Pesticidal plants: A sustainable approach to pest control in agriculture

By Elias Biwott

Pests and diseases pose significant challenges to global agriculture, threatening crop yields and food security. These threats are exacerbated by climate change, which alters pest behaviours, extends their habitats, and creates favourable conditions for outbreaks.

As the global population grows, ensuring sufficient food production becomes increasingly urgent. However, the overuse of synthetic pesticides has led to environmental degradation, pest resistance, and health concerns, further complicating sustainable agricultural practices. Addressing these interconnected challenges requires innovative solutions that balance ecological resilience, food security, and farmers’ livelihoods worldwide.

Pesticidal plants are vital in addressing the above challenges by providing an accessible, eco-friendly pest control option. Unlike synthetic pesticides, pesticidal plants are generally safer, easier to access, and can be locally sourced. However, their widespread use requires careful management to avoid overharvesting and protect biodiversity.

Understanding biopesticides
Biopesticides are substances or mixtures of substances naturally occurring and derived from plants used to prevent, destroy,kill, control or mitigate pests. Most plants produce chemicals that deter pests, often producing a mixture of compounds that repel and stop pests from feeding on them. Economic importance of pesticidal plants. Pesticidal plants offer numerous advantages, as listed below:

1. They decrease the need for synthetic pesticides.
2. They break down rapidly, leaving minimal ecological impacts.
3. They are locally sourced, making them accessible to many farmers.
4. They are safer to handle and pose fewer risks to non-target species than synthetic pesticides.
5. They are cost-effective, and some have soil-health-enhancing properties, such as Tephrosia.
6. Pesticidal plants have economic benefits, as cultivating and selling these plants can generate jobs and income for farmers,
   reduce reliance on imported pesticides, and promote organic produce markets.

Food security and farmer livelihoods Small-scale farmers, especially in low-income regions, face significant challenges with pest infestations that can lead to crop failure. Pesticidal plants can help prevent this by, increasing agricultural productivity,supporting food security, and reducing health and safety problems. Their use also reduces costs for farmers who would otherwise need to purchase synthetic pesticides, thereby improving their income and resilience.

Harvesting, processing and use of pesticidal plants

Common names of pesticidal Plants	Target Pest	Plant part used	Preparation	Uses/action
Aloe	Newcastle in chicken Insect pests	Leaf sap	Crush leaves to extract gel,dilute in water and spray on plants;Squeeze the sap into water for chicken to drink	Antibiotic repellent.Disrupts feeding
Neem	Cockroaches, weevils, aphids, termites, mites, nematodes, cutworms, armyworms, sod worms, caterpillars, beetles, scales	Seeds, leaves and bark	Extract the oil or grind the harvested leaves, seed/bark to a powder.Dilute the oil/ powder in soapy water for spraying on crops.	Strong anti-feedant, repellent. It affects insect growth, reproduction, causing deformities.Contains Azadirachtin/ Nimbin
Blackjack	Aphids, fungal and bacterial pathogens	Leaves and stem	• Dry, boil, grind or burn to form ash. This is used or mixed in solution to spray on crops	Antifungal, and antibacterial
Sodom apple	Cattle ticks red spider mites, nematodes, aphids, beetles	Ripe fruits	Whole dry, ripe fruits are crushed and extracted in water at 5% w/v for 24 h and sprayed at 5L/ animal	Surface Application.Disrupts nervous system
Hot red pepper	Thrips, ants, aphids, caterpillars and white flies	Fruit	Dry and grind fruits. Use as a powder or mix with water and soap and apply to crops	Contains Capsaicin- irritant and deterrent
Pawpaw	Aphids, caterpillars, whiteflies, nematodes	Leaves, seeds	Pound leaves mix with water and leave to stand overnight. Sieve and Spray on crops	Contains papain- repellent, inhibits growth.
Commiphora (Myrrh) (Commiphora Holtiziana)	Ticks, skin disease, ants, termites	Bark resin	The resin extracted is applied directly mixed with milk, boiled and smeared	Acts as a repellent and has strong microbial properties.
Latifolia (Cordia latifolia)	Maize weevil, Butterfly caterpillars	Leaves	Dry plant leaves placed on grains	Strong scent acts as a repellent.
Tick clover (Desmodium spp)	Stalk borer	Whole plant as ground cover	Intercropping as a “push-pull” strategy in IPM	Repels stem borers and attracts beneficial insects that prey on the pests.
Lantana	Weevil, tuber moth, Mosquito, fly, Beetles, Aphids, whiteflies and mites	Leaves, flowers	Dry the plant leaves or whole plants and soak in water, occasionally stir and spray the liquid on affected plant parts	Contains Landadene Can be used both pre- and post-harvest as repellent.
Melia (Melia volkensii)	Termites Against a broad range of insects	Fruit pulp	Dry plant leaves mixed with water	Can be used both as a pre- and post-harvest repellent
White Ginger	Cutworms, aphids, leafhoppers, spider mites, cabbage worms	Rhizomes	Rhizomes extract prepared in warm water concoction and diluted for spray.	Rhizome oil has repellent properties and is toxic to some insects.
Sacred Basil (Ocimum tenuiflorum)	Mosquito, fleas	Leaves and stems	Smashing for sprays, sweeping with twigs, planted near the house, burning.	Repellent, antifungal, and antibacterial properties
Pyrethrum	Pickleworms, aphids, caterpillars, beetles, leaf hoppers, spider mites, bugs, cabbage worms.	Flower and seeds	Dry flowers and seeds and grind them to a powder.Mix with water for sprays.	Contains pyrethrin that acts on the insect nervous system, causing paralysis and death

