Residual activity of isoxaflutole under water restriction in contrasting soil textures of forest plantations

Residual activity of isoxaflutole under water restriction in contrasting soil textures of forest plantations | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Residual activity of isoxaflutole under water restriction in contrasting soil textures of forest plantations Fabricio Gomes de Oliveira Sebok, Edivaldo Domingues Velini, Caio Antonio Carbonari, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9586051/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Forest plantations, particularly eucalyptus, are highly sensitive to weed interference during the establishment phase, making the use of residual herbicides a common management practice. However, irregular rainfall after planting may delay herbicide activation and alter its persistence in the soil. This study evaluated the residual activity of isoxaflutole and its active metabolite diketonitrile (DKN) on the control of Urochloa decumbens and Panicum maximum in soils with contrasting textures under different post-application water restriction periods. A greenhouse experiment was conducted using sandy and clayey soils in a completely randomized design, arranged in a 2 × 5 factorial scheme, with isoxaflutole applied at 150 g a.i. ha⁻¹ and water restriction periods of 0, 30, 60, 90, and 120 days. After each restriction period, a simulated rainfall of 20 mm was applied. Weed control, shoot dry biomass, and soil concentrations of isoxaflutole + DKN were evaluated. In the absence of water restriction, complete control of both species was observed in both soil types. Increasing periods without rainfall reduced herbicide efficacy, particularly in sandy soil. Isoxaflutole + DKN persistence was consistently higher in clayey soil, resulting in sustained weed control and lower biomass accumulation even after prolonged water restriction. These results demonstrate that soil texture and post-application moisture conditions strongly influence the residual performance of isoxaflutole and should be considered when planning weed management strategies during the establishment of eucalyptus plantations under conditions of delayed or irregular rainfall. These findings provide practical support for defining herbicide strategies in eucalyptus plantations established under irregular rainfall, highlighting soil texture as a key factor determining the effective window of residual weed control. Pre-emergence herbicide weed interference soil–herbicide interaction residual activity silviculture Figures Figure 1 Figure 2 Figure 3 Introduction Forest plantations play a central role in Brazilian silviculture. In 2024, commercial forest areas in Brazil reached approximately 10.52 million hectares, representing an increase of 2.8% compared to 2023, with eucalyptus accounting for about 77% of the total planted area (IBÁ, 2025). Despite the rapid growth of eucalyptus, weed interference during the establishment phase can significantly compromise stand development and productivity. Forest plantation establishment is frequently challenged by irregular rainfall patterns immediately after planting, particularly in newly converted areas with coarse-textured soils. Under such conditions, preemergence herbicides may remain inactive for prolonged periods, increasing the risk of early weed interference once rainfall resumes. In eucalyptus plantations, this scenario is especially critical because competition during the initial growth phase can compromise stand uniformity, increase operational costs, and reduce long-term productivity. Therefore, understanding how soil texture and post application water restriction affect herbicide persistence and biological effectiveness is essential for decision-making in forest weed management programs. Among the main weed species occurring in forest systems, grasses are particularly aggressive due to their rapid growth and high competitive ability. The presence of signal grass ( Urochloa decumbens ) may reduce eucalyptus stem diameter by up to 71% and plant height by 68% (Toledo et al., 2000). Similarly, guinea grass ( Panicum maximum ) can significantly reduce growth parameters of eucalyptus plants even at low infestation levels during the early establishment phase (Dinardo et al., 2003 ). Given this scenario, integrated weed management is essential in forest plantations, with chemical control being one of the most widely adopted strategies due to its operational efficiency. The use of pre-emergence herbicides after planting allows the extension of the weed-free period because of their residual activity in the soil (Monquero et al., 2008a ). However, the persistence and effectiveness of these molecules are influenced by several factors, including soil texture, rainfall amount and timing, and climatic conditions (Carbonari et al., 2020 ; Mancuso et al., 2011 ). Among the herbicides registered for Eucalyptus cultivation, isoxaflutole stands out. It acts by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), which is essential for the synthesis of tocopherol and plastoquinone (Pallet, 1998). Inhibition of this enzyme leads to the disappearance of photosynthetic pigments, resulting in the symptom known as “bleaching,” followed by growth arrest and tissue necrosis (Pallet et al., 1998 ). The main target species of this herbicide are grasses and some broadleaf weeds (Silva and Silva, 2007 ). Isoxaflutole is classified as a pro-herbicide, as its parent molecule is not phytotoxic and herbicidal activity depends on its conversion to the active metabolite diketonitrile (DKN) (Marchiori Jr. et al., 2005 ). Compared with isoxaflutole, DKN is more soluble (326 mg L⁻¹), chemically stable, and persistent in soil, with a reported half-life exceeding 56 days at pH 7.0 and 2.5% organic carbon. In contrast, the parent compound exhibits a half-life of less than two days under similar conditions (Taylor-Lovell et al., 2000 ; Taylor-Lovell et al., 2002 ). The persistence and spatial distribution of both compounds in the soil profile are strongly governed by soil moisture regimes and vertical transport processes, as demonstrated by recent modeling studies (Gassmann et al., 2021 ). Because the activation of isoxaflutole is moisture-dependent, postapplication water restriction may delay its conversion to DKN and compromise residual weed control. Under prolonged dry conditions, the herbicide may remain largely inactive in the soil until rainfall occurs, a moment that often coincides with intense weed emergence (Oliveira Jr. et al., 2006 ). Previous studies have consistently shown that extended dry periods after application reduce isoxaflutole efficacy, particularly in soils with lighter texture (Marchiori Jr. et al., 2005 ). In forest systems, the effects of soil moisture on isoxaflutole behavior are further modulated by soil physical attributes, rainfall timing, and surface conditions during plantation establishment. Interactions between soil texture and postapplication rainfall strongly influence herbicide persistence, weed emergence dynamics, and overall control efficiency, reinforcing the importance of site-specific management strategies in forest plantations (Gassmann et al., 2021 ; Duque et al., 2023 ). Therefore, this study aimed to quantify the residual activity of isoxaflutole and its active metabolite DKN in soils with contrasting textures under prolonged postapplication water restriction, linking herbicide persistence to weed control efficiency during eucalyptus plantation establishment. Materials and methods The experiments were conducted in a greenhouse at the Núcleo de Pesquisas Avançadas em Matologia (NUPAM), Faculty of Agronomic Sciences – UNESP, Botucatu, SP, Brazil. Two soils with distinct characteristics were used. The first was a clay-textured soil collected from an area with different cropping systems at FCA/UNESP, and the second was a sandy-textured soil collected from a forestry production area in the municipality of Três Lagoas, SP. The physicochemical properties of both soils are presented in Table 1 . Table 1 Physicochemical characteristics of the soils used in the experiments. Chemical Characteristics Soil pH CaCl 2 OM g dm − 3 P resin mg dm − 3 Al 3+ K Ca Mg SB CEC V% mmolc dm − 3 Sandy 4,4 13 4 3 0,34 5 4 9 26 36 Clay 4,2 17 4 9 0,57 4 2 6 34 17 Physical Characteristics Soil Sand Silt Clay Texture g Kg − 1 Sandy 