ОЦЕНКА ВЛИЯНИЯ МЕСТНЫХ ДЕФОЛИАНТОВ НА ПРОЦЕСС ДЕФОЛИАЦИИ РАСТЕНИЙ ХЛОПЧАТНИКА И ЭКСПЕРИМЕНТАЛЬНАЯ ОЦЕНКА ПОКАЗАТЕЛЯ ИХ ЭФФЕКТИВНОСТИ

УДК 633.511:632.934

Abstract

This study evaluates the agrochemical efficiency and physiological effects of newly developed local defoliants, “Fandef-M” and “Fandef-a’lo”, on the medium-fiber cotton cultivar S-8290 under field conditions in Uzbekistan. Field experiments were conducted during 2018–2020 using application rates of 5.5, 6.0, and 6.5 L ha⁻¹. Defoliation efficiency, leaf abscission, and boll opening were assessed on the 6th and 12th days after treatment. The results showed that both defoliants significantly enhanced leaf abscission and boll opening compared to the control. After 12 days, leaf abscission ranged from 87.6% to 93.3% for “Fandef-M” and from 86.45% to 90.76% for “Fandef-a’lo”. Boll opening reached 87.3–91.7% and 88.52–91.54%, respectively. The treatments also exhibited a relatively mild physiological effect, as indicated by the low proportion of dry leaves. The findings indicate a clear dose-dependent increase in defoliation efficiency within the studied range. Compared to the standard defoliant, the proposed formulations demonstrated higher effectiveness and improved crop maturation, highlighting their potential for practical application under similar soil and climatic conditions.

Аннотация

В данной работе исследована агрохимическая эффективность и физиологическое воздействие новых отечественных дефолиантов «Фандеф-М» и «Фандеф-аъло» на средневолокнистом сорте хлопчатника С-8290 в условиях Узбекистана. Полевые опыты проводились в 2018–2020 гг. с применением препаратов в нормах расхода 5,5; 6,0 и 6,5 л/га. Оценка эффективности дефолиации осуществлялась по показателям опадения листьев и раскрытия коробочек на 6-е и 12-е сутки после обработки. Результаты исследований показали, что оба препарата обеспечивали значительное повышение степени опадения листьев и раскрытия коробочек по сравнению с контрольным вариантом. На 12-е сутки после обработки уровень опадения листьев при применении препарата «Фандеф-М» составил 87,6–93,3 %, а препарата «Фандеф-аъло» — 86,45–90,76 %. Степень раскрытия коробочек достигала соответственно 87,3–91,7 % и 88,52–91,54 %. При этом препараты характеризовались относительно мягким физиологическим воздействием на растения, что подтверждалось незначительной долей высохших листьев. Установлено, что повышение нормы расхода препаратов в исследованном диапазоне сопровождалось увеличением эффективности дефолиации. По сравнению со стандартным дефолиантом изучаемые препараты продемонстрировали более высокую эффективность и способствовали ускорению созревания урожая. Полученные результаты свидетельствуют о перспективности использования дефолиантов «Фандеф-М» и «Фандеф-аъло» в практике хлопководства в аналогичных почвенно-климатических условиях.

Keywords: Defoliants, agrochemical efficiency, soil-climatic conditions, calcium chlorate, stomatal conductance, antioxidants.

Ключевые слова: дефолианты, агрохимическая эффективность, почвенно-климатические условия, хлорат кальция, устьичная проводимость, антиоксиданты.

Introduction

It is well established in global practice that obtaining high-quality and high-yield agricultural products can be achieved through the rational and effective use of various chemical preparations. Moreover, scientific research is being conducted on the negative impacts of chemical preparations on the environment and human health, as well as on measures for their mitigation [1;2].

The cultivation of economically important crops, particularly cotton, and the production of cotton raw materials using various organic and inorganic defoliants in a rational manner remains a pressing issue today. In this context, special attention is given to developing low-cost and environmentally friendly products obtained through the recycling of industrial waste and natural minerals, which do not pose a threat to human health.

During agronomic practices, the defoliation process has been found to be most effective when 45–50% of bolls in medium-staple cotton varieties are open. This approach not only ensures artificial leaf shedding but also improves air circulation within cotton rows and facilitates the maturation of young bolls. Consequently, crop weight increases, the harvesting rate of cotton raw material accelerates, and the quality of cotton suitable for high-grade processing is significantly enhanced.

To address the aforementioned pressing issue, a number of scientific and literary sources were analyzed, and the methodological approaches presented in them were utilized.

