Garlic and Garlic-Based Products for Sustainable Agriculture

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Garlic and garlic-based products

Use of garlic extract and substrate in vegetable crops for protection against pathogens and biostimulation of their growth.

Description

Garlic has been cultivated for centuries and is renowned for its pungent taste and medicinal properties. Its sulfur compounds, such as allicin, contribute to its distinctive flavor and various health benefits, including antibacterial, antifungal, and antioxidant properties.

These products have attracted attention as natural alternatives to synthetic fungicides and pesticides in agriculture, showing effective antifungal and nematicidal activity against various plant pathogens.

Beyond its antifungal properties, garlic exhibits biostimulant effects on plants, promoting growth, development, and stress tolerance. Studies suggest that garlic extracts induce a defense state in plants, increasing their resistance to pathogens and environmental stresses. These garlic-based biostimulants offer promising prospects for improving the quality and yield of crops while reducing dependence on synthetic fertilizers and pesticides.

Molecules of interest and extraction

Molecules of garlic extract

The molecules present in garlic extracts and substrates mainly consist of allicin and diallyl sulfide. Several other molecules of interest are also found such as ajoene, garlicin, and eruboside. To access these molecules for further use, several extraction methods are employed to obtain adequate access.

Extraction

Maceration in oil or water

This process involves crushing the garlic cloves and immersing them in oil or water. The mixture is slowly homogenized, and the residue is subsequently filtered to obtain a liquid extract.

To make the extract, 1 kg of garlic is crushed and left in 300 ml of oil or water for 3 days. This mixture is then filtered and diluted with water to 5 or 10%.

Distillation

Crushed garlic cloves immersed in water can be subjected to a steam distillation process to obtain an extract that can then be dissolved in vegetable oil for later use.

The process to obtain the extract is to take 1 kg of crushed garlic in 500 ml of water in a distillation apparatus. Then distill the mixture until the oily extract stops. Next, the extract is diluted to 5%.

Decoction

1 kg of crushed garlic cloves is immersed in 500 ml of water, and the mixture is gently boiled for 15 to 20 minutes. The cooled mixture is then filtered to obtain the decoction.

Garlic juice

The juice directly extracted from 1 kg of crushed garlic cloves can be used in agriculture. This juice can be diluted in water when used.

Garlic substrate

All the remaining parts of garlic production can be used as garlic substrate. The cut stems after harvest, the remaining garlic part after maceration or juice, etc.

Products available on the market

The main player in this industry is Ecospray, producing 3 products in granular and liquid form, mainly as nematicides. The company also has partnerships with Certis Europe, Biogard IT, etc.

Cost

There are many variations in formulations, such as maceration extracts, suspension concentrates, etc. Costs vary and range from €16 to €45/L, about €100 per 25 kg bag for the solid formulation. The cost may vary depending on the country and reseller. The prescribed dose for commercial products is 25 kg/ha.

The "homemade" manufacturing cost of the extract individually is extremely variable depending on source availability. If access to all necessary materials is possible, the cost can be much lower compared to direct product purchase.

Costs can be mitigated by using rejected garlic cloves that are not fit for market entry.

Regulation of garlic use in agriculture

A peer review committee of the EFSA (European Food Safety Authority) reviewed the regulation on the use of garlic extract products in agriculture in June 2020. The conclusions indicate:

• Uses of garlic extract according to representative uses as repellent, insecticide, and nematicide on a wide range of crops in agriculture, horticulture, green spaces, as proposed at the European Union (EU) level, demonstrate sufficient efficacy against target organisms.

• No critical areas of concern were identified in the field of mammalian toxicology.

• Overall, the use of garlic is not considered a serious issue in terms of ecological and environmental toxicity, and it shows sufficient efficacy against diseases.

Therefore, the use of garlic extract products for agricultural purposes has been authorized in the European Union.

Garlic in Biocontrol

Mode of action

• Garlic and garlic-derived products, containing specific components such as allicin and diallyl disulfide, act as a defense mechanism for plants by disrupting the outer layer of harmful germs and interfering with their crucial processes, ultimately leading to their destruction.
• These components have a notable impact on plant growth by influencing cell division, maintaining hormonal balance, and regulating gene activity.

Use and application

Currently, no information is available indicating use under field conditions.

Research has evaluated the use of garlic juice under controlled conditions, with concentrations ranging from 50 to 1000 µg/ml.

For example, in one scenario, tomato leaves from 3-week-old plants were treated by spraying with diluted garlic juice, specifically containing 200 to 800 μg/ml against tomato late blight (Phytophthora infestans) and downy mildew of cucumber (Pseudoperonospora cubensis). This treatment involves preventive application, which can be administered either by foliar spray or watering.