870 69 61 Sandy Clay 210 98 692 Clay The experiments were conducted in a completely randomized design (CRD) arranged in a 2 × 5 factorial scheme, with five replications. Treatments consisted of two doses of isoxaflutole (Fordor® – 750 g kg⁻¹): 0 and 150 g a.i. ha⁻¹, and five water restriction periods after herbicide application: 0, 30, 60, 90, and 120 days. This experimental design was applied to two soil types (sandy and clayey) and evaluated for the control of two grass species: signal grass ( Urochloa decumbens ) and guinea grass ( Panicum maximum ). The isoxaflutole dose of 150 g a.i. ha⁻¹ was selected because it represents a commonly adopted operational rate in forest plantation establishment. The combined quantification of isoxaflutole and DKN was used to represent the biologically active fraction in soil, as both compounds contribute to residual weed suppression under field-relevant conditions. Experimental units consisted of 2.5 L pots filled with the respective soils. Both species were sown at rates of 1.314 and 0.126 g of seed per pot, respectively, to achieve the emergence of approximately 25 seedlings of each species per experimental unit. Seeds were incorporated at a depth of 3 cm. Herbicide application was performed immediately after sowing using an automated sprayer within a closed environment. The system consisted of a 2-meter spray boom driven by an electric motor coupled with a frequency modulator, allowing control of the application speed. The boom was equipped with four XR 110.02 VS flat-fan nozzles spaced 0.5 m apart and positioned 0.5 m above the target. The working pressure was set at 2.0 kgf cm⁻², with a travel speed of 3.6 km h⁻¹ and a spray volume of 200 L ha⁻¹. At the end of each water restriction period, a simulated rainfall event of 20 mm was applied using the same automated system, adapted for rainfall simulation. Following the simulated rainfall, pots were irrigated uniformly to maintain soil moisture adequate for seed germination. To determine the efficacy and persistence of isoxaflutole, the following variables were evaluated: control percentage, shoot biomass, and soil concentrations of isoxaflutole and its metabolite DKN. Weed control was visually assessed at 15, 30, and 60 days after the simulated rainfall using a 0–100% scale, where 0 corresponds to no injury and 100% to complete plant death (Velini, 1995 ). After the final control assessment at 60 days, the shoots were collected and oven-dried at 60°C for 72 hours in a forced-air circulation system. The experimental conditions were designed to simulate post-planting scenarios commonly observed in eucalyptus plantations subjected to delayed rainfall after herbicide application, as reported in studies evaluating residual herbicides under forest conditions (Marchiori Jr. et al., 2005 ; Oliveira Jr. et al., 2006 ). Quantification of isoxaflutole and DKN in soil Soil samples for the analysis of isoxaflutole and DKN concentrations were collected seven days after the simulated rainfall for each water restriction period using cylindrical samplers 9 cm in length. Four subsamples were collected per pot, thoroughly mixed, and stored at − 20°C. Isoxaflutole and DKN were quantified together, which does not compromise the assessment of herbicide efficacy, selectivity, or environmental behavior, as DKN is an active metabolite with herbicidal activity that rapidly transforms in soil (Taylor-Lovell et al., 2000 ; Mitra et al., 2000 ; Taylor-Lovell et al., 2002 ). For compound quantification, soils were homogenized and placed in aluminum trays for drying in an oven at 40°C for 48 hours. An aliquot of 7 g from each sample was weighed and transferred to plastic cartridges containing a glass fiber filter at the bottom for solution filtration, with 3 mL collection vials attached externally to collect the extracted material. Samples were saturated with 1.5 mL and 3.0 mL of distilled water for sandy and clayey soils, respectively, and maintained under saturated conditions for 24 hours. After this period, samples were centrifuged for 5 minutes at 4000 rpm. The supernatant was then filtered through 0.2 µm Millipore filters and transferred to 2 mL vials for LC-MS/MS analysis. The LC-MS/MS system consisted of a Shimadzu Proeminence UFLC high-performance liquid chromatograph (HPLC), which allows ultrafast analysis with excellent separation performance and high reliability of results. The system was equipped with two LC-20AD pumps, an SIL-20AC autosampler, a DGU-20A5 degasser, a CBM-20A system controller (enabling fully automated operation), and a CTO-20AC column oven for temperature control. Coupled to the HPLC was a hybrid triple quadrupole 3200 Q TRAP mass spectrometer (Applied Biosystems), in which Q1 and Q3 act as mass filters, and Q2 functions as a collision cell where intact Q1 ions and fragments are further broken into smaller mass fragments. This analytical setup follows validated multiresidue protocols for the simultaneous quantification of isoxaflutole and its transformation products in complex matrices (Lan et al., 2022 ). Data analysis For data analysis, the results were subjected to analysis of variance (ANOVA) at a significance level of p ≤ 0.05, and the confidence interval (CI) was calculated using the t-test: IC = t*DP/√(n) Where t refers to the tabulated t-value (p ≤ 0.05), SD is the standard deviation of the data, and n is the number of samples. For control and biomass data, when significant, means were compared using Tukey’s test (p ≤ 0.05). For isoxaflutole + DKN concentrations, the data were fitted to a nonlinear log-logistic regression model as proposed by Streibig et al. (1980): y =a/[1+(x/b ) c ] Where y = concentration of isoxaflutole + DKN; x = water restriction period (days); a = asymptote between the maximum and minimum values of the variable; b = period corresponding to 50% of the asymptote; and c = slope of the curve. Results Higher residual concentrations of isoxaflutole + DKN were observed in clayey soil compared to sandy soil. In sandy soil, a 50% reduction in product concentration occurred after just 1 day of water restriction, whereas in clayey soil the same reduction was reached only after 4.5 days. This difference becomes even more pronounced when considering a 90% reduction of the compounds: in clayey soil, this reduction occurred only after 103 days of water restriction, while in sandy soil it was observed after just 10 days. These results explain the higher control percentages and greater biomass reduction observed for Urochloa decumbens and Panicum maximum throughout the evaluation periods (Fig. 1 ). Across all evaluated periods, the control of Urochloa decumbens and Panicum maximum was satisfactory (100%) in the absence of water restriction, regardless of soil texture. In other words, rainfall immediately following application ensured maximum control up to 60 days after the simulated rainfall (Fig. 1 ). As the duration of water restriction periods after isoxaflutole application increased, the control of these species began to vary according to soil texture (Fig. 1 ). For the control of Urochloa decumbens , no differences in control percentage were observed between clayey and sandy soils up to 30 days of water restriction. After this period, in clayey soil, control remained above 95% at all three evaluation times (15, 30, and 60 days after simulated rainfall – DAS), even with water restriction extended to 120 days. In sandy soil, however, control decreased from 60 days of water restriction onward (83–90%, depending on the evaluation time), reaching 50% at 60 DAS under 120 days of restriction (Fig. 2 ). Comparable patterns have been reported in Brazilian forestry systems, where rainfall timing and eucalyptus harvest residues modulate herbicide bioavailability and field performance (Carbonari et al., 2020 ; Duque et al., 2023 ). A similar pattern was observed for Panicum maximum , except at 15 DAS, where differences in control between the soils were recorded under 30 days of drought. At 60 days of restriction, control in sandy soil ranged from 70 to 80%, depending on the evaluation time, showing lower values than those observed for signal grass. Nevertheless, under the longest restriction period (120 days), control remained around 50%. The higher control levels of both species in clayey soil reflect the greater persistence of isoxaflutole in this texture (Fig. 2 ). Regarding shoot