Aug. 26, 2019
By Ji Jing, Technical Service & Development, Industrial Solutions Asia Pacific, Dow Inc.
Flowable concentrate for seed treatment (FSC) is a pesticide formulation with film-forming property for seed treatment. FSC is made from pesticide active ingredient, film forming agent, wetting agent, dispersant and other additives. It can be directly used or diluted, and cover on the seed surface to form a “coat” with a certain strength and permeability. The “coat” can bind the pesticide active ingredients and prevent falling off, absorb water in the soil to expand without being dissolved, allow water and air to pass through for seeds germination, and ensure the contained pesticides and fertilizer to release slowly. Therefore, FSC has the effect of killing underground pests, improving seed germination rate and promoting healthy growth of seedlings.
Figure 1. Appearance of the coated seeds with the FSC containing POWERBLOX™ Filmer -17 Film Forming Agent
Film forming agent is an important component in FSC. At present, commonly used film forming agent in the market include polyvinyl alcohol (PVA), methyl cellulose, poly acrylates and other polymers with bonding and film forming properties. However, the polymers with higher bonding properties usually have lower film strength, poorer seed flow ability, less uniform appearance. Conversely, the polymers with higher film strength usually have lower adhesion strength, and easier to fall off from the seed surface; the hydrophilic polymers are easy to be dissolved in water, and the hydrophobic polymers often have negative influence on seed germination. This causes some of the current FSC products in the market still have some performance defects, such as high expulsion rate, poor water resistance and so on. In response, Dow developed a safe polymer dispersion for FSC, POWERBLOX™ Filmer-17 Film Forming Agent.
The most highlighted physical property of POWERBLOX™ Filmer-17 Film Forming Agent is its outstanding low temperature stability. After 3 cycles of freeze-thaw under -10⁰C (18 hours) and room temperature (6 hours), the appearance of POWERBLOX™ Filmer-17 is still good and maintains good flow ability.
POWERBLOX™ Filmer-17 Film Forming Agent was added into a 30% thiamethoxam FSC formulation with 10%wt. concentration, and then coated corn seeds. The appearance of the coated seeds, expulsion rate, water resistance and seed germination were tested.
Figure 2. Expulsion rate test method
The appearance of the seeds after coating is shown in Figure 1. It can be seen that POWERBLOX™ Filmer -17 Film Forming Agent provided a film on the seeds with uniform appearance and extensive coating coverage.
Expulsion rate is one of the important performance of FSC. Two different methods were used to destroy the seeds’ coat. One was shaking method, and the other was dropping method. Then measured expulsion rate respectively. A new measurement method was established to improve the repeatability and stability of the expulsion rate results. As shown in Figure 2, after the coat being destroyed, the seeds in the container were moved to another glass vial. Solvents were added into the vial to fully dissolve the active ingredient (AI) on the seed surface. In addition, solvents were added into the container to clean it completely, so that the active ingredients which remained in the container can be fully dissolved. Finally, high performance liquid chromatograph (HPLC) was used to determine the weight of active ingredient in two solutions, and expulsion rate was calculated. The expulsion rate of the coated seeds which destroyed by the shaking and dropping methods was 2.7%wt. and 5.5%wt. respectively, which can meet the relevant standard requirements.
Water resistance is required for seeds’ coating, especially for the seeds in paddy field, such as rice seeds. Good water resistance of coat avoids the loss of active ingredients during seed immersion and crop growth process. The result of water resistance is shown in Figure 3. After immersing in water, the darker the color of the water, the worse the water resistance of the coat. The results showed that POWERBLOX™ Filmer-17 Film Forming Agent provided excellent water resistance. This is because of its balanced hydrophilic-hydrophobic property. However, cellulose and PVA were strong hydrophilic, resulting in the film dissolved in water and the loss of active ingredient.
Figure 3. Water resistance of the seed coating with different film forming agents
Safety is the most important requirement for FSC. The basic requirement for safety is comparing with the seeds without coating, no negative influence on germination rate and seedling height. The result of germination experiment is shown in Table 1. It can be seen that seed germination rate (4 days) and seeding height (10 days) of the seeds with FSC contained POWERBLOX™ Filmer-17 Film Forming Agent was equivalent with the uncoated seeds, indicating that POWERBLOX™ Filmer-17 had no negative influence on seed germination, and was safe for seeds. POWERBLOX™ Filmer-17 is a dispersion with balanced hydrophobic-hydrophilic polymer, which not only provide good water resistance, but also ensure that in the seed germination process, water can be absorbed through the coat, and doesn’t influence seeds germination and the growth of seedlings.
POWERBLOX™ Filmer-17 Film Forming Agent is a polymer dispersion with outstanding low temperature stability. The 30% thiamethoxam FSC formulation containing POWERBLOX™ Filmer-17 was used to coat the corn seeds, the results showed that it can provide a film on the seeds with uniform appearance and extensive coating coverage. The expulsion rate was low, and water resistance was excellent. The germination result showed that POWERBLOX™ Filmer-17 had no negative influence on seed germination. POWERBLOX™ Filmer-17 is a safe, high-performance film forming agent that can be used in high-quality FSC formulation.
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