Author Login

Correspondence to Author: Ray Boucher, 

Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis,IN 46268, USA.

Abstract:

In a harsh environment, encapsulation can slow the breakdown of insecticides. To balance the amounts of pesticide that are degraded and absorbed by plants, however, the proper release profile design is essential. Compound A, an insecticide that degrades quickly in soil, is used in this research as an example to show how mathematical modelling in conjunction with a greenhouse study can be used to recommend an ideal release profile and aid in the creation of controlled-release formulations for active ingredients (AI). In order to determine the least dosage needed to achieve the 1-month insect control aim, a mathematical model was first built. To validate the model, a spiking greenhouse test with the specified use rate was created. Combining these data allowed researchers to arrive at the conclusion that 0.03 to 0.045 g AI/g soil was the minimal dosage for 1-month insect control in microbiologically active soil. The spike test showed that if Compound A were to be released under controlled conditions using the right encapsulation technology, it would effectively control insects for a full month while using at least nine times less of them than if it were to be released naturally. This knowledge can be used as a guide for deciding on the polymeric encapsulant’s composition, enhancing the transition from lab screening to greenhouse testing, and then enhancing the transition to field performance.

Keywords:Soil pesticide; controlled-release; modelling; degradation; pest control

Introduction: Chemicals known as pesticides are deliberately put into the environment to control undesirable pests such as weeds, fungus, and insects. Many pesticides can be created without the need of a formulation mechanism because they are inherently stable. Encapsulation technologies are frequently employed to prevent unintended effects of the environment on the pesticide in some situations when the pesticide’s physical and chemical qualities cause instability, poor mobility, and unwanted loss in storage or use. Interfacial microencapsulation, for instance, reduced the volatility of clomazone to 50% [1]. Tefluthrin’s soil mobility was improved, which resulted in improved bio-efficacy against pests that are carried by the soil [2]. Encapsulation can be employed in different situations to lessen the exposure risk [3,4].When compared to, microencapsulated lambda-cyhalothrin demonstrated significantly less eye and skin discomfort. When compared to an emulsion in water, lambda-cyhalothrin microencapsulated significantly reduced eye and skin irritation [5]. The pesticide formulations can be selectively effective against some undesired insects while remaining harmless to helpful insects or insects that do not feed on the capsule components [4] by including a base trigger within the polymeric shell.Cadusafos microcapsules have been shown to lessen mammalian toxicity while maintaining efficacy [6]. In order to prevent or delay chemical deterioration caused by incompatible substances, actives can also be encapsulated [3]. Encapsulation is anticipated to prevent or eliminate deterioration caused by pH [3], temperature, UV radiation, or microbial bio-degradation. Most of the time, this protection is obtained through the controlled release of the active, which provides pest control for the specified amount of time. Pesticides used in soil are subject to a variety of intricate processes, such as soil binding, chemical and microbiological breakdown or conjugation, and leakage into ground water. Before it can reach the insects and regulate them, the fraction that is absorbed by the plant may be subjected to plant metabolism. Before the applied pesticide gets to the insects, these steps may have an impact on its activity. Compound A is a systemic insecticide that has a short half-life due to the soil bacteria’ fast digestion of it (see Results and Discussion). In order to achieve long-term pest control, active ingredient (AI) must be fed continuously.Encapsulation technology was thought to be able to regulate Compound A’s release, providing the ideal mix of decomposition, absorption, metabolism, and insect control. To determine the minimal dosage needed to maintain pest control for one month, we first created a mathematical model. Greenhouse experiments were then employed to validate the model. The selection of the encapsulant was thenguided by the creation of an appropriate release profile. This knowledge will help in choosing the polymeric encapsulant’s composition, enhancing the transition from lab testing to greenhouse testing, and ultimately enhancing the transition to field performance.

Resources and Procedures:The Solver add-in function for Microsoft Excel was used to create the model. Test of soil deteriorationA KitchenAid K5SSWH Heavy Duty Series 5-Quart Stand Mixer was used to stir 300 grammes of Brookston silt clay loam (Hancock County, Indiana) soil. Compound A suspension was added along with water. To produce a final concentration of 8 g of Compound A per g of soil and 26 wt% water, the mixture was well blended. By combining a 15-g sample of soil with 10 mL of acetonitrile for 1 hour, the persistence of parent material (Compound A) was examined throughout a variety of time periods. After 10 minutes of centrifuging the mixture at 3500 rpm, the supernatant was filtered through a 0.2 m PTFE syringe filter. The concentration of Compound A was determined by HPLC analysis of the filtrate.