biomass, for U. decumbens, plant growth and development were not affected by soil texture up to 60 days of water restriction, with the lowest biomass percentages observed in both soils relative to untreated control. From 90 days onward, biomass in clayey soil remained like previous periods, showing differentiation only at 120 days. In sandy soil, biomass increased more markedly from 90 days of water restriction. For P. maximum, biomass increase occurred from 60 days of restriction in sandy soil, whereas in clayey soil this increase was significant only at 120 days (Fig. 3 ). These results, together with the concentrations of isoxaflutole + DKN in the soil (Fig. 1 ), indicate that the longer the period of drought after application, the lower the herbicide activity, as it tends to remain adsorbed to soil colloids and, in the case of isoxaflutole, is less converted into DKN. According to classical studies on residual herbicides, isoxaflutole can maintain biological activity under conditions of limited soil moisture, remaining available in the soil until rainfall promotes its activation and uptake by germinating weeds (Rodrigues and Almeida, 1998 ). This behavior helps explain the maintenance of weed control observed after intermediate periods of water restriction, particularly in clayey soil. The results demonstrate greater persistence of isoxaflutole in clayey soil (Fig. 1 ) and more effective control of the species, even after prolonged periods of water restriction in this soil type (Fig. 2 ), which is reflected in the lower shoot biomass of both grasses compared to sandy soil (Fig. 3 ). Discussion The contrasting persistence patterns observed between sandy and clayey soils have direct implications for weed management during eucalyptus establishment under irregular rainfall. In clayey soils, higher retention and slower dissipation of isoxaflutole and DKN extended the period of effective weed suppression even after prolonged water restriction. In contrast, the rapid decline in herbicide availability in sandy soils reduced residual control, increasing the likelihood of weed emergence following delayed rainfall events. These differences highlight soil texture as a key risk factor when defining herbicide-based strategies for forest plantation deployment. The lower leaching potential of isoxaflutole occurs in clayey soils, as well as in soils with higher organic carbon content. In addition to organic matter, soil pH also influences the sorption of this molecule; higher pH values are associated with lower sorption and, consequently, greater leaching potential (Mitra et al., 1999 ). Sorption of isoxaflutole also decreases with decreasing soil organic matter content (Mitra et al., 1999 ). Another factor contributing to greater herbicide persistence is related to clay characteristics, which have higher specific surface area and cation exchange capacity, enhancing retention of isoxaflutole in the soil (Melo et al., 2010 ). Based on soil analysis (Table 1 ) and the results obtained in this study (Fig. 1 ), it can be inferred that organic matter and clay content significantly influence the persistence of isoxaflutole in clayey soils. Inoue et al. ( 2007 ), when evaluating herbicide movement in sandy and clayey soils, observed differences in the behavior of this molecule, possibly associated with variations in soil organic carbon and, to a lesser extent, pH. Marchiori Jr. et al. ( 2005 ) reported greater stability and persistence of the residual effect of isoxaflutole in clayey soil compared to sandy-loam soil, attributing these differences to variations in organic carbon and clay content (10.30 × 3.07 mg dm⁻³ and 72 × 27%, for clayey and sandy soils, respectively). Marchiori Jr. et al. ( 2005 ) also demonstrated higher control of Panicum maximum compared to Urochloa decumbens at a dose of 180 g a.i. ha⁻¹, 15 days after sowing in sandy-loam soil. This difference in control between species may be explained by differences in herbicide metabolism rates. In sensitive species, the metabolic process is slower, whereas in more tolerant plants, such as eucalyptus (Adoryan et al., 2002 ), sugarcane, and maize (Oliveira Júnior et al., 2006), the transformation of DKN into benzoic acid and CO₂ occurs more rapidly. Furthermore, Marchiori Jr. et al. ( 2005 ) reported over 90% control for these species in clayey soil at doses of 230 and 270 g a.i. ha⁻¹ of isoxaflutole, even under water restriction periods of up to 120 days. In sandy-loam soils, however, control values were lower for both species across all water restriction periods, corroborating the results obtained in the present study. Biomass accumulation analysis also confirmed that control of both species over time was more effective in clayey soils. Similar results were observed by Melo et al. ( 2010 ), who evaluated shoot dry mass of sorghum (Sorghum bicolor) grown in soil columns up to 30 cm deep, subjected to surface applications of isoxaflutole (113 and 169 g a.i. ha⁻¹) followed by two 40 mm simulated rainfall events. Monquero et al. ( 2008b ) also reported albinism symptoms in sorghum plants grown in similar soil columns up to 25 cm, observing that control percentage increased proportionally with the amount of applied rainfall. From a forest management perspective, the greater persistence of isoxaflutole observed in clayey soils under prolonged water restriction has important operational implications. Previous studies conducted in eucalyptus systems have shown that soil texture, organic matter content, and rainfall timing are key drivers of herbicide behavior and weed control efficacy (Carbonari et al., 2020 ; Marchiori Jr. et al., 2005 ). Recent modelling approaches further indicate that soil moisture dynamics strongly govern the fate and vertical distribution of isoxaflutole and DKN in soil profiles, affecting the duration of effective weed suppression (Gassmann et al., 2021 ). In this context, extended herbicide persistence in clayey soils may increase the effective weed control window in eucalyptus plantations established under irregular rainfall, reducing the need for early post-emergence interventions. Conversely, the lower persistence observed in sandy soils reinforces the importance of adjusting application timing and management strategies according to site-specific soil and climatic conditions, as also highlighted in recent forestry studies (Duque et al., 2023 ). Even after prolonged post application drought, isoxaflutole maintains effective residual weed control in clayey soils, whereas sandy soils exhibit rapid loss of persistence, increasing the vulnerability of eucalyptus plantations to early weed interference under irregular rainfall conditions. In this context, the combined assessment of chemical persistence and biological response under extended dry periods advances previous studies by explicitly linking soil texture, moisture regimes, and residual herbicide performance in forest production systems. Although the experiment was conducted under greenhouse conditions, the imposed water restriction periods and rainfall simulation were designed to reproduce post-planting scenarios commonly observed in commercial eucalyptus plantations subjected to delayed or irregular rainfall, allowing consistent interpretation of herbicide behavior under operationally relevant conditions. Conclusion From an operational perspective, these findings indicate that isoxaflutole use in sandy soils under forecasted dry periods should be carefully planned, with adjustments in application timing or complementary management practices, whereas clayey soils provide a wider safety margin for residual weed control during eucalyptus establishment. Soil texture should therefore be considered a primary factor when defining the reliability of isoxaflutole residual control during eucalyptus establishment under uncertain rainfall conditions. Declarations Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Author Contribution F.G.O.S. contributed to conceptualization and overall leadership of the study.E.D.V. contributed to project administration, investigation, and provision of resources.C.A.C. contributed to resources.N.C.B. contributed to data curation, methodology, and data analysis.R.N.C. contributed to data curation, methodology, and data analysis.J.T.F.T. contributed to data curation.B.F.G. contributed to data curation.All authors reviewed and approved the final manuscript. Acknowledgement The authors acknowledge the institutional support provided by Universidade Estadual “Júlio de Mesquita Filho” (UNESP) during the development of this study. References Adoryan ML, Bendeck OB, Gelmini GA (2002) Eficácia e seletividade do herbicida isoxaflutole na cultura de Eucalyptus grandis . 