The effects of calcium and magnesium chlorate based defoliants on cotton defoliation have been studied from physiological and chemical perspectives in several local and international studies. Below, the mechanisms of action of defoliants based on calcium and magnesium chlorates on plant organisms are analyzed from a chemical standpoint.

Defoliants based on calcium and magnesium chlorates exert defoliation effects on plant organisms due to the following properties:

1. Dissociation and ionic forms. Through the dissociation of calcium and magnesium chlorates in water, the following ionic species are formed:

Ca(ClO₃)₂ → Ca²⁺ + 2ClO₃⁻                                                              (1)

Mg(ClO₃)₂ → Mg²⁺ + 2ClO₃⁻                                                            (2)

These ions constitute the primary biologically active forms of the defoliants. Specifically, chlorate (ClO₃⁻) ions exert an oxidizing effect on the cell’s reducing agents, promoting their oxidation and intensifying oxidative stress within the cell:

ClO₃⁻ + 6e⁻ + 6H⁺ → Cl⁻ + 3H₂O                                                     (3)

As a result, the activity of antioxidants (ascorbate, glutathione and superoxide dismutase (SOD), which normally neutralize the oxidizing reagents formed in the plant organism and protect the cells from oxidative damage, is reduced. This leads to the oxidation and degradation of cell membranes.

In addition, the effects of Ca²⁺, Mg²⁺, and ClO₃⁻ ions on the defoliation process and their significance have been studied by several researchers. Furthermore, numerous practical studies have been conducted on the efficacy of defoliants based on calcium and magnesium chlorates [3].

2. Oxidative reactions and ROS formation. Chlorate ions (ClO₃⁻) participate in redox (oxidation-reduction) processes in plants, leading to the generation of highly reactive oxidizing species (ROS). For example:

ClO₃⁻ + 2H⁺ + 2e⁻ → ClO₂⁻ + H₂O                                                    (4)

ClO₂⁻ + H₂O₂ → OH· + ClO₃⁻ + H⁺                                                   (5)

This reaction leads to the formation of ROS, particularly hydroxyl radicals (OH·). ROS damage cell membranes, lipids, proteins, and chloroplasts, thereby increasing oxidative stress in leaf tissues and causing their degradation.

International studies have shown that the application of defoliants leads to an increase in ROS levels and lipid peroxidation, as well as disruption of the photosynthetic process [4].

3. Photosynthesis and metabolic disturbances. Chlorate ions oxidize NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate) in cotton leaves:

NADPH + H⁺ + ClO₃⁻ → NADP⁺ + ClO₂ + H₂O                                (6)

This oxidation weakens the photosynthetic processes. During this process, ROS are generated, resulting in damage to leaf tissues. Stomatal aperture (the opening of leaf stomata) and CO₂ fixation, i.e., the plant’s ability to assimilate CO₂ into organic compounds, are reduced, leading to defoliation. For example, the application of defoliants such as TDZ has been shown to cause a significant decrease in photosynthetic indices and a reduction in stomatal conductance in plants [4].

4. Abscission mechanism and hormonal changes. Oxidative stress alters intercellular hormonal signaling in plants. For example, the generation of ROS activates pectinases and other cell wall-degrading enzymes in the abscission zone (AZ) cells.

According to international sources, the application of the TDZ defoliant has been shown to increase H₂O₂ levels and induce the formation of the abscission zone [5]. In local studies, several researchers have conducted experiments on the hormonal effects of cotton defoliants and the degree of defoliation. Their results indicate that calcium chlorate and magnesium chlorate promote the formation of the abscission zone in leaf tissues [6].

Defoliation is a crucial agronomic mechanism for enhancing the efficiency of harvesting in cotton and other crops. Defoliants induce oxidative stress in leaves, leading to the accumulation of reactive oxygen species (ROS) and cellular damage. As a result, the abscission layer is activated, and leaf shedding occurs.

Chlorate-based defoliants (e.g., magnesium chlorate) are widely used; however, they have a ‘strong’ (direct and intense) effect, necessitating formulation optimization to prevent leaf scorching. Additionally, the timing of defoliant application is critical, as spraying at an inappropriate time can reduce efficacy.

To enhance the efficacy of chlorate-based defoliants, their combined application with other chemical agents (e.g., growth regulators, desiccants) has been found to be beneficial in further improving defoliation and crop quality [7].

Magnesium chlorate is widely used in Uzbek agriculture, and its technical characteristics are also documented in national encyclopedias. For example, it exists in the form of Mg(ClO₃)₂·6H₂O, is 60% soluble in water, and is used as both a defoliant and a desiccant. Its application rates and usage conditions have also been established [8].

