What is Push-Pull Technology?
At its core, push-pull technology is an innovative farming method designed to naturally manage pests without the need for harmful chemicals. The technique involves intercropping a main crop—like maize—with two additional plant types that serve specific roles in pest control: the push plants and the pull plants.
The push plants, typically Desmodium species, are intercropped within the main crop rows. These plants release natural chemicals that repel pests, “pushing” them away from the maize.
Around the edges of the field, the pull plants—often grasses like Brachiaria or Napier grass—attract pests away from the main crop by serving as more enticing hosts. This setup “pulls” the pests to the outer edges, where they can cause less harm.
This dual action creates a natural barrier that deters pests from attacking the maize, all while avoiding synthetic pesticides. Early forms of push-pull farming were investigated in Australia and the US over three decades ago1, but the technology is applied most successfully in sub-Saharan Africa. While several studies have already demonstrated the effectiveness of push-pull technology, most of this research has been conducted in controlled environments like laboratories or greenhouses2. Investigating the technology under real-world farming conditions presents additional challenges.
More than just a push plant
In the African context, maize is the primary crop benefiting from push-pull technology, with Desmodium spp. as the main push plant. As a legume, Desmodium offers several benefits:
Pest Repellence: Desmodium releases natural compounds that repel pests like stem borers, a notorious maize predator. This reduces pest numbers in the field and helps maintain crop health.
Weed Control: Desmodium also inhibits the growth of Striga, a parasitic plant that saps nutrients from maize. Compounds called flavonoids released by Desmodium prevent Striga seeds from germinating, thereby protecting the maize (DOI:10.1016/j.phytochem.2015.06.026).
Soil Fertility: Because Desmodium is a nitrogen-fixing plant, it enriches the soil, reducing the need for synthetic fertilizers—a significant advantage for nutrient-demanding crops like maize.
When paired with pull plants, such as Brachiaria or Napier grass, Desmodium and maize form a mutually supportive ecosystem, making the maize less susceptible to pest infestations and nutrient depletion.
Entering the maize field
A research team from various institutions across Africa and Europe led by Meredith C. Schuman from the University of Zurich, Switzerland, has done a large-scale field study under real-world conditions in Kenya, Rwanda, and Uganda3. They compared leaf samples from push-pull fields to leaf samples from traditional maize fields, in an untargeted approach, using high-resolution mass spectrometry. Their goal was to identify “bioactive compounds” that were more abundant in push-pull maize plants compared to traditional crops.
Uncovering Key Metabolites in Push-Pull Agriculture using SIRIUS
As this large-scale study encompassed different farmer-run fields with varying soil compositions, rainfall patterns, plant ages, and local maize varieties, a highly conservative approach was taken in the selection of metabolites, focusing only on those compounds with the strongest likelihood of relevance to the push-pull system. Seven distinct features with higher abundance in push-pull fields were identified. To analyze these compounds, the researchers employed SIRIUS (version 5.8.0) alongside its CANOPUS and CSI:FingerID modules. They used CANOPUS for assigning compound classes and CSI:FingerID to search molecular structure databases.
Among the seven features, only one metabolite (HMBOA-Glc) was successfully matched by spectral library (GNPS) and also confirmed by the CSI:FingerID results. The remaining six features had no spectral library matches. They shared the same retention time, suggesting they might originate from a single molecule. CSI:FingerID annotations pointed to HDMBOA-Glc as a common precursor. It annotates three of these features as adduct combinations, one as the deglycosylated form HDMBOA, and two as substructures of HDMBOA. To verify these results, the chromatographic peak containing these features was isolated, but the minimal amount of material obtained made the structural verification using NMR analysis challenging.
Role of Benzoxazinoides in Pest Defense
Benzoxazinoid glycosides have been well-documented as effective herbivore deterrents. When present in the aglycone form, HDMBOA is toxic to pests and can even reduce insect weight after ingestion4. However, in its glycosylated form (HDMBOA-Glc), the compound is not directly toxic to insects. The transformation from HDMBOA-Glc to the active HDMBOA form5 only occurs when plant tissue is damaged, triggering a defensive response that converts the glycosylated form into its toxic counterpart. This mechanism may allow the maize to deter herbivores as they feed, stopping them before they can inflict significant damage on the plant.
Interestingly, these two detected benzoxazinoid compounds were found exclusively in maize and were not detected in either the intercrop (Desmodium spp.) or the pull crops (such as Brachiaria and Napier grass), indicating that their production is specific to maize in the push-pull system. This selective response suggests that push-pull technology could bolster maize’s natural defenses through biochemical pathways enhanced by this integrated planting method.
Why Push-Pull Maize is More Resilient
One question remains: why would maize in push-pull fields produce more defense compounds when pest pressure is actually lower? The researchers propose that the presence of nitrogen-fixing Desmodium makes soil nutrients more available, allowing maize plants to invest in additional chemical defenses like benzoxazinoids. This nutrient boost may prepare maize for potential threats even when pests are less abundant. However, further research is needed to fully understand how these mechanisms interact in natural farming environments.
Discrepancies in the Greenhouse
Some controlled greenhouse studies have reported different results, showing lower levels of benzoxazinoids in maize intercropped with Desmodium. These discrepancies highlight the complexity of field studies, where real-world variables like soil composition, plant age, and environmental exposure come into play. Field-grown plants are exposed to natural pest pressures and environmental factors that are hard to replicate in a lab setting, underscoring the need for additional research to reconcile these findings.
Conclusion: The Power of Push-Pull Technology
For maize farmers, push-pull technology offers a sustainable solution to protect crops without relying on pesticides. Not only does this approach lead to healthier crops and better yields, but it also fosters biodiversity. Uncovering the exact biochemical and ecological mechanisms that drive these patterns will be crucial for understanding how push-pull systems can be optimized further.
- 1.Miller JR, Cowles RS. Stimulo-deterrent diversion: A concept and its possible application to onion maggot control. J Chem Ecol. Published online November 1990:3197-3212. doi:10.1007/bf00979619
- 2.Lang J, Chidawanyika F, Khan ZR, Schuman MC. Ecological Chemistry of Pest Control in Push-Pull Intercropping Systems: What We Know, and Where to Go? Chimia. Published online November 30, 2022:906. doi:10.2533/chimia.2022.906
- 3.Lang J, Ramos SE, Reichert L, et al. Push–Pull Intercropping Increases the Antiherbivore Benzoxazinoid Glycoside Content in Maize Leaf Tissue. ACS Agric Sci Technol. Published online September 24, 2024:1074-1082. doi:10.1021/acsagscitech.4c00386
- 4.Glauser G, Marti G, Villard N, et al. Induction and detoxification of maize 1,4‐benzoxazin‐3‐ones by insect herbivores. The Plant Journal. Published online October 4, 2011:901-911. doi:10.1111/j.1365-313x.2011.04740.x
- 5.Robert CAM, Mateo P. The Chemical Ecology of Benzoxazinoids. Chimia. Published online November 30, 2022:928. doi:10.2533/chimia.2022.928
