In today’s world, where the philosophy of green agriculture has taken deep root, the concept of “integrated fertilizer-pesticide application” has emerged as a crucial technical pathway for achieving reduced pesticide use while enhancing agricultural efficiency. Certain substances naturally possess a dual identity: they not only provide crops with essential nutrients but also effectively eliminate or suppress pests. The following section provides a detailed exposition of several representative categories of such substances, covering their fertilizer functions, insecticidal efficacy, mechanisms of action, and key application guidelines.
Azadirachtin—A Paradigm of Plant-Derived Bio-Fertilizers/Pesticides
Azadirachtin is a triterpenoid compound extracted from the seeds of the neem tree (Azadirachta indica). It stands as one of the most extensively researched and widely applied plant-derived biopesticides currently available. The Food and Agriculture Organization of the United Nations (FAO) has recommended it globally as an outstanding, eco-friendly, plant-derived pesticide.
1.Fertilizer Functions
The residue remaining after neem seeds have been pressed for oil—known as neem cake—serves as a high-quality organic fertilizer. Rich in nitrogen, phosphorus, and potassium, and abundant in organic matter, it effectively improves soil structure and enhances the soil’s capacity for nutrient and water retention.
2. Insecticidal Efficacy
Azadirachtin possesses a unique mechanism of action: its chemical structure closely resembles that of endogenous insect molting hormones (ecdysteroids). It primarily disrupts the insect’s endocrine system by reducing the release of molting hormones, thereby interfering with the insect’s normal molting and metamorphic development. Its modes of action include:
- Insect Growth Regulation: It kills insects during their larval or nymphal stages by disrupting the normal molting process.
- Antifeedant Effect: It causes pests to cease feeding, leading to gradual starvation and death.
- Repellent Effect: It acts as a repellent against a wide variety of pests.
- Systemic Action: It can be absorbed through the plant’s roots and translocated throughout the vascular system, enabling the control of pests that are difficult to eliminate via direct contact application.
3. Scope of Control
Azadirachtin demonstrates efficacy against over 300 species of harmful organisms, including aphids, thrips, leafhoppers, leaf miners, beetles, mealybugs, weevils, lepidopteran larvae, mites, and nematodes. Research indicates that the root application of granular azadirachtin formulations yields excellent control results against the beet armyworm (Spodoptera exigua), the Asian corn borer (Ostrinia furnacalis), and the cotton aphid (Aphis gossypii).
4.Key Points for Application
Azadirachtin is sensitive to ultraviolet light; therefore, direct exposure to strong sunlight should be avoided during application. It is best applied on overcast days or in the late evening. As its mode of action is relatively slow, it should be used preventively during the early stages of pest infestation.
Bacillus thuringiensis—A Breakthrough in Integrated Biopesticide-Fertilizers
Bacillus thuringiensis (Bt) is currently the most successfully applied microbial insecticide, having achieved significant breakthroughs in recent years within the field of integrated biopesticide-fertilizers.
1.Fertilizer Functionality
Recent studies indicate that by optimizing the “biofilm” formation process, the functions of Bt biopesticides can be effectively coupled with those of organic fertilizers. With the addition of fertilizer components such as humic acid, Bt formulations not only provide long-lasting pest control but also supply crops with biological nitrogen fertilizer through in situ nitrogen fixation. Field trials demonstrate that this technology has been cumulatively deployed across 120,000 mu (approx. 8,000 hectares), covering major tea and vegetable production regions throughout the country.
2. Insecticidal Efficacy
The insecticidal crystal proteins produced by Bt exhibit highly selective toxicity against specific pests, primarily targeting lepidopteran pests such as the diamondback moth and the cabbage worm. Research has revealed that certain fertilizer components can significantly enhance Bt’s insecticidal potency; specifically, a compound fertilizer (containing KCl, ZnSO₄·7H₂O, and humic acid) was found to reduce the LC50 value of a Bt wettable powder formulation to 0.139 g/L, thereby boosting its insecticidal efficacy by 3.12-fold.
3.Synergistic Mechanism
The fertilizer facilitates the formation of a more stable biofilm structure by Bt, thereby significantly enhancing its resistance to UV-induced damage and extending its effective persistence in the field.
Integrated Systems of Entomopathogenic Fungi and Organic Fertilizers
Entomopathogenic fungi—such as Beauveria bassiana, Metarhizium anisopliae, and Purpureocillium lilacinum—can be formulated in combination with organic fertilizers to create bio-fertilizers that possess insecticidal properties.
1.Fertilizer Functionality
Utilizing organic fertilizer as a carrier medium (comprising over 80% of the formulation) and incorporating organic materials such as oil cakes, these products supply crops with the essential organic matter and nutrients they require.
2.Insecticidal Efficacy
The relative virulence of these three entomopathogenic fungi against aphids follows the order: Beauveria bassiana > Purpureocillium lilacinum > Metarhizium anisopliae. A combined formulation of Beauveria bassiana and Purpureocillium lilacinum demonstrates significant synergistic effects against aphids and root-knot nematodes, achieving synergistic toxicity indices of 3.66 and 4.77, respectively. The optimal formulation consists of: “80.5% Organic Fertilizer + 14.3% Oil Cake + 8.4% Beauveria bassiana–Purpureocillium lilacinum Microbial Inoculant.”
Compound Microbial Fertilizers
Compound microbial inoculants—comprising Bacillus subtilis, Paenibacillus mucilaginosus, Bacillus licheniformis, and Acremonium spp., among others—serve a dual function: providing both pest and disease control as well as plant growth promotion.Microorganisms such as Bacillus subtilis not only inhibit pathogenic bacteria but also facilitate the degradation of pesticide residues in the soil.
Summary and Recommendations
The aforementioned substances embody the “green” philosophy of “pesticides and fertilizers from a common source.” In practical application, the following recommendations are offered: prioritize prevention by applying treatments during the initial stages of pest infestation; when using plant-derived products such as azadirachtin, avoid application during periods of intense sunlight; for microbial products, strictly avoid mixing them with chemical fungicides; and finally, integrate these dual-action pesticide-fertilizer products into comprehensive pest management systems, utilizing them in conjunction with other agronomic measures to achieve the ultimate goal of reducing chemical inputs while enhancing overall efficacy.