Botanical Pesticides

Lead Organization:

University of Greenwich

Partner Organizations:


Community of Practice:

East & Southern Africa, Farmer research network (FRN)


Malawi and Tanzania




Most smallholder farmers depend on agricultural produce for their livelihoods, making food security their most important consideration. Crop production and storage are limited by many constraints, with insect pests arguably the most important. If unmanaged, insect pests can cause significant yield loss. Commercial insecticides are usually effective but can have limited distribution. Misuse of synthetics through adulteration by unscrupulous traders is common, as are dangerous application rates due to illiteracy, poor labeling, or use of old, expired products, all of which contribute to the evolution of pesticide resistance. Health and safety are also serious issues since smallholder farmers typically apply with no protective clothing. Consumers, meanwhile, may be exposed to high residues. The environmental impact of synthetics on crop pollinators, natural enemies, soil systems, and food chains can be extremely problematic.

Pesticides derived from plants are well known by farmers and are more environmentally benign, safer, and cost-effective compared to synthetic pesticides as well as being more difficult to adulterate, particularly when produced or harvested by farmers themselves. Most persuasive of all is that their cost to farmers is substantially lower than synthetic products and can be calculated in terms of time to harvest and process rather than outgoings. Although generations of farmers have used plants for pest control, their priority in agricultural policy is low because there are few commercial incentives or revenues driving policy and uptake as is the case with commercial synthetic pesticides. Hundreds of NGOs, farmer associations, and research institutes have been investigating the use of botanical pesticides. However, one criticism of some of this work is that it is often not scientifically validated, and promotion is based more on anecdote than evidence.

Previous McKnight funding has provided convincing data on the efficacy and relative safety of pesticidal plants to farmers and consumers, the economic cost/benefits of their use, their lower impacts on pollinators and natural enemies, and benefits to crop yields by acting as foliar fertilizers and reducing diseases such as powdery mildew. Farmer research networks supported by McKnight in Malawi and Tanzania have been enthusiastic in the adoption of botanical pesticides, with many new farmers wanting to join and increasing their ecological knowledge, e.g. “Not all insects are bad.” As many of the farmers involved are now growing their own Tephrosia vogelii plants for use as pesticides, they observe that the soil is improving where T. vogelii is growing, enabling them to consider growing such crops as coffee, which they would not have previously considered because of poor soils. As more farmers scale up production of T. vogelii they are building nurseries and drying sheds and using centralized grinding machines. Farmers are also observing new business opportunities as they increase botanical production by providing spraying services to other farmers.

Despite these advances, many challenges remain, including closing knowledge gaps whilst building local capacity with farmers and researchers.

Grant Aims:

  • Next steps in the development of pesticidal plants (PP) should have FRNs as their research core. As farmers in these FRNs observe the positive effects of PPs on a range of pests and increased crop yield, FRNs in Malawi and Tanzania are growing through word of mouth, with many farmers wanting to join. Developing and extending the network will help facilitate nascent ideas of knowledge sharing and commercialization already developing with some farmers.
  • Expanding FRN research activities will enable problems that are repeatedly identified by farmers to be tackled, including fall armyworm on cereal crops and plant pathogens such as powdery mildew and black spot.
  • Based on a recent review of the benefits of field margin plants in enhancing ecosystem services, the project team will investigate relationships at different trophic levels, such as soil pathogens, nematodes, and insects, and how PPs facilitate crop protection through above- and below- ground interactions between pests and predators and increased crop resilience.

Outputs and Outcomes:

The overall goal of the project is to improve food security in Malawi and Tanzania through the development and optimization of plant-based pest management technologies that are simple, effective, reliable, safe, low-cost, and appropriate for the control of field and storage insect pests of legumes and cereal crops.

The research’s four main objectives are:

  • Pest management on cereal crops, including FAW
  • Plant pathogens management, including powdery mildew and black spot
  • Impacts of PPs on soil pathogens, nematodes, and below-ground invertebrates
  • Influence of PPs on crop protection through above- and below-ground interactions between pests and predators, and increased crop resilience