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Acta Agriculturae Scand 30:59–64 Taylor-Lovell S, Sims GK, Wax LM, Hasset JJ (2000) Hydrolysis and soil adsorption of the labile herbicide isoxaflutole. Environ Sci Technol 34(19):3186–3190 Taylor-Lovell S, Sims GK, Wax LM (2002) Effects of moisture, temperature, and biological activity on the degradation of isoxaflutole in soil. J Agric Food Chem 50(20):5626–5633 Velini ED (1995) Estudos e desenvolvimento de métodos experimentais e amostrais adaptados à matologia . PhD thesis, Universidade Estadual Paulista, Jaboticabal Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9586051","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":633897185,"identity":"658f9a17-463e-4a3a-8675-53c8a820a8f1","order_by":0,"name":"Fabricio Gomes de Oliveira Sebok","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8ElEQVRIiWNgGAWjYBAC9gYeBoYEBgkQm42B4YANRJixAbcWngOoWtKI1AIFIC2HidDCfvbYhwc1FnIM/IePPfhw5nzidvb2Zw8Yd9zDrYUnL3lGwjEJYwaJtHTDGTduJ+7sOWNuwHimGKcWe4YcY4bEBgkg4jGT5vlwO3HDjRw2Cca2BNy28L+BauE//w2o5VzihvvPn+HXIgGzhSGHTZrnxgGgLQxmBLS8S2YA+YVNIs3ccMaZZOMNZ3LMDRLP4HNY7mHGHzV1cvz8h589+HDMTnbD8ePPHnzcgVsLHLChsInQgFv7KBgFo2AUjAIGAJWqVTaiUTZ0AAAAAElFTkSuQmCC","orcid":"","institution":"São Paulo State University","correspondingAuthor":true,"prefix":"","firstName":"Fabricio","middleName":"Gomes de Oliveira","lastName":"Sebok","suffix":""},{"id":633897186,"identity":"2cb78a37-7c2d-4e78-a820-b9a1b328bd12","order_by":1,"name":"Edivaldo Domingues Velini","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Edivaldo","middleName":"Domingues","lastName":"Velini","suffix":""},{"id":633897187,"identity":"f266c168-2958-4d92-967a-f9301bb50960","order_by":2,"name":"Caio Antonio Carbonari","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Caio","middleName":"Antonio","lastName":"Carbonari","suffix":""},{"id":633897188,"identity":"1b7977a5-4c64-4872-8589-f9f6960abab4","order_by":3,"name":"Natalia da Cunha Bevilaqua","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Natalia","middleName":"da Cunha","lastName":"Bevilaqua","suffix":""},{"id":633897189,"identity":"d127dd3c-7179-428d-981c-f96646dbb2f7","order_by":4,"name":"Renato Nunes Costa","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Renato","middleName":"Nunes","lastName":"Costa","suffix":""},{"id":633897190,"identity":"34c6058b-809e-4694-bd40-a38acd33930c","order_by":5,"name":"Jéssica Taynara Faria Teodoro","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Jéssica","middleName":"Taynara Faria","lastName":"Teodoro","suffix":""},{"id":633897191,"identity":"befdae86-23c4-40a8-b99c-a1e8cb24fedc","order_by":6,"name":"Bruno Flaibam Giovanelli","email":"","orcid":"","institution":"São Paulo State University","correspondingAuthor":false,"prefix":"","firstName":"Bruno","middleName":"Flaibam","lastName":"Giovanelli","suffix":""}],"badges":[],"createdAt":"2026-05-01 12:38:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9586051/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9586051/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108674473,"identity":"1bc68cf3-1b09-4485-8e3c-edc309a8b5eb","added_by":"auto","created_at":"2026-05-07 08:20:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":246479,"visible":true,"origin":"","legend":"\u003cp\u003eIsoxaflutole + DKN concentration (ng g⁻¹ soil) seven days after simulated rainfall, as affected by soil type and water restriction periods following isoxaflutole application (150 g a.i. ha⁻¹). Error bars represent the confidence interval (p ≤ 0.05).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9586051/v1/7f3c2516000a3fe0bbf92487.png"},{"id":108674474,"identity":"9a5aeee8-6cc9-4c65-a96b-0dcae21a8739","added_by":"auto","created_at":"2026-05-07 08:20:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":332031,"visible":true,"origin":"","legend":"\u003cp\u003eControl (%) of \u003cem\u003eU. decumbens\u003c/em\u003e and \u003cem\u003eP. maximum\u003c/em\u003e at 15, 30, and 60 days after simulated rainfall (DAS), as affected by soil type and water restriction periods following isoxaflutole application (150 g a.i. ha⁻¹). Means followed by the same lowercase letter within water restriction periods for each soil type, and uppercase letters between soil types for each restriction period, do not differ according to Tukey’s test (p ≤ 0.05). Error bars represent the confidence interval (p ≤ 0.05).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9586051/v1/3224a04516b9cfa0a28a6539.png"},{"id":108674475,"identity":"5855587c-8bb9-48d3-9cb1-5268dcdcb8b7","added_by":"auto","created_at":"2026-05-07 08:20:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":244528,"visible":true,"origin":"","legend":"\u003cp\u003eShoot dry mass (% relative to the control) of U. decumbens and P. maximum at 60 days after simulated rainfall (DAS), as affected by soil type and water restriction periods following isoxaflutole application (150 g a.i. ha⁻¹). Means followed by the same lowercase letter within water restriction periods for each soil type, and uppercase letters between soil types for each restriction period, do not differ according to Tukey’s test (p ≤ 0.05). Error bars represent the confidence interval (p ≤ 0.05).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9586051/v1/ef58d95c75c6534cd587a44c.png"},{"id":108806189,"identity":"3abd5ab1-8c0d-4931-b317-39b51bd2c290","added_by":"auto","created_at":"2026-05-08 15:27:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1063866,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9586051/v1/5d495116-e1b9-4f0f-978b-5c7857c586b3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Residual activity of isoxaflutole under water restriction in contrasting soil textures of forest plantations","fulltext":[{"header":"Introduction","content":"\u003cp\u003eForest plantations play a central role in Brazilian silviculture. In 2024, commercial forest areas in Brazil reached approximately 10.52\u0026nbsp;million hectares, representing an increase of 2.8% compared to 2023, with eucalyptus accounting for about 77% of the total planted area (IB\u0026Aacute;, 2025). Despite the rapid growth of eucalyptus, weed interference during the establishment phase can significantly compromise stand development and productivity.\u003c/p\u003e \u003cp\u003eForest plantation establishment is frequently challenged by irregular rainfall patterns immediately after planting, particularly in newly converted areas with coarse-textured soils. Under such conditions, preemergence herbicides may remain inactive for prolonged periods, increasing the risk of early weed interference once rainfall resumes. In eucalyptus plantations, this scenario is especially critical because competition during the initial growth phase can compromise stand uniformity, increase operational costs, and reduce long-term productivity. Therefore, understanding how soil texture and post application water restriction affect herbicide persistence and biological effectiveness is essential for decision-making in forest weed management programs.