For the product containing diallyl disulfide molecule (emulsifiable formulation), it is applied at 10 L/ha, performing a direct soil application.

Targeted diseases and pests

Garlic-based products in general are effective against:

• downy mildew of tomato caused by Phytophthora infestans.
• Downy mildew of cucumber caused by Pseudoperonospora cubensis.
• Wilt caused by Fusarium sp.
• Nematodes causing galls.
• Soil fungi.

Moreover, garlic root exudates have been noted to stimulate protective enzymatic systems of other plants, promoting their growth and reducing their susceptibility to pests and diseases.

Biostimulant effects

Known for their growth-promoting compounds such as starch, vitamins, allicin, and diallyl disulfide, garlic extracts have proven to be remarkable biostimulants for plants, manifesting a range of beneficial effects on their growth, development, and overall health.

• Through application methods such as foliar spraying and fertigation with an aqueous garlic extract, for example, this extract acts as a stimulant for various RedOx and physiological reactions in plants, impacting nutrient absorption, photosynthetic pigments, and root activity, thus leading to significant increases in leaf and root length.
• The addition of garlic substrate in the short term can modify soil biochemistry and increase organic carbon input by creating optimal habitats for microorganisms. These changes stimulate biological processes, increasing soil and plant productivity as well as microbial diversity. At optimal concentrations, it also triggers plant defense responses inducing resistance against fungal infections.
• The formulation of products from garlic extracts proves promising, preparing plant defense systems for advanced protection against fungal diseases. Moreover, the extract's ability to control plant hormonal balance encourages fruiting, flowering, and overall yield increases.

Advantages and limitations

Exploring the advantages and limitations of using garlic and garlic-based products is essential to understand their effectiveness against the growing problem of pest resistance, especially considering the EU's strict requirements on diverse formulations.

Advantages

• Antifungal properties.
• Strengthening of plants' natural defenses.
• Improvement of soil structure and enrichment with essential nutrients.
• Stimulation of healthier and more vigorous crop growth.
• Versatile application (use in various forms).
• These products are authorized in Organic Farming.
• Non-toxicity to the environment.

Limitations

• Availability.
• Short-term protection.
• Non-selectivity (they may affect beneficial organisms).
• Development of pest resistance.

Use of garlic in cucumber cultivation

Crop associations

In addition to extracting molecules with biocontrol benefits, growing garlic itself provides benefits when associated with other crops. Researchers have demonstrated that a change in soil structure occurs when monoculture is practiced for a long time, soil biological diversity declines, leading to a reduction in bacteria populations and an increase in plant pathogenic fungi.

However, in the specific case of cucumber, association with garlic showed an increase in soil diversity, as follows:

• Increase in competitiveness between beneficial and pathogenic fungi, leading to self-regulation.
• Decrease in fungi, especially pathogens, and increase in bacterial population.

As part of the study on crop association, it was conducted under greenhouse conditions with the following:

• One cucumber plant and one garlic plant were planted 5 cm apart in barrels.
• The experiment included four treatments:
  • No crop (Cont).
  • Cucumber monoculture (C).
  • Garlic monoculture (G).
  • Garlic and cucumber association (CG).

However, this experiment could be extended to a broader context, with cucumber plantations at a non-experimental scale, which is why it is mentioned in

Number of bacteria, actinomycetes and fungi found in each treatment

this article.

These mechanisms related to garlic cultivation improved the soil microbial environment and effectively mitigated damage caused by soil impoverishment in terms of diversity in monoculture and the increase of pathogens (in this case fungi), thus promoting cucumber seedling growth.

Other researchers also found that garlic:

• Stimulates cucumber growth and development: Application of garlic substrate significantly increased seedling height, leaf area, stem diameter, and root length of cucumber.

• Improves nutrient availability: Addition of garlic substrate improved soil nutrient availability, notably nitrogen, phosphorus, and potassium.

• Improves soil microbial community structure and diversity: Application of garlic substrate increases diversity and abundance of soil microorganisms, especially beneficial bacteria and fungi that promote plant growth and inhibit pathogens.

• Effectively inhibits Fusarium wilt, a destructive fungal disease affecting cucumbers.

• Increases cucumber yield: Application of garlic substrate resulted in a significant increase in cucumber fruit yield and quality.

The greatest decrease in disease incidence percentage and benefits were observed with a higher dose of garlic substrate addition at a ratio of 5:100 (g/100 g soil).

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