Tephrosia spp (Tephrosia vogeli)	Caterpillars, beetles,aphids, spider mite • and carpenter ants.Ticks, mosquito larvae	Dried leaves	Extract by mixing 20 grams of fresh leaves with 100 ml water. Soak for two hours, adding 5 ml liquid soap to the above solution away from direct sun, filter and spray.	Surface application. Use immediately for optimum effectiveness. (Very toxic to fish and other animals if inhaled)
Capsicum/ spring onions	Aphids, caterpillars, ants and beetles,	Bulbs	Grind the bulb, mix it with water and spray. Whole plants intercropped with crops	Contain Capsaicin. Acts as a repellent.
Ash	Slugs, snails, aphids, ants	Ash dust	Dust the leaves with ash dust	Its irritant alkaline nature alters the insects’ PH, and kills their appetite.
Coriander	Aphids, spider mites, whiteflies	Whole plant	Planted along the plot Acts as a repellent.	Repellent- contains Linalool and Geraniol
Garlic	Aphids, spider mites, whiteflies, nematodes	Bulbs	Warm water concoction used	Contains allicin and sulphur- acts as as a repellent.
Consoude (Sym­phytum spp)     Tithonia	Aphids     Aphids,weevils,white flies,leaf hoppers Against plant pathogenic fungi	Leaves, roots     Leaves,roots	Grind leaves, mix with water and spray       Grind leaves, mix with water and spray	Is a repellent, also causes dehydration of the insects     Aplication
Mexican marigold	Aphids, lice, fleas, ticks, ants, white flies, weevils, red spider mites, nematodes, worms, fungi   Against intestinal parasites in domestic livestock	Whole plant, leaves, stem	Planted along the plot as repellent, ground and mixed with water, dry plant placed on grains	• Added to stored beans and maize

Safety, toxicity, and application

• Even though pesticidal plants are less toxic than synthetic pesticides, safety measures like gloves, masks, and protective clothing should be used.
• If accidental contact occurs, rinse the area with clean water.
• Grains treated with pesticidal plants must be washed or winnowed before consumption.

Addressing invasive species
Utilising invasive species as pesticidal plants can help control their spread, but care must be taken not to propagate harmful species.

Challenges in adoption and scaling
Adoption is hindered by inconsistent effectiveness, unreliable raw material supply, lack of standardised methods, and regulatory demands for data on safety and efficacy. Issues include crude extract performance, environmental impact, and compliance with pesticide registration requirements.

Identification
Correct identification of the plant species, part, harvest timing, and extraction method is crucial for efficacy.

Mode of action

• Pesticidal plants act through toxicity, repellence, anti-feedancy, growth regulation, or interrupting egg-laying.
• Farmers are encouraged to experiment with different plants, concentrations, and mixtures to optimise results.

How to extract and apply pesticidal plants for field crops

• Plant materials should be shade-dried, ground, and stored properly.
• Extraction methods vary for aromatic plants, often requiring fresh materials.
• Soap is added during extraction to enhance compound solubility and adherence to leaves.
• Spraying should be done in the late afternoon or evening to prevent compound breakdown from sunlight.
• Frequent application is necessary due to the rapid degradation of compounds.

Optimisation of pesticidal plant products

• Ensure grains are well-dried and stored in pest-proof, ventilated conditions.
• Avoid overly concentrated or diluted extracts.
• Incorporate monitoring and repeated applications to enhance pest control effectiveness.

Using plant powders, concoctions or residues for field crops

• Powders can be sprinkled directly or sprayed on plants or soil to deter pests and control pathogens.
• For grain storage, powders can be mixed with grains or applied to storage bags for insect prevention.
• Double-bagging and treated storage sacks are effective for preserving grain quality.

The future of pesticidal plants in sustainable agriculture
Pesticidal plants hold the potential for organic, sustainable pest control, reducing reliance on synthetic pesticides. They can significantly contribute to resilient agricultural practices with market development,
regulatory backing, and farmer education.

Conclusion
Pesticidal plants are sustainable, affordable alternatives to synthetic pesticides, supporting organic farming and food security. Their success depends on market support, regulation, and practical training, allowing
farmers to adopt safer, locally sourced pest control methods.