\u003c/p\u003e \u003cp\u003eAmong the main weed species occurring in forest systems, grasses are particularly aggressive due to their rapid growth and high competitive ability. The presence of signal grass (\u003cem\u003eUrochloa decumbens\u003c/em\u003e) may reduce eucalyptus stem diameter by up to 71% and plant height by 68% (Toledo et al., 2000). Similarly, guinea grass (\u003cem\u003ePanicum maximum\u003c/em\u003e) can significantly reduce growth parameters of eucalyptus plants even at low infestation levels during the early establishment phase (Dinardo et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGiven this scenario, integrated weed management is essential in forest plantations, with chemical control being one of the most widely adopted strategies due to its operational efficiency. The use of pre-emergence herbicides after planting allows the extension of the weed-free period because of their residual activity in the soil (Monquero et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008a\u003c/span\u003e). However, the persistence and effectiveness of these molecules are influenced by several factors, including soil texture, rainfall amount and timing, and climatic conditions (Carbonari et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Mancuso et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong the herbicides registered for \u003cem\u003eEucalyptus\u003c/em\u003e cultivation, isoxaflutole stands out. It acts by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), which is essential for the synthesis of tocopherol and plastoquinone (Pallet, 1998). Inhibition of this enzyme leads to the disappearance of photosynthetic pigments, resulting in the symptom known as \u0026ldquo;bleaching,\u0026rdquo; followed by growth arrest and tissue necrosis (Pallet et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The main target species of this herbicide are grasses and some broadleaf weeds (Silva and Silva, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIsoxaflutole is classified as a pro-herbicide, as its parent molecule is not phytotoxic and herbicidal activity depends on its conversion to the active metabolite diketonitrile (DKN) (Marchiori Jr. et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Compared with isoxaflutole, DKN is more soluble (326 mg L⁻\u0026sup1;), chemically stable, and persistent in soil, with a reported half-life exceeding 56 days at pH 7.0 and 2.5% organic carbon. In contrast, the parent compound exhibits a half-life of less than two days under similar conditions (Taylor-Lovell et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Taylor-Lovell et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The persistence and spatial distribution of both compounds in the soil profile are strongly governed by soil moisture regimes and vertical transport processes, as demonstrated by recent modeling studies (Gassmann et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBecause the activation of isoxaflutole is moisture-dependent, postapplication water restriction may delay its conversion to DKN and compromise residual weed control. Under prolonged dry conditions, the herbicide may remain largely inactive in the soil until rainfall occurs, a moment that often coincides with intense weed emergence (Oliveira Jr. et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Previous studies have consistently shown that extended dry periods after application reduce isoxaflutole efficacy, particularly in soils with lighter texture (Marchiori Jr. et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn forest systems, the effects of soil moisture on isoxaflutole behavior are further modulated by soil physical attributes, rainfall timing, and surface conditions during plantation establishment. Interactions between soil texture and postapplication rainfall strongly influence herbicide persistence, weed emergence dynamics, and overall control efficiency, reinforcing the importance of site-specific management strategies in forest plantations (Gassmann et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Duque et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTherefore, this study aimed to quantify the residual activity of isoxaflutole and its active metabolite DKN in soils with contrasting textures under prolonged postapplication water restriction, linking herbicide persistence to weed control efficiency during eucalyptus plantation establishment.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eThe experiments were conducted in a greenhouse at the \u003cem\u003eN\u0026uacute;cleo de Pesquisas Avan\u0026ccedil;adas em Matologia\u003c/em\u003e (NUPAM), Faculty of Agronomic Sciences \u0026ndash; UNESP, Botucatu, SP, Brazil. Two soils with distinct characteristics were used. The first was a clay-textured soil collected from an area with different cropping systems at FCA/UNESP, and the second was a sandy-textured soil collected from a forestry production area in the municipality of Tr\u0026ecirc;s Lagoas, SP. The physicochemical properties of both soils are presented in Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePhysicochemical characteristics of the soils used in the experiments.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"11\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e\n \u003cp\u003eChemical Characteristics\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\n \u003cp\u003eSoil\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003cp\u003eCaCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\n \u003cp\u003eOM\u003c/p\u003e\n \u003cp\u003eg dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\n \u003cp\u003eP\u003csub\u003eresin\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003emg dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c5\"\u003e\n \u003cp\u003eAl\u003csup\u003e3+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c6\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c7\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c8\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c9\"\u003e\n \u003cp\u003eSB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c10\"\u003e\n \u003cp\u003eCEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c11\"\u003e\n \u003cp\u003eV%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"7\" nameend=\"c11\" namest=\"c5\"\u003e\n \u003cp\u003emmolc dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eSandy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4,4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c5\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c6\"\u003e\n \u003cp\u003e0,34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c7\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c8\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c9\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c10\"\u003e\n \u003cp\u003e26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c11\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eClay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e4,2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c5\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c6\"\u003e\n \u003cp\u003e0,57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c7\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c8\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c9\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c10\"\u003e\n \u003cp\u003e34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c11\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e\n \u003cp\u003ePhysical Characteristics\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\n \u003cp\u003eSoil\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003eSand\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003eSilt\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003eClay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"7\" morerows=\"1\" nameend=\"c11\" namest=\"c5\" rowspan=\"2\"\u003e\n \u003cp\u003eTexture\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\n \u003cp\u003eg Kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eSandy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e870\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"7\" nameend=\"c11\" namest=\"c5\"\u003e\n \u003cp\u003eSandy\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colname=\"c1\"\u003e\n \u003cp\u003eClay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c2\"\u003e\n \u003cp\u003e210\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c3\"\u003e\n \u003cp\u003e98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colname=\"c4\"\u003e\n \u003cp\u003e692\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"7\" nameend=\"c11\" namest=\"c5\"\u003e\n \u003cp\u003eClay\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe experiments were conducted in a completely randomized design (CRD) arranged in a 2 \u0026times; 5 factorial scheme, with five replications. Treatments consisted of two doses of isoxaflutole (Fordor\u0026reg; \u0026ndash; 750 g kg⁻\u0026sup1;): 0 and 150 g a.i. ha⁻\u0026sup1;, and five water restriction periods after herbicide application: 0, 30, 60, 90, and 120 days. This experimental design was applied to two soil types (sandy and clayey) and evaluated for the control of two grass species: signal grass (\u003cem\u003eUrochloa decumbens\u003c/em\u003e) and guinea grass (\u003cem\u003ePanicum maximum\u003c/em\u003e).