Producing biopesticides based on neem leaves and seeds

Arbre de neem

Biopesticides are solutions prepared from the active substances of certain plants and natural products such as ash. Here, we will focus on biopesticides based on neem, also known as margosa (Azadirachta indica), but it is possible to make them with many different plants (e.g., chili pepper, papaya leaf, etc.). Biopesticides are used when insects, caterpillars, and pests attack leaves, flowers, or pods. They are used to limit the use of chemical inputs due to their much more harmful effects on the environment and humans and because of their purchase cost.

Ecological scope and interests

The leaves and seeds of neem possess compounds such as azadirachtin, which is the main one, but there are also: melantriol, nimbine, nimbidine, nimbinine, salannine, azadirone, azadiradione, gedunine, valassinine, which are active against almost all orders of insects ^[1]. They have demonstrated their effectiveness in controlling over 400 species of arthropods, harmful nematodes, and various plant diseases. The remarkable insecticidal properties of azadirachtin, active at doses lower than 0.1 ppm, position it as one of the most promising among natural active substances extracted from plants.

At least twelve modes of action of azadirachtin have been identified; depending on the insects, it can act as a repellent, anti-feedant, or feeding deterrent, as well as a growth regulator that can affect egg-laying in females as well as the molting and growth of larvae in certain arthropods, ovicidal, larvicidal, weakening insects, and inhibiting their resistance ^[1]. Neem-based preparations can therefore replace synthetic insecticides to effectively and inexpensively combat insects and the diseases they may transmit. Moreover, neem-based products are reportedly only minimally harmful to other animals and humans^[1].

Nevertheless, a pest that causes significant damage to crops often reflects a much deeper problem of imbalance in the system. For example, its natural enemies have been eliminated, or it attacks a specific crop that represents too large a proportion of the diversity of cultivated plants.

Due to its multiple modes of action and the synergies between its different active principles, the development of resistance to neem-based biopesticides is highly unlikely^[2].

Limitations

The use of neem-based biopesticides, notably neem oil, presents limitations:

It also affects neuropterans, non-phytophagous and non-harmful insects used as beneficial organisms in crop protection.
Its use in the field is limited by its instability, primarily due to a high rate of photodegradation, its low persistence, and its slower action compared to conventional pesticides.

Susceptible Insects

Azadirachtin has been particularly effective against the following insects:

Rice weevil (Sitophilus oryzae).
Maize weevil (Sitophilus zeamais).
Lesser grain borer (Rhizopertha dominica).
Khapra beetle (Trogoderma granarium).
Cowpea weevil (Callosobruchus maculatus).
Chinese bruchid (Callosobrochus chinensis).
Mexican bean beetle (Epilachna varivestis).
Brown planthopper (Nilaparvata lugens).
Tobacco cutworm (Spodoptera litura).
Spider mites (Tetranychus spp).
Onion thrips (Thrips tabaci).
Melon fly (Dacus cucurbitae).
Mango fly (Ceratitis cosyra).
Mediterranean fruit fly (Ceratitis capitata).
Diamondback moth (Plutella xylostella).
Rice stem borer (Sesamia inferens).
Natal fruit fly (Ceratitis rosa).
Rice stem borer (Chilo suppressalis).
Cotton bollworm (Heliothis armigera).
Aphids.

Implementation conditions

Necessary equipment

Basins and buckets: Water transport and product preparation.
Machete: Cutting of plants (neem leaves).
Mortar and pestle: Grinding of leaves.
Sieve: Filtering of waste.
Jerry can: Product storage.
Sprayer or broom: Product application.
Scale: Measurement of quantities.

Materials/raw materials

Local soap made from ash.
Water.
Neem leaves.
Neem seeds.

Challenges and constraints

Sometimes it's difficult to adhere to dosages due to lack of a scale.
Producing biopesticides in sufficient quantities can be challenging.
Transportation of the product to the field is also a problem.

Preparation steps

Using leaves

Collect 10 kg of neem leaves, remove the veins, and crush.

Soak the crushed leaves in 10 liters of water for 12 hours in a first basin, then filter (the water has turned green).

Find and crush 200g of local soap. The soap acts as a binder that helps to better fix the product on the plants.

Mix the soap in 20 liters of water, wait for 12 hours, then filter.

Mix the contents of the two basins to obtain 30 liters of biopesticide.

Using seeds

Find ripe neem fruits and remove the bark and pulp by gently crushing the fruits (the bark and pulp can be used in the compost).
Dry the seeds in the shade, as the active ingredients in the seeds could be sensitive to sunlight.
Gently crush the seeds to obtain a powder. The smell of the seeds is strong, so it is advisable to use an old mortar or a mortar dedicated solely to this purpose.
Pour 10 liters of water into another basin and add 500 g of powder (~ 6 large handfuls).
Let it soak for 12 hours, then filter.
Mix with soapy water as for the maceration with the leaves.

Application mode

The mixture is sprayed at a rate of 2-3 liters per 10 m² plot on plants. To prevent its insecticidal effect from fading, spraying should be repeated approximately every 7 days. It is important to ensure that the spraying covers all parts of the plant, especially the underside of the leaves, which can sometimes be overlooked.

Stop spraying approximately 7-10 days before harvest to avoid bitterness of the biopesticide on the crops. If necessary, the biopesticide can also be used to protect crops by impregnating storage bags with the product. The effect could last several months.^[3].