Water content of soil:A soil sample was created by combining water and five 3 mm stainless steel beads with soil. The slurry was then thoroughly homogenised after 2 minutes of low speed mixing on a reciprocal shaker. A fine tip pipette was used to collect the supernatant after the soil sample had been centrifuged at 1500 rpm for 10 minutes. Until there was no longer any supernatant, the procedure was repeated. The residual soil was weighed and then placed in a moisture determination balance, model MB45, by OHAUS. The sample was heated to 110°C for 90 s or until there was a weight change of 1 mg. The soil capacity was determined by the weight loss, which was also the soil moisture content.

Greenhouse test to establish Compound A’s minimum concentration required:By placing the soil in a pan approximately 7.5 cm deep and then heating it in an autoclave for 60 minutes at 100°C, the soil was disinfected. In order to assure full sterilisation, this procedure was repeated on the same soil on successive days. Sterile methods were used to transfer sterile soils to cups in a laminar flow hood. A 1 oz cup containing 30 grammes of sterilised soil was used for the bioassay, and 1 ml of the experimental solution was pipetted into the cup. Test solutions for Compound A were created by combining 2 ml of acetone with 2 mg of the active ingredient, followed by 198 ml of clean water. By serially diluting with clean water, lower dosages were created.Following treatment, the soil was manually blended and evenly watered to a field capacityapproximating water volume. The concentrations that were evaluated were 0.2137, 0.0267, 0.0033, and 0.0004 g of AI/g of soil. Each cup cap had a pin hole drilled into it to allow air to flow through. The cups were incubated for 14 days at 25°C in a growth environment, after which the lids were taken off and a single, 1-2 leaf cabbage was planted.In each cup, a plant (Brassica oleracea capitata) was transplanted. About 20 to 30 mixed stage green peach aphids (GPA, Myzus persicae) attacked each plant. For three days, these plants were kept in a growth chamber (16:8 L:D, 25°C) and were given distilled water irrigations as needed. After this time, the plants’ aerial parts were removed, and each plant’s overall live GPA population was counted. The average number of aphids left in the Compound A-free treatment was utilised to convert the number of surviving aphids into a percent control.For each rate, at least 4 replicate cups were used. Minitab was used to examine the data.

Test for greenhouse spiking:By dilution Compound A to a predetermined weight of deionized water, all treatment solutions were created. The Results and Discussion defined the concentration. Each 1 ounce cup had about 30 grammes of dirt, and each treatment had 4 replicates. For the spike treatments, 1 ml of the solution was added every Monday and every Thursday for 4 weeks (8 times in total). Lids were placed on the cups, and a teeny hole was drilled in the lid to let airflow. In order to keep light out, trays filled with cups were placed in an environment room that was adjusted to 25°C. On days 7, 14, or 28, cabbage seedlings were transplanted. Plants were added, and cups were watered as necessary. Each plant received a 20–30 GPA infection before being assessed three days later. By cutting the plant at the base and measuring the number of aphids on each copy, plants were rated three days after treatment (DAT). The percentage of GPA control was calculated by dividing the number of alive aphids by the total number of aphids in a control treatment without Compound A.There were additional control tests using single doses.The other setups were identical. A day 0 treatment was added for the second spiking test, and the spiking dosage was applied seven times.

Conclusion:To obtain effective pest control, caution must be given when using soil-applied pesticides because they can go through complex breakdown and absorption processes. Compound A’s fast breakdown by soil bacteria raised the bar for its residual management. To improve our comprehension of the viability of controlled-releasing Compound A to give enough insect control over the stipulated time period, a mathematical model was created. Based on experimental data and wellknown agricultural practises, a number of assumptions were made. The lowest amount of compound A required in active soil for 1-month insect control was found to be between 0.03 and 0.045 g of compound A per gramme of soil, according to theoretical estimates and greenhouse tests. This loading was greater than the 0.003-0.027 g AI/g necessary for sterile soil. In order to ascertain whether the suggested use rate would be commercially viable for soil application, a field test isrequired because there is no clear association between GH use rate and field use rate. Together, the data indicate that controlled-release Compound A can effectively control insects for a month with the right encapsulation method. Comparing encapsulated Compound A formulations to formulations without encapsulation, the use rate would be reduced by at least 9 times. If irrigation occurred more frequently, the corresponding use rate in GH testing, which ranges from 75 to 113 g per cup (2.5 to 4.3 g AI/g soil), would be significantly decreased. Finding a method that can precisely control Compound A’s release in accordance with the anticipated release profile—a highly desirable zero-order constant rate of release—is challenging [10–13]. However, the knowledge gleaned from this study provided a place to start when picking the polymeric encapsulant.

Citation:

Ray Boucher. Active Diffusion in Soil: A Investigation and its Verification in Environmental Studies. Annals of Agricultural Science And Technology 2024.