\u003c/p\u003e\n\u003cp\u003eThe isoxaflutole dose of 150 g a.i. ha⁻\u0026sup1; was selected because it represents a commonly adopted operational rate in forest plantation establishment. The combined quantification of isoxaflutole and DKN was used to represent the biologically active fraction in soil, as both compounds contribute to residual weed suppression under field-relevant conditions.\u003c/p\u003e\n\u003cp\u003eExperimental units consisted of 2.5 L pots filled with the respective soils. Both species were sown at rates of 1.314 and 0.126 g of seed per pot, respectively, to achieve the emergence of approximately 25 seedlings of each species per experimental unit. Seeds were incorporated at a depth of 3 cm.\u003c/p\u003e\n\u003cp\u003eHerbicide application was performed immediately after sowing using an automated sprayer within a closed environment. The system consisted of a 2-meter spray boom driven by an electric motor coupled with a frequency modulator, allowing control of the application speed. The boom was equipped with four XR 110.02 VS flat-fan nozzles spaced 0.5 m apart and positioned 0.5 m above the target. The working pressure was set at 2.0 kgf cm⁻\u0026sup2;, with a travel speed of 3.6 km h⁻\u0026sup1; and a spray volume of 200 L ha⁻\u0026sup1;.\u003c/p\u003e\n\u003cp\u003eAt the end of each water restriction period, a simulated rainfall event of 20 mm was applied using the same automated system, adapted for rainfall simulation. Following the simulated rainfall, pots were irrigated uniformly to maintain soil moisture adequate for seed germination.\u003c/p\u003e\n\u003cp\u003eTo determine the efficacy and persistence of isoxaflutole, the following variables were evaluated: control percentage, shoot biomass, and soil concentrations of isoxaflutole and its metabolite DKN. Weed control was visually assessed at 15, 30, and 60 days after the simulated rainfall using a 0\u0026ndash;100% scale, where 0 corresponds to no injury and 100% to complete plant death (Velini, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). After the final control assessment at 60 days, the shoots were collected and oven-dried at 60\u0026deg;C for 72 hours in a forced-air circulation system.\u003c/p\u003e\n\u003cp\u003eThe experimental conditions were designed to simulate post-planting scenarios commonly observed in eucalyptus plantations subjected to delayed rainfall after herbicide application, as reported in studies evaluating residual herbicides under forest conditions (Marchiori Jr. et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Oliveira Jr. et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eQuantification of isoxaflutole and DKN in soil\u003c/h2\u003e\n \u003cp\u003eSoil samples for the analysis of isoxaflutole and DKN concentrations were collected seven days after the simulated rainfall for each water restriction period using cylindrical samplers 9 cm in length. Four subsamples were collected per pot, thoroughly mixed, and stored at \u0026minus;\u0026thinsp;20\u0026deg;C.\u003c/p\u003e\n \u003cp\u003eIsoxaflutole and DKN were quantified together, which does not compromise the assessment of herbicide efficacy, selectivity, or environmental behavior, as DKN is an active metabolite with herbicidal activity that rapidly transforms in soil (Taylor-Lovell et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Mitra et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Taylor-Lovell et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). For compound quantification, soils were homogenized and placed in aluminum trays for drying in an oven at 40\u0026deg;C for 48 hours. An aliquot of 7 g from each sample was weighed and transferred to plastic cartridges containing a glass fiber filter at the bottom for solution filtration, with 3 mL collection vials attached externally to collect the extracted material.\u003c/p\u003e\n \u003cp\u003eSamples were saturated with 1.5 mL and 3.0 mL of distilled water for sandy and clayey soils, respectively, and maintained under saturated conditions for 24 hours. After this period, samples were centrifuged for 5 minutes at 4000 rpm. The supernatant was then filtered through 0.2 \u0026micro;m Millipore filters and transferred to 2 mL vials for LC-MS/MS analysis.\u003c/p\u003e\n \u003cp\u003eThe LC-MS/MS system consisted of a Shimadzu Proeminence UFLC high-performance liquid chromatograph (HPLC), which allows ultrafast analysis with excellent separation performance and high reliability of results. The system was equipped with two LC-20AD pumps, an SIL-20AC autosampler, a DGU-20A5 degasser, a CBM-20A system controller (enabling fully automated operation), and a CTO-20AC column oven for temperature control. Coupled to the HPLC was a hybrid triple quadrupole 3200 Q TRAP mass spectrometer (Applied Biosystems), in which Q1 and Q3 act as mass filters, and Q2 functions as a collision cell where intact Q1 ions and fragments are further broken into smaller mass fragments. This analytical setup follows validated multiresidue protocols for the simultaneous quantification of isoxaflutole and its transformation products in complex matrices (Lan et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003eData analysis\u003c/h2\u003e\n \u003cp\u003eFor data analysis, the results were subjected to analysis of variance (ANOVA) at a significance level of p\u0026thinsp;\u0026le;\u0026thinsp;0.05, and the confidence interval (CI) was calculated using the t-test: \u003cem\u003eIC = t*DP/\u0026radic;(n)\u003c/em\u003e Where \u003cem\u003et\u003c/em\u003e refers to the tabulated t-value (p \u0026le; 0.05), SD is the standard deviation of the data, and \u003cem\u003en\u003c/em\u003e is the number of samples.\u003c/p\u003e\n \u003cp\u003eFor control and biomass data, when significant, means were compared using Tukey\u0026rsquo;s test (p\u0026thinsp;\u0026le;\u0026thinsp;0.05). For isoxaflutole\u0026thinsp;+\u0026thinsp;DKN concentrations, the data were fitted to a nonlinear log-logistic regression model as proposed by Streibig et al. (1980): \u003cem\u003ey =a/[1+(x/b )\u003csup\u003ec\u003c/sup\u003e]\u003c/em\u003e Where \u003cem\u003ey\u003c/em\u003e\u0026thinsp;=\u0026thinsp;concentration of isoxaflutole\u0026thinsp;+\u0026thinsp;DKN; \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;water restriction period (days); \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;asymptote between the maximum and minimum values of the variable; \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;period corresponding to 50% of the asymptote; and \u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;slope of the curve.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eHigher residual concentrations of isoxaflutole\u0026thinsp;+\u0026thinsp;DKN were observed in clayey soil compared to sandy soil. In sandy soil, a 50% reduction in product concentration occurred after just 1 day of water restriction, whereas in clayey soil the same reduction was reached only after 4.5 days. This difference becomes even more pronounced when considering a 90% reduction of the compounds: in clayey soil, this reduction occurred only after 103 days of water restriction, while in sandy soil it was observed after just 10 days. These results explain the higher control percentages and greater biomass reduction observed for \u003cem\u003eUrochloa decumbens\u003c/em\u003e and \u003cem\u003ePanicum maximum\u003c/em\u003e throughout the evaluation periods (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAcross all evaluated periods, the control of \u003cem\u003eUrochloa decumbens\u003c/em\u003e and \u003cem\u003ePanicum maximum\u003c/em\u003e was satisfactory (100%) in the absence of water restriction, regardless of soil texture. In other words, rainfall immediately following application ensured maximum control up to 60 days after the simulated rainfall (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). As the duration of water restriction periods after isoxaflutole application increased, the control of these species began to vary according to soil texture (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor the control of \u003cem\u003eUrochloa decumbens\u003c/em\u003e, no differences in control percentage were observed between clayey and sandy soils up to 30 days of water restriction. After this period, in clayey soil, control remained above 95% at all three evaluation times (15, 