Bioherbicide

Technical articles

Chemical weeding Weeding

A bioherbicide is a product composed of natural substances used to control weeds. These are weeding products derived from living organisms. The presence of weeds leads to a decrease in yield, so their populations must be reduced, but the products mostly used (glyphosate, 2,4-dichlorophenoxyacetic acid…) leave residues and pollute soils and water. Bioherbicides are a less harmful alternative for ecosystems and could also be an alternative for farms practicing organic farming that rely on mechanical weeding .

Types of bioherbicides

Bioherbicides can be composed of various natural substances: bacteria, fungi, plant substances (essential oils)… There are bioherbicides specific to a weed, but also non-specific bioherbicides.

Essential oils

Essential oils are the subject of much research for weeding.

• Examples of effective oils: essential oils containing pelargonic acid such as geranium essential oil, or vinegar (acetic acid).
• Mode of action: Allelopathic effect inhibiting germination and growth of weeds, comparable to some chemical herbicides on species such as field mustard (Sinapis arvensis).

The only bioherbicide product currently authorized in large crops is pelargonic acid (for example the product “Beloukha”).

Pelargonic acid is a fatty acid found for example in geranium. This acid dries out and dehydrates the plant by destroying its epidermis. It is a non-selective bioherbicide. It acts in just a few hours, however its effectiveness decreases over time.

In viticulture, it is used for shoot thinning and under-row weeding.

It is not authorized in organic farming because it can potentially impact the crop environment.

APEO Project

In Belgium, the company APEO (Agronomical Plant Extracts and Essential Oils) develops a bioherbicide based on essential oils.

In 2011, to address issues of herbicide-resistant weeds and risks related to the use of phytosanitary products, they decided to start focusing on essential oils as a control method.

There was first a preselection of 91 essential oils among the 3000 existing, based on price and availability, to test them as fungicides and herbicides.

They were first tested as fungicides and this showed that some are toxic to plants, hence the idea to use them as herbicides.

Three oils among those tested were selected because they showed interesting properties against monocotyledons, dicotyledons, mosses and horsetails.

The formulation of the essential oil is important to influence the product’s effectiveness because it influences the mode of action and stability, and it can help protect the essential oil against unfavorable factors that would limit its action.

Research on the product formulation was carried out between 2015 and 2016. The initial formulation was based on chemical co-formulants, which contradicted the goal of offering an environmentally friendly product different from synthetic phytosanitary products already on the market. They were therefore replaced by biological co-formulants.

Tests were then conducted in greenhouses, showing that the product with biological co-formulants was very effective against dicotyledons and somewhat less so against monocotyledons.

Field trials

The highest dose after one month is more effective than pelargonic acid and as effective as glyphosate.

The product is effective against dicotyledons and somewhat less so against monocotyledons, especially on fairly young stages.

Results after 5 years of trials

On 40 species of dicotyledons, there is equal or even superior effectiveness compared to the pelargonic acid-based product, and in 4 out of 7 cases, this is also true for monocotyledons.

Thus, there is good effectiveness for a large number of weeds, and this remains the case two months after treatment application.

Persistence of action

Persistence of action is an important parameter for an herbicide. On dicotyledons, after 100 days there is still good persistence of action, superior to that of pelargonic acid.

Moreover, this product apparently reduces the weed seed bank from one year to the next, which is not the case with pelargonic acid.

Mode of action

The action is multi-site: several parts of the cell are attacked, so the product acts through several modes of action.

When the treatment is applied, organelles cluster in the middle of the cell and there is damage to cell walls, mitochondria, a desiccation effect…

As the product is rapidly biodegraded, within 48 to 72 hours, there is no impact on the subsequent crop.

Various products under development

A first product is a ready-to-use formulation, the registration dossier was submitted in 2024. The goal is to start marketing it in 2026 in the United States and in 2027 in Europe.

A second product is still a prototype, with a much more concentrated formulation so that application volumes per hectare are reasonable (5 to 10L).

There is also a project to develop a selective product against dicotyledons, as current products are non-selective.

Bacteria and fungi

Researchers are working on the use of bacteria and fungi to control weeds.

Uses of bioherbicides

Bioherbicides limit weed populations by producing toxic metabolites or by affecting cellular functions of plant cells, notably by degrading membranes, causing dehydration, or inhibiting germination… .

The mode of action resembles a host/pathogen mechanism or can also resemble the phenomenon of allelopathy.

Furthermore, for the bioherbicide to be effective, various parameters must be considered such as the phenological stage of the targeted weed, environmental conditions, and the dose of bioherbicide applied.

Bioherbicides can be used for:

• Specific weeding or spot application: fences (livestock), yards, private gardens
• Weed management on large-scale crops before sowing
• Cover control (using a lower dose)
• Potato desiccation: chemical desiccation is the most used method. But a method consisting of shredding potato tops then completing with a bioherbicide could be effective and would reduce the use of chemical products. For this method, the application of Beloukha can be a solution. However, it is a product that requires good implementation conditions (water volume, climatic conditions…) for good results.

• Pruning of vines and fruit trees (control of suckers in arboriculture, shoot thinning of vine, suckers of apple trees, pear trees, cherry trees)
• Control of grass cover in vineyards

Method of use

For the bioherbicide to be effective, it must be used at the right time and under good conditions:

• Between April and September, after seed dormancy breaks;

• Temperature above 15°C;

• It is recommended to treat at 3 to 4 leaf stage, not exceeding 6 leaf stage

• Avoid rain: a minimum delay of 2 hours is recommended between application and rain to prevent product runoff

• It is advised to treat when the sky is bright as this allows better desiccation;

• Two to four applications per year should be made according to product registration criteria;

• It is necessary to treat regularly over the years, which helps reduce the seed bank in the soil;

• Wet the entire plant for use as an herbicide

• Follow the dosage indicated on the label.

Effectiveness of bioherbicides

• Good effectiveness against dicotyledons
• Less effective against monocotyledons
• Especially effective on young stages and during plant growth

However, depending on the compounds used, doses applied, and targeted weeds, bioherbicides are not necessarily effective and their environmental impact is not always well evaluated.

Cost

Bioherbicides are generally more expensive to purchase than chemical herbicides, due to production costs, small industrial scale, and sometimes lower effectiveness requiring repeated applications or higher doses.