combinations is not lack of knowledge. It is uncertainty about how to adjust planting density, spacing, and timing when two crops are sharing the same ground.
| Intercrop Combination | Row Spacing | Within-Row Spacing | Planting Timing |
|---|---|---|---|
| Maize with Desmodium | Plant Desmodium in every maize row gap at 50cm intervals | 30cm between Desmodium plants | Same day as maize or within 1 week |
| Tomato with marigold border | Marigold border at 30cm apart around bed perimeter | One marigold row between every 4 tomato rows | Transplant marigold 2 weeks before tomato |
| Cowpea with sorghum | Alternate 2 cowpea rows with 1 sorghum row | Standard spacing for each crop | Plant simultaneously |
| Pepper with onion | Alternate rows, 3 pepper to 1 onion | Standard for each crop | Plant onion 3 weeks before pepper |
| Bean with amaranth border | Amaranth border at 25cm apart | Dense border, 3 to 4 rows wide | Plant amaranth simultaneously with beans |
The yield of your primary crop will typically be slightly lower per unit area in an intercrop system compared to pure monoculture of that crop because of competition for light, water, and nutrients. This is a real trade-off that deserves honest acknowledgment. The benefit is reduced pest pressure, reduced chemical input cost, improved soil health from nitrogen-fixing companion plants, and a secondary crop yield from the intercrop plant that contributes to total farm income.
For most African smallholder farmers operating without crop insurance and with limited capacity to absorb a catastrophic pest-related crop failure, the stability that intercropping provides across seasons has greater financial value than the marginal yield increase of monoculture in a good season.
You can also read: Companion planting guide for West African vegetable farmers
Conclusion
Intercropping for pest management works because it uses ecology rather than fighting it. A diversified farm is a more complex environment that pest insects are less efficiently adapted to exploit than a simple monoculture.
You do not need to convert your entire farm to intercropping in one season. Start with one combination on one section of your farm this season. Observe the pest pressure, the weed suppression, and the overall crop performance compared to your monoculture plots. The results from that one trial will tell you more about whether and how to expand intercropping on your specific farm than any general recommendation can.
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