Evaluation of wood vinegar from the pyrolysis of wood residues of Gmelina arborea and its application as herbicide for weed control

Abstract

Wood vinegar (WV) produced via biomass pyrolysis, presents an organic alternative for weed control. This study aimed to: (i) determine the physical properties and elemental composition analysis of WV, and (ii) evaluate the efficacy of WV from wood residues of Gmelina arborea produced with slow pyrolysis to control weeds under a Cupressus lusitanica Christmas tree plantation. WV was dissolved in water at 75% and applied in doses of 1000, 3000 and 5000 L ha^-1, with the synthetic herbicide Basta® (glufosinate-ammonium) as a control. The efficacy of WV on weeds was visually evaluated from 0 (not injury) to 100 (plant death). Treatments with 3000 and 5000 L ha⁻¹ doses caused rapid desiccation of grass and broadleaf weeds, achieving 85 to 88% visual injury. Biomass reduction of 40% can be obtained when WV is applied at high doses (3000 and 5000 L ha^-1) on mature grass-dominated weeds, showing effects comparable to synthetic herbicide. While WV effectively reduced weed biomass, it was insufficient to completely remove mature weeds.

Full Article

Evaluation of Wood Vinegar from the Pyrolysis of Wood Residues of Gmelina arborea and its Application as Herbicide for Weed Control

Jair Granados-Chacón  ,^a Roger Moya  ,^a,* Jaime F. Quesada-Kimzey  ,^c and Allen Puente-Urbina  ,^d

Wood vinegar (WV) produced via biomass pyrolysis, presents an organic alternative for weed control. This study aimed to: (i) determine the physical properties and elemental composition analysis of WV, and (ii) evaluate the efficacy of WV from wood residues of Gmelina arborea produced with slow pyrolysis to control weeds under a Cupressus lusitanica Christmas tree plantation. WV was dissolved in water at 75% and applied in doses of 1000, 3000 and 5000 L ha^-1, with the synthetic herbicide Basta® (glufosinate-ammonium) as a control. The efficacy of WV on weeds was visually evaluated from 0 (not injury) to 100 (plant death). Treatments with 3000 and 5000 L ha⁻¹ doses caused rapid desiccation of grass and broadleaf weeds, achieving 85 to 88% visual injury. Biomass reduction of 40% can be obtained when WV is applied at high doses (3000 and 5000 L ha^-1) on mature grass-dominated weeds, showing effects comparable to synthetic herbicide. While WV effectively reduced weed biomass, it was insufficient to completely remove mature weeds.

DOI: 10.15376/biores.21.3.8366-8382

Keywords: Grass control; Organic herbicide; Grass weeds; Wood vinegar doses; Bioherbicides; Acid-pyrolysis

Contact information: a: Escuela de Ingeniería Forestal, Instituto Tecnológico de Costa Rica, Apartado 159-7050, Cartago, Costa Rica. Email: [email protected]; b: Escuela de Ingeniería Forestal, Instituto Tecnológico de Costa Rica, Apartado 159-7050, Cartago, Costa Rica; Email: [email protected]; c: Escuela de Química, Instituto Tecnológico de Costa Rica, Apartado 159-7050, Cartago, Costa Rica. Email: [email protected]; d: Escuela de Química, Instituto Tecnológico de Costa Rica, Apartado 159-7050, Cartago, Costa Rica. [email protected]; *Corresponding author: [email protected]

This article is dedicated to the memory of Jaime F. Quesada-Kimzey who died in March 2026

Graphical Abstract

Wood vinegar was used for weeds control under a tree plantation applied in doses of 1000, 3000 and 5000 L ha-1, with synthetic commercial herbicide as a control. Treatments with 3000 and 5000 L ha⁻¹ doses caused rapid desiccation of grass and broadleaf weeds, achieving 85-88% visual injury during first seven days

INTRODUCTION

Herbicides rank as the third most toxic group of pesticides, after insecticides and fungicides (Mahmood et al. 2016). The most widely used herbicides in the world are the broad-spectrum and non-selective chemicals glyphosate, glufosinate-ammonium and paraquat (Maliang et al. 2022). Glyphosate inhibits enzymes essential for aromatic amino acid biosynthesis, ultimately causing plant death through starvation (Agostini et al. 2020). It is commonly applied to eliminate vegetation after harvest or before crop establishment (Ramírez-Muñoz 2021). Similarly, glufosinate is used for post-emergence and pre-plant burndown (Dayan et al. 2019). Its rapid phytotoxicity results from the accumulation of reactive oxygen species, which trigger lipid membrane peroxidation (Takano et al. 2019, 2020). Paraquat exhibit very fast uptake, producing reactive oxygen species that cause desiccation of plant tissues (Hawkes 2015). Paraquat has been banned in several countries due to health risks (Bang et al. 2017; Camargo et al. 2020; Albrecht et al. 2022).