Additionally, a chlorate–magnesium defoliant (in liquid form) has been developed in Uzbekistan, and its availability in the market is known, with an approximate Mg(ClO₃)₂ content of 36% in aqueous solution [9].

Materials and methods

The experiment was conducted using the trial-observation method, and post-defoliation assessments of cotton phenological stages and the efficacy of the applied preparations were carried out in accordance with the methodology of the ‘Research Institute of Cotton Selection, Seed Production, and Cultivation Agro-Technologies’ under the Ministry of Water Resources and Agriculture of the Republic of Uzbekistan [10–15].

During the 2018–2020 cotton harvesting seasons, field trials of industrial samples of newly recommended defoliants based on calcium–magnesium chlorates, applied together with fertilizers, were conducted on the medium-fiber cotton cultivar ‘S-8290’. These agrochemical tests were carried out in collaboration with specialists from the ‘Chilon Gavhari’ and ‘Saxovatli Haydarali Karvon’ farms in Quva district, Fergana region, and the Research Institute of Cotton Selection, Seed Production, and Agro-Technologies, at the Fergana Scientific Experimental Station.

During the experimental trials, the cotton crop conditions were as follows: in 2018, 90–110 thousand plants per hectare; in 2019, 90–95 thousand; and in 2020, 115–120 thousand. The main stalk height of the plants was 100–110 cm in 2018, 95–100 cm in 2019, and 110–120 cm in 2020.

During the vegetation period, the condition of the cotton plants was observed to be satisfactory. During the defoliation process, weather conditions, temperature, and climate were moderate. The average daily air temperatures during the defoliation period were as follows: 25–27 °C in 2018, 24–25 °C in 2019 and 25–26 °C in 2020.

Defoliation efficiency was assessed based on experiments conducted with three replicates, and measurements were taken on the 6th and 12th days following the application of the preparations [16–20].

Results and discussion

In the control crops, the total number of leaves, changes in leaf color under the influence of the applied preparations, leaf abscission rate, number of bolls, and post-treatment boll opening were determined (Tables 1–2).

Table 1. Results of the 2018 Industrial Trials of Recommended Preparations on the ‘S-8290’ Cotton Cultivar at the ‘Chilon Gavhari’ Farm, Quva District, Fergana Region

Table 1 presents the average defoliation efficiency of the preparations on cotton plants at 6 and 12 days. The results of the trials and phenological observations of the plants indicate that the ‘Fandef-M’ preparation was effective in defoliating the ‘S-8290’ cotton cultivar. At application rates of 5.5, 6.0, and 6.5 L/ha, it caused 87.60%, 91.10%, and 93.30% leaf abscission, respectively, after 12 days. Boll opening corresponded to 87.30%, 88.20%, and 91.70% depending on the application rate.

Table 2. Results of the 2018 Industrial Trials of Recommended Preparations on the ‘S-8290’ Cotton Cultivar at the ‘Saxovatli Haydarali Karvon’ Farm, Quva District, Fergana Region

According to the data in Table 2, when the ‘Fandef-M’ defoliant was applied at a rate of 6.0 L/ha, leaf abscission reached 90.39–89.50% and boll opening reached 82.12–84.70% after 12 days. In the control samples, the boll opening process was observed to accelerate significantly. At the same time, the low number of dry leaves in the plants confirms that the tested preparation exerts a ‘mild’ effect on the plant organism.

The conducted studies also yielded positive results for the ‘Fandef-a’lo’ preparation. At application rates of 6.0–6.5 L/ha, defoliation efficiency ranged from 88.97% to 96.23%, and boll opening reached 88.27%–89.75% (Table 3).

Table 3. Effects of the ‘Fandef-a’lo’ and ‘Fandef-M’ Defoliants on Leaf Abscission and Boll Opening in the ‘S-8290’ Cotton Cultivar, as Evaluated by Specialists at the Fergana Scientific Experimental Station, PSUÉAITI, Fergana Region (2018)

For study purposes, the ‘Fandef-a’lo’ defoliant was tested on the ‘S-8290’ cotton cultivar cultivated at the Fergana Scientific Experimental Station of the Research Institute of Cotton Selection, Seed Production, and Agro-Technologies (PSUEAITI), Quva District, Fergana Region. Accordingly, agrochemical field trials in 2018 were conducted at application rates of 5.5, 6.0, and 6.5 L/ha on cotton bolls that were 45–50% opened.