30, and 60 days after simulated rainfall \u0026ndash; DAS), even with water restriction extended to 120 days. In sandy soil, however, control decreased from 60 days of water restriction onward (83\u0026ndash;90%, depending on the evaluation time), reaching 50% at 60 DAS under 120 days of restriction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Comparable patterns have been reported in Brazilian forestry systems, where rainfall timing and eucalyptus harvest residues modulate herbicide bioavailability and field performance (Carbonari et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Duque et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA similar pattern was observed for \u003cem\u003ePanicum maximum\u003c/em\u003e, except at 15 DAS, where differences in control between the soils were recorded under 30 days of drought. At 60 days of restriction, control in sandy soil ranged from 70 to 80%, depending on the evaluation time, showing lower values than those observed for signal grass. Nevertheless, under the longest restriction period (120 days), control remained around 50%. The higher control levels of both species in clayey soil reflect the greater persistence of isoxaflutole in this texture (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRegarding shoot biomass, for U. decumbens, plant growth and development were not affected by soil texture up to 60 days of water restriction, with the lowest biomass percentages observed in both soils relative to untreated control. From 90 days onward, biomass in clayey soil remained like previous periods, showing differentiation only at 120 days. In sandy soil, biomass increased more markedly from 90 days of water restriction. For P. maximum, biomass increase occurred from 60 days of restriction in sandy soil, whereas in clayey soil this increase was significant only at 120 days (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese results, together with the concentrations of isoxaflutole\u0026thinsp;+\u0026thinsp;DKN in the soil (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), indicate that the longer the period of drought after application, the lower the herbicide activity, as it tends to remain adsorbed to soil colloids and, in the case of isoxaflutole, is less converted into DKN. According to classical studies on residual herbicides, isoxaflutole can maintain biological activity under conditions of limited soil moisture, remaining available in the soil until rainfall promotes its activation and uptake by germinating weeds (Rodrigues and Almeida, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). This behavior helps explain the maintenance of weed control observed after intermediate periods of water restriction, particularly in clayey soil.\u003c/p\u003e \u003cp\u003eThe results demonstrate greater persistence of isoxaflutole in clayey soil (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and more effective control of the species, even after prolonged periods of water restriction in this soil type (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), which is reflected in the lower shoot biomass of both grasses compared to sandy soil (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe contrasting persistence patterns observed between sandy and clayey soils have direct implications for weed management during eucalyptus establishment under irregular rainfall. In clayey soils, higher retention and slower dissipation of isoxaflutole and DKN extended the period of effective weed suppression even after prolonged water restriction. In contrast, the rapid decline in herbicide availability in sandy soils reduced residual control, increasing the likelihood of weed emergence following delayed rainfall events. These differences highlight soil texture as a key risk factor when defining herbicide-based strategies for forest plantation deployment.\u003c/p\u003e \u003cp\u003eThe lower leaching potential of isoxaflutole occurs in clayey soils, as well as in soils with higher organic carbon content. In addition to organic matter, soil pH also influences the sorption of this molecule; higher pH values are associated with lower sorption and, consequently, greater leaching potential (Mitra et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Sorption of isoxaflutole also decreases with decreasing soil organic matter content (Mitra et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Another factor contributing to greater herbicide persistence is related to clay characteristics, which have higher specific surface area and cation exchange capacity, enhancing retention of isoxaflutole in the soil (Melo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBased on soil analysis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and the results obtained in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), it can be inferred that organic matter and clay content significantly influence the persistence of isoxaflutole in clayey soils. Inoue et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), when evaluating herbicide movement in sandy and clayey soils, observed differences in the behavior of this molecule, possibly associated with variations in soil organic carbon and, to a lesser extent, pH. Marchiori Jr. et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) reported greater stability and persistence of the residual effect of isoxaflutole in clayey soil compared to sandy-loam soil, attributing these differences to variations in organic carbon and clay content (10.30 \u0026times; 3.07 mg dm⁻\u0026sup3; and 72 \u0026times; 27%, for clayey and sandy soils, respectively).\u003c/p\u003e \u003cp\u003eMarchiori Jr. et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) also demonstrated higher control of \u003cem\u003ePanicum maximum\u003c/em\u003e compared to \u003cem\u003eUrochloa decumbens\u003c/em\u003e at a dose of 180 g a.i. ha⁻\u0026sup1;, 15 days after sowing in sandy-loam soil. This difference in control between species may be explained by differences in herbicide metabolism rates. In sensitive species, the metabolic process is slower, whereas in more tolerant plants, such as eucalyptus (Adoryan et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), sugarcane, and maize (Oliveira J\u0026uacute;nior et al., 2006), the transformation of DKN into benzoic acid and CO₂ occurs more rapidly.\u003c/p\u003e \u003cp\u003eFurthermore, Marchiori Jr. et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) reported over 90% control for these species in clayey soil at doses of 230 and 270 g a.i. ha⁻\u0026sup1; of isoxaflutole, even under water restriction periods of up to 120 days. In sandy-loam soils, however, control values were lower for both species across all water restriction periods, corroborating the results obtained in the present study.\u003c/p\u003e \u003cp\u003eBiomass accumulation analysis also confirmed that control of both species over time was more effective in clayey soils. Similar results were observed by Melo et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), who evaluated shoot dry mass of sorghum (Sorghum bicolor) grown in soil columns up to 30 cm deep, subjected to surface applications of isoxaflutole (113 and 169 g a.i. ha⁻\u0026sup1;) followed by two 40 mm simulated rainfall events. Monquero et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2008b\u003c/span\u003e) also reported albinism symptoms in sorghum plants grown in similar soil columns up to 25 cm, observing that control percentage increased proportionally with the amount of applied rainfall.\u003c/p\u003e \u003cp\u003eFrom a forest management perspective, the greater persistence of isoxaflutole observed in clayey soils under prolonged water restriction has important operational implications. Previous studies conducted in eucalyptus systems have shown that soil texture, organic matter content, and rainfall timing are key drivers of herbicide behavior and weed control efficacy (Carbonari et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Marchiori Jr. et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Recent modelling approaches further indicate that soil moisture dynamics strongly govern the fate and vertical distribution of isoxaflutole and DKN in soil profiles, affecting the duration of effective weed suppression (Gassmann et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this context, extended herbicide persistence in clayey soils may increase the effective weed control window in eucalyptus plantations established under irregular rainfall, reducing the need for early post-emergence interventions. Conversely, the lower persistence observed in sandy soils reinforces the importance of adjusting application timing and management strategies according to site-specific soil and climatic conditions, as also highlighted in recent forestry studies (Duque et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEven after prolonged post application drought, isoxaflutole maintains effective residual weed control in clayey soils, whereas sandy soils exhibit rapid loss of persistence, increasing the vulnerability of eucalyptus plantations to early weed interference under irregular rainfall conditions.