The use of pesticides has been increased in recent decades due to the increment of crops production; unfortunately, the risks associated with their use have outweighed their beneficial effects (Mahmood et al. 2016). Latin America has been no exception. This region is one of the world’s main agricultural areas with a very intensive use of pesticides (Hilber et al. 2024). This situation is aggravated by the fact that research and legislative efforts on pesticide use and management in the different countries are not as exhaustive as their temperate counterparts (Daam et al. 2019). Extensive research has been conducted on the problems associated with synthetic herbicides. Among these issues are: weed resistance, exposure of workers and health issues (Hsiao et al. 2021; González-Moscoso et al. 2023; Flafel et al. 2024), residues on food (Soares et al. 2021) and animal feed (Heydebreck 2021), and the effects on the environment (Daam et al. 2019; Kanissery et al. 2019) biodiversity (Brühl and Zaller 2021; El Jaouhari et al. 2023), water (Syafrudin et al. 2021; Mugudamani et al. 2023) and soils (Rose et al. 2016; Dennis et al. 2018).

Costa Rica, a small country in Central America, despite being known worldwide for its environmental policies, is one of the largest consumers of pesticides (Ramírez-Muñoz et al. 2017). Costa Rica has had intensive use of the synthetic herbicides glyphosate and paraquat (Montero-Rojas 2018; Staudacher et al. 2020; Viales-López 2024), which are the second and third most imported pesticide by volume, respectively (Vargas-Castro 2021). Training of pesticide applicators on proper use practices and protection should be encouraged to reduce health and safety risks to workers and the environment (Hilber et al. 2024). However, training and awareness programs may not effectively translate into behavioral changes (Yuantari et al. 2015; Fuhrimann et al. 2020).

On the other hand, there is a growing need for sustainable weed management approaches that support economic profitability, reduces environmental impact and respond to social demands (Cordeau et al. 2016). In this context, bioherbicides, products of natural origin for weed control (Bailey 2015), align with circular economy principles, as they rely on renewable resources and can reduce dependence on synthetic agrochemicals, while they often are more environmentally benign (Hasan et al. 2021) and have the potential to cause rapid plant degradation (Cordeau et al. 2016). The use of WV is a potential solution to the pressure to adopt sustainable agricultural practices that minimize over-reliance on the use of chemicals (Ouattara et al. 2023). For example, in Costa Rica, D-limonene, as well as pine and rosemary extracts were found to be effective and even faster than a synthetic herbicide in post-emergence weed control (Aguirre et al. 2020a). Organic compounds used for weed control include flavonoids, terpenoids, alkaloids and quinones, and phenolic acids (Ramírez-Muñoz 2021).

Recently, wood vinegar (WV), produced by pyrolysis of biomass, has attracted interest for its use as a bioherbicide (Aguirre et al. 2020a). WV consists mostly of water (80 to 90%) and more than 200 organic compounds categorized as acids, alcohols, ketones, aldehydes, esters, furans and nitrogenates (Aguirre et al. 2020a,b). The herbicidal properties of WV are attributed to the large amount of acids, especially acetic acid, which usually occupies the largest proportion, and phenols (Liu et al. 2021a; Maliang et al. 2022). It has been shown that WV, at high concentrations and application doses, presents effective herbicidal effects for the management of weeds (Liu et al. 2021b; Chu et al. 2022). However, only a few studies as an herbicide in natural conditions have been conducted (Aguirre et al. 2020). In China, WV from elm (Ulmus spp.) and apple (Malus × domestica Borkh) tree branches pruning waste has been demonstrated to control weed species under field conditions, similar to a non-selective herbicide, by causing fast desiccation on plants due to high content of acids (Liu et al. 2021a,b). Similarly, in Spain, Aguirre et al. (2020a) concluded that WV helps to control the development of annual plants by damaging the entire epidermis and its stomatal cells.

The presence of phenolic compounds in WV confers antifungal and pest control properties, increases the permeability of agrochemicals into leaf tissue, and enhances the effectiveness of chemical pesticides when used in combination. WV has been found to be effective against houseflies in some publications and is an alternative to agrochemicals and therefore, it can be used as a bioherbicide and potentially replace synthetic chemical herbicides (Ouattara et al. 2023). The phenols, organic acids, carbonyls, alcohols, and other organic acids present in pyroligneous acid influence its herbicidal activity (Liu et al. 2021a), and these are not present in synthetic components. Acetic acid, the main component of pyroligneous acid and a naturally occurring component of this product, has been used in agriculture for weed control.