According to the results of the conducted trials, 12 days after defoliation, natural leaf abscission in the control cotton was 16.25%, and natural boll opening reached 75.64%. When the tested preparation, ‘Fandef-a’lo’ defoliant, was applied at rates of 5.5, 6.0, and 6.5 L/ha, leaf abscission reached 86.35%, 88.73%, and 89.15%, respectively, while boll opening reached 88.82%, 90.63%, and 90.82%, respectively. The results obtained from the trial observations are presented in the following table.

According to the table data, when the ‘Fandef-a’lo’ defoliant was applied at rates of 5.5, 6.0, and 6.5 L/ha, leaf abscission in cotton increased by 70.10%, 72.48%, and 72.90%, respectively, and boll opening increased by 13.18%, 14.99%, and 15.18% compared to the control.

Based on the trial results of the ‘Fandef-M’ defoliant, 12 days after defoliation, natural leaf abscission in the control cotton was 16.12%, and boll opening was 76.24%. Following the application of ‘Fandef-M’ at 5.5, 6.0, and 6.5 L/ha, leaf abscission under the influence of the defoliant reached 87.22%, 89.93%, and 90.21%, respectively, while boll opening reached 87.21%, 90.78%, and 90.93%, respectively. The data obtained from the trials are presented in the following table.

The results presented in the table indicate that following the application of ‘Fandef-M’ at rates of 5.5, 6.0, and 6.5 L/ha, leaf abscission in the treated cotton increased by 71.1%, 73.81% and 74.09%, respectively, while boll opening increased by 10.97%, 14.54%, and 14.69%.

Initial trials of both ‘Fandef-M’ and ‘Fandef-a’lo’ defoliants demonstrated that these preparations significantly accelerated leaf abscission and boll opening in cotton [20, 21].

The results of the trials conducted in 2019–2020 are presented in Table 4.

Table 4. Effects of the ‘Fandef-M’ Defoliant on Leaf Abscission and Boll Opening in the ‘S-8290’ Cotton Cultivar, as Evaluated by Specialists at the Fergana Scientific Experimental Station, PSUÉAITI (2019–2020)

The ‘Fandef-a’lo’ defoliant was tested in 2019–2020 on the ‘S-8290’ cotton cultivar cultivated at the Fergana Scientific Experimental Station of PSUEAITI, Quva District, Fergana Region. Agrochemical trials were conducted at application rates of 5.5, 6.0, and 6.5 L/ha on cotton bolls that were 45–50% opened.

According to the results of the trials, 12 days after defoliation, natural leaf abscission in the control was 16.60%, and natural boll opening was 76.30%. When ‘Fandef-a’lo’ was applied at 5.5, 6.0, and 6.5 L/ha, the average leaf abscission reached 86.45%, 89.50%, and 89.76%, respectively, while boll opening reached 88.52%, 90.61%, and 90.76%.

The data presented in the table indicate that for both ‘Fandef-a’lo’ and ‘Fandef-M’, application at 5.5, 6.0, and 6.5 L/ha per hectare increased leaf abscission by 69.85%, 72.90%, and 73.16%, respectively, and boll opening by an average of 12.22%, 14.31%, and 14.46% compared to the pre-application control.

Conclusions

The effectiveness and high-yield potential of the proposed new-generation, low-harm defoliants, which not only accelerate leaf abscission but also ensure high-quality yields, are evident from the results of the conducted agrochemical trials. Based on these results, it was concluded that the above-mentioned new defoliants can be further tested in large-scale agrochemical trials across various soil and climatic conditions in the country on medium-staple cotton cultivars.

References:

1. Ergashov, D. A. Synthesis of a Complex-Acting Defoliant Based on Chlorates and Physiologically Active Compounds. PhD Dissertation in Technical Sciences, Tashkent, 2017, p. 179.
2. Eshpulatova, M. B. Development of Technology for Producing Liquid Complex Fertilizers Based on Potassium and Magnesium Sulfates. PhD Dissertation in Technical Sciences, Tashkent, 2025, p. 133.
3. Ergashev D.A., Khamdamova Sh.Sh. (2021). Production of a new cotton defoliant based on calcium‑magnesium chlorate. Nat. Volatiles & Essent. Oils, 8(4), 8224–8233.
4. Jin D., Wang X., Xu Y., Gui H., Zhang H., Dong Q., Sikder R. K., Yang G., & Song M. (2020). Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum. International Journal of Molecular Sciences, 21(8), 2738. https://doi.org/10.3390/ijms21082738
5. Xie Z., Li Y., Wang Q., Chen H., & Zhang L. (2025). Advances in cotton harvesting aids: Physiological mechanisms underlying defoliation. Frontiers in Plant Science, 16, 1570251. https://doi.org/10.3389/fpls.2025.1570251
6. Wang, L., Deng, Y., Kong, F., Duan, B., Saeed, M., Xin, M., … & Song, J. (2023). Evaluating the effects of defoliant spraying time on fibre yield and quality of different cotton cultivars. The Journal of Agricultural Science, 161(2), 205–216. https://doi.org/10.1017/S0021859623000151  
7. Perumal C., Ravichandran L., Sivakumar T., & Senthil A. (2022). Use of Defoliants for Achieving Improved Productivity and Quality of Cotton: A Review. Agricultural Reviews. DOI: 10.18805/ag.R‑2372.
8. Magnesium chlorate: chemical properties and applications. Uzbek National Encyclopedia / Qomus.INFO. (in Uzbek)
9. Liquid magnesium chlorate defoliant. Technical specifications. TSh 00203855-34:2015.-14 pages. (in Russian)
10. Chen, P., Xu, W., Zhan, Y., Yang, W., Wang, J., & Lan, Y. (2022). Evaluation of cotton defoliation rate and establishment of spray prescription map using remote sensing imagery. Remote Sensing, 14(17), 4206. https://doi.org/10.3390/rs14174206 
11. Li, W., Wu, B., Hu, B., Wan, Y., Wang, J., & Jia, M. (2024). Effects of defoliation at different fertility stages on material accumulation, physiological indices and yield of cotton. Agriculture, 14(2), 258. https://doi.org/10.3390/agriculture14020258
12. Wang, L., Deng, Y., Kong, F., Duan, B., Saeed, M., Xin, M., … & Song, J. (2023). Evaluating the effects of defoliant spraying time on fibre yield and quality of different cotton cultivars. The Journal of Agricultural Science, 161(2), 205–216. https://doi.org/10.1017/S0021859623000151 
13. Neupane, J., Smith, A., Li, H., & Patel, R. (2023). Effect of controlled defoliant application on cotton fiber quality. Applied Sciences, 13(9), 5694. https://doi.org/10.3390/app13095694 
14. Zavala, R., Martínez, L., Gómez, P., & Hernández, M. (2025). Evaluation of cotton defoliation rate using remote sensing imagery. Remote Sensing, 14(17), 4206. https://doi.org/10.3390/rs14174206
15. Guo, Y., Zhang, H., Gao, W., Chen, Q., Chang, Q., Wang, J., Zeng, Q., Xu, H., & Chen, Q. (2025). Identification of Cotton Defoliation Sensitive Materials Based on UAV Multispectral Imaging. Agriculture, 15(9), 965. https://doi.org/10.3390/agriculture15090965 
16. Ergashev, D., Askarova, M., & Tukhtaev, S. (2016). Investigation of the mutual interactions of the components of a system substantiating the process of obtaining a new defoliant. Journal of Chemical Technology and Metallurgy, 51(3), 287–296. Retrieved from https://journal.uctm.edu/node/j2016-3/7-Dilmurod_Ergashev_287.pdf
17. Zhang, Z., Yu, K., Du, M., Wang, Y., Hou, H., Yang, M., … & Li, Z. (2025). Optimizing harvest aid applications for mechanical cotton harvesting: A meta‑analysis… Field Crops Research, 336, 110214. https://doi.org/10.1016/j.fcr.2025.110214 
18. Ergashev, D. A. (2020). Technology of obtaining a new complex‑acting defoliant. International Journal of Advanced Research in Science, Engineering and Technology, 7(10), 15321–15324. Retrieved from https://www.ijarset.com/upload/2020/october/45-usovoxauss-43.PDF
19. Wang, L., Deng, Y., Kong, F., Duan, B., Saeed, M., Xin, M., … & Song, J. (2023). Evaluating the effects of defoliant spraying time… The Journal of Agricultural Science, 161(2), 205–216. https://doi.org/10.1017/S0021859623000151
20. Ergashev, D. A., & Khamdamova, S. Sh. (2022). Investigation of the conversion process of calcium and magnesium chloride solution with sodium chloride. International Journal of Materials and Chemistry, 12(2), 27–31. Retrieved from https://article.sapub.org/10.5923.j.ijmc.20221202.02
21. Certificate No. B220119 issued by the Plant Protection and Quarantine Agency of the Republic of Uzbekistan regarding the registration of chemical and biological plant protection agents and mineral and microbiological fertilizers. Tashkent (registration number and date of the product: No. 10.2, 28-03-2022). (in Uzbek)
22. Ts 04643516-15:2018. Technical specifications for “Fandef-a’lo” defoliant, approved by the Uzstandard Agency Department of Standardization and State Control. (in Uzbek)