Pesticides are widely used in agriculture to control pests, but their conventional formulations often suffer from low efficiency and environmental pollution. According to the release characteristics of active ingredients, sustained-release pesticide formulations can be categorized into two main types: free-release conventional and controlled-release dosage forms. Studies show that only 20% to 30% of conventional pesticides are effectively utilized, while up to 50% to 60% are lost through various pathways. This not only leads to economic waste but also causes significant environmental damage. Therefore, controlling the release amount, timing, and spatial distribution has become a key focus in the development of new pesticide formulations.
The core of controlled-release technology involves the interaction between polymer compounds and the active ingredient of the pesticide. This allows for a continuous and gradual release of the pesticide according to a preset concentration and time, maintaining an effective level over an extended period. As a result, the sustained-release formulation helps stabilize the performance of the pesticide by protecting it from environmental factors like water and air. Additionally, this technology extends the duration of the pesticide’s effect, reducing the frequency of application and the overall amount used, which significantly lowers the risk of residue and environmental contamination. It also helps reduce the toxicity and phytotoxicity of the pesticide, making it safer for both crops and the surrounding ecosystem.
Currently, sustained-release pesticide agents are divided into physical and chemical types. Physical agents involve dissolving or mixing the active ingredient with a polymer through physical methods, such as microcapsules, inclusion complexes, multilayer structures, hollow fibers, adsorbents, foams, solid solutions, dispersions, and composites. Chemical agents, on the other hand, involve forming chemical bonds between the active ingredient and the polymer, including self-polycondensates, direct bonding, and bridging combinations. Most commercially available products are physical types, with microcapsules being the most common. Among different pesticide categories, insecticides have the most sustained-release formulations, followed by herbicides and fungicides, while plant growth regulators have the fewest.
Since the introduction of microencapsulated methyl parathion by Pennwalt in the U.S. in 1974, sustained-release technology has gained considerable attention in the pesticide industry. Over 20 products have been developed, though their production volume remains limited. China also once produced microcapsules of methyl parathion and phoxim, but due to various reasons, these were not widely promoted. Overall, the development of sustained-release agents has been slow, mainly due to high material and production costs, which limit their competitiveness in the market.
In terms of research and application, the selection of sustained-release materials is crucial. To address the high cost of existing options, the Beijing Agricultural Technology Extension Station conducted studies using low-cost natural polymers, inspired by successful research on seed germination control. Through specialized processing techniques and equipment, they developed a range of sustained-release materials, including uniform and non-uniform "S" curve release types. The former ensures consistent release concentration over time, while the latter features a rising and then declining release rate, mimicking an "S" curve. Adding biodegradable polymers allows for better control of the release dynamics, aligning them with crop needs. These materials are made into pellets and coated with a polymer film, enabling slow and controlled release through the degradation of the film.
In practical applications, slow-release formulations have shown great potential in managing vegetable pests and diseases. For example, systemic insecticides like imidacloprid and aktai are combined with slow-release materials to create root-pesticide sub-pellets or granules. When crops are planted, the active ingredients are gradually released, traveling upward with transpiration to reach the leaves and control pests. This method is particularly effective during the early stages when pest populations are low, allowing for lower doses to achieve effective control. Field trials on radish amaranth showed that root pellets had some impact on emergence, while sustained-release granules had no effect on seedling emergence. In tests with Aktai, sustained-release granules applied at 675 g/ha achieved control rates of 90.9%, 100%, and 80% after 45, 55, and 80 days, compared to only 55.3%, 23%, and 0% for conventional formulations. This demonstrates a clear improvement in both efficacy and duration.
Additionally, slow-release Aktai was used to control tomato whiteflies, achieving control rates of 75%, 80%, and 70% after 30, 44, and 58 days, respectively. This approach reduced the need for repeated manual applications and improved pest management. Overall, one-time concealed application of slow-release pesticides can effectively protect vegetables throughout their growth cycle from pests like whiteflies and aphids.
Another important application is in cotton cultivation, where defoliation is used to shape the plant, control its height, and promote early maturity. This technique plays a vital role in increasing yield, especially in regions like Xinjiang, China. However, traditional defoliation methods rely on foliar application, which may not always be efficient or environmentally friendly.
This article was published by the **China Pesticide Network**. Please cite the source!
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