In Costa Rica, pyrolysis of biomass has the potential to provide a solution to wood waste management (Aguirre et al. 2019b) while producing WV, as it is the major constituent of pyrolysis liquid (Jaworski et al. 2016). The second most planted tree in Costa Rica is Gmelina arborea Roxb. ex Sm (Instituto Nacional de Estadística y Censos 2022). The wood processing of this tree has been reported to be inefficient and producing great amount of residues (Espinoza-Durán and Moya 2013). For this reason, the yields and process of slow pyrolysis of G. arborea wood residues had been investigated. Recent research of G. arborea residues (Moya et al. 2024; Granados-Chacón et al. 2025) showed that yields of charcoal were 26 to 28%, WV from 28 to 30%, and non-condensable gases about 37%. However, these studies presented the importance and characteristics of solid products (charcoal) as energy and agriculture applications.

WV, produced by the slow pyrolysis of G. arborea wood residues, shows a high yield but no information has been presented about its potential as a natural alternative of weed control due to its herbicidal properties. So, further research is needed to elucidate its efficacy to control weeds. Then the objectives were established: (i) to determine the physical properties and chemical composition of WV, and (ii) to evaluate the efficacy of WV in three different doses from wood residues of Gmelina arborea produced with slow pyrolysis to control weeds under a Cupressus lusitanica Christmas tree plantation, evaluating visual injury and biomass reduction of weeds.

EXPERIMENTAL

Wood Vinegar Preparation

Wood vinegar (WV) was produced from the slow pyrolysis of wood residues of Gmelina arborea in a semi-industrial reactor prototype (Granados-Chacón et al. 2025). Wood board-ends were residues from the secondary wood processing with dimensions of 4 to 25 cm long and 12 to 32 mm thick and a moisture content of 16%. A cylindrical reactor of 58 cm diameter, 88 cm long, and 232 L capacity with a glass fiber insulating jacket was used. The pyrolysis process began at 25 °C and rate of temperature rise of 10 °C/min until reaching 450 °C. The process finished when the syngas flame was over, and then the reactor was kept closed until the temperature reached 25 °C, where the time varied from 5 to 6 hours. Detailed chemical composition of Gmelina arborea is reported elsewhere (Moya et al. 2024). The pyrolytic gases were cooled through a system of two coolers made of two helical coil heat exchangers. The first heat exchanger was cooled with air at room temperature and a second cooler with a closed water circuit moved by a pump, where wood vinegar was collected. Liquids were collected after each cooler. Non-condensable gases (syngas) continued its flow by pipe for the heating of the pyrolysis reactor (See Fig 2 in Granados-Chacón et al. 2025). This reactor presented a charcoal yield of 26 to 31% and a WV yield from 27 to 32%.

Wood Vinegar Physical Properties and Elemental Composition Analysis

The WV physical properties of pH, electric conductivity (EC), and density were determined by the Centro de Investigaciones Agronómicas (CIA) of the Universidad de Costa Rica (UCR). The concentration of elements (N, Cu, Fe, Zn, Mn, B, P, Ca, Mg, K and S) in pure WV was determined with an analysis of organic fertilizers. Nitrogen (N) was determined by MicroKjeldahl wet digestion with H₂SO₄ and colorimetric determination in the Flow Injection Analyzer (FIA) and P, Ca, Mg, K, S, Fe, Cu, Zn, Mn, B by digestion with HNO₃ and determination by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES).

Site and Soil Conditions

This experiment was conducted during the first months of the wet season (from May to June of 2024) in a Cupressus lusitanica Christmas tree plantation (9°50’29.2″ N 83°47’05.2″ W, Fig. 1a) of approximately 1500 m² and 18 months old located in Paraíso, Cartago province, at 1130 masl. Grass was the dominant weed group.

Soil was characterized as clay loam with 32.3% clay, 36.3% sand, 31.3% silt, and 4.23% organic matter. Soil chemistry was characterized by 5.20 pH, acidity 1.12 cmol (+) L⁻¹, EC 0.20 mS cm⁻¹, Ca 10.95 cmol (+) L⁻¹, Mg 2.05 cmol (+) L⁻¹, K 0.53 cmol (+) L⁻¹, CEC 14.66 cmol (+) L⁻¹, acid saturation 7.77 %, P 44.7 mg L⁻¹, Zn 3.87 mg L⁻¹, Cu 22.7 mg L⁻¹, Fe 390 mg L⁻¹, Mn 26.0 mg L⁻¹, C 2.96%, N 0.34%, and a C:N ratio of 8.83.