\u003c/p\u003e \u003cp\u003eIn this context, the combined assessment of chemical persistence and biological response under extended dry periods advances previous studies by explicitly linking soil texture, moisture regimes, and residual herbicide performance in forest production systems.\u003c/p\u003e \u003cp\u003eAlthough the experiment was conducted under greenhouse conditions, the imposed water restriction periods and rainfall simulation were designed to reproduce post-planting scenarios commonly observed in commercial eucalyptus plantations subjected to delayed or irregular rainfall, allowing consistent interpretation of herbicide behavior under operationally relevant conditions.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eFrom an operational perspective, these findings indicate that isoxaflutole use in sandy soils under forecasted dry periods should be carefully planned, with adjustments in application timing or complementary management practices, whereas clayey soils provide a wider safety margin for residual weed control during eucalyptus establishment.\u003c/p\u003e \u003cp\u003eSoil texture should therefore be considered a primary factor when defining the reliability of isoxaflutole residual control during eucalyptus establishment under uncertain rainfall conditions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eF.G.O.S. contributed to conceptualization and overall leadership of the study.E.D.V. contributed to project administration, investigation, and provision of resources.C.A.C. contributed to resources.N.C.B. contributed to data curation, methodology, and data analysis.R.N.C. contributed to data curation, methodology, and data analysis.J.T.F.T. contributed to data curation.B.F.G. contributed to data curation.All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors acknowledge the institutional support provided by Universidade Estadual \u0026ldquo;J\u0026uacute;lio de Mesquita Filho\u0026rdquo; (UNESP) during the development of this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdoryan ML, Bendeck OB, Gelmini GA (2002) \u003cem\u003eEfic\u0026aacute;cia e seletividade do herbicida isoxaflutole na cultura de Eucalyptus grandis\u003c/em\u003e. In: Congresso Brasileiro da Ci\u0026ecirc;ncia das Plantas Daninhas. p. 576\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarbonari CA, Gomes GLGK, Krenchinski FH, Sim\u0026otilde;es PS, Castro EB, Velini ED (2020) Dynamics and efficacy of sulfentrazone, flumioxazin, and isoxaflutole herbicides applied on eucalyptus harvest residues. New Forest 51(4):723\u0026ndash;737\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarbonari CA, Velini ED, Silva JRM, Bentivenha SRP, Takahashi EN (2010) Efic\u0026aacute;cia da utiliza\u0026ccedil;\u0026atilde;o de gr\u0026acirc;nulos de argila como ve\u0026iacute;culo para a aplica\u0026ccedil;\u0026atilde;o a\u0026eacute;rea de sulfentrazone e isoxaflutole em \u0026aacute;rea de implanta\u0026ccedil;\u0026atilde;o de eucalipto. 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Pestic Biochem Physiol 62(2):113\u0026ndash;124\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodrigues BN, Almeida FS (1998) Guia de herbicidas, 4th edn. Edi\u0026ccedil;\u0026atilde;o dos Autores, Londrina\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilva AA, Silva JF (2007) T\u0026oacute;picos em manejo de plantas daninhas. Universidade Federal de Vi\u0026ccedil;osa, Vi\u0026ccedil;osa, MG\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStreibig JC (1980) Models for curve-fitting herbicide dose response data. Acta Agriculturae Scand 30:59\u0026ndash;64\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTaylor-Lovell S, Sims GK, Wax LM, Hasset JJ (2000) Hydrolysis and soil adsorption of the labile herbicide isoxaflutole. Environ Sci Technol 34(19):3186\u0026ndash;3190\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTaylor-Lovell S, Sims GK, Wax LM (2002) Effects of moisture, temperature, and biological activity on the degradation of isoxaflutole in soil. J Agric Food Chem 50(20):5626\u0026ndash;5633\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVelini ED (1995) \u003cem\u003eEstudos e desenvolvimento de m\u0026eacute;todos experimentais e amostrais adaptados \u0026agrave; matologia\u003c/em\u003e. PhD thesis, Universidade Estadual Paulista, Jaboticabal\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Pre-emergence herbicide, weed interference, soil–herbicide interaction, residual activity, silviculture","lastPublishedDoi":"10.21203/rs.3.rs-9586051/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9586051/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eForest plantations, particularly eucalyptus, are highly sensitive to weed interference during the establishment phase, making the use of residual herbicides a common management practice. However, irregular rainfall after planting may delay herbicide activation and alter its persistence in the soil. This study evaluated the residual activity of isoxaflutole and its active metabolite diketonitrile (DKN) on the control of \u003cem\u003eUrochloa decumbens\u003c/em\u003e and \u003cem\u003ePanicum maximum\u003c/em\u003e in soils with contrasting textures under different post-application water restriction periods. A greenhouse experiment was conducted using sandy and clayey soils in a completely randomized design, arranged in a 2 \u0026times; 5 factorial scheme, with isoxaflutole applied at 150 g a.i. ha⁻\u0026sup1; and water restriction periods of 0, 30, 60, 90, and 120 days. After each restriction period, a simulated rainfall of 20 mm was applied. Weed control, shoot dry biomass, and soil concentrations of isoxaflutole\u0026thinsp;+\u0026thinsp;DKN were evaluated. In the absence of water restriction, complete control of both species was observed in both soil types. Increasing periods without rainfall reduced herbicide efficacy, particularly in sandy soil. Isoxaflutole\u0026thinsp;+\u0026thinsp;DKN persistence was consistently higher in clayey soil, resulting in sustained weed control and lower biomass accumulation even after prolonged water restriction. These results demonstrate that soil texture and post-application moisture conditions strongly influence the residual performance of isoxaflutole and should be considered when planning weed management strategies during the establishment of eucalyptus plantations under conditions of delayed or irregular rainfall. These findings provide practical support for defining herbicide strategies in eucalyptus plantations established under irregular rainfall, highlighting soil texture as a key factor determining the effective window of residual weed control.\u003c/p\u003e","manuscriptTitle":"Residual activity of isoxaflutole under water restriction in contrasting soil textures of forest plantations","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 08:20:22","doi":"10.21203/rs.3.rs-9586051/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"af7f1639-88ed-4ebb-ab4d-8aba8f54b5ec","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[{"type":"editorAssigned","content":"","date":"2026-05-04T06:39:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-04T06:38:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"New Forests","date":"2026-05-01T12:23:31+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T08:20:22+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 08:20:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9586051","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9586051","identity":"rs-9586051","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}