The Authentic Reason Greeks Paint Trees White: Protecting Against Fungi and Bacteria

For centuries, a distinctive sight in Greek landscapes has been the white-painted trunks of trees, especially in orchards and along roadsides. This long-standing tradition holds practical reasons beyond mere aesthetics. As an agronomist with a university degree, I can explain the primary purpose behind this practice, which is predominantly to protect tree trunks from fungi and bacteria. While some of the commonly cited reasons, such as protection from insects and temperature regulation, have been debunked as urban legends, the actual benefits are scientifically grounded.

The Scientific Purpose: Protecting Against Fungi and Bacteria

The practice of painting tree trunks in Greece is an ancient agricultural technique that dates back many years. Traditionally, the white paint used is a mixture of copper sulphate hydrate (approximately 10%) and hydrated lime (calcium hydroxide, approximately 10%), diluted in water. This mixture is known as Bordeaux Mixture, a fungicide and bactericide that has been used in agriculture for centuries.

Bordeaux Mixture is effective because it contains copper ions, which are toxic to a wide range of bacteria and fungi. When applied to the tree trunks, this mixture helps to prevent fungal and bacterial infections that can significantly damage the trees. Some of the diseases that can be controlled include:

Phytophthora strains Verticillium strains Fusarium spp. Botryosphaeria spp. Eutypa spp. Esca disease Phomopsis disease Various bacterial diseases, including strains of Pseudomonas

Protection Mechanism: Adhesion and Active Ingredient

The efficacy of the Bordeaux Mixture relies on two significant components:

Copper Sulphate Hydrate: This ingredient provides the active copper ions that are crucial for preventing fungal and bacterial growth on the tree trunks. Copper ions are highly toxic to many pathogens, making the mixture effective in creating a protective barrier. Hydrated Lime (Calcium Hydroxide): This component serves as a binding agent, helping to adhere the copper ions to the tree trunks over an extended period. This ensures the mixture remains effective for long-term protection.

As the mixture dries, the copper ions form a protective layer on the tree trunks, thereby preventing the entry of harmful pathogens. This practice is widely utilized in many Mediterranean countries to protect fruit-bearing trees such as olives, citrus, and almonds.

Contradictions and Misconceptions

It is common for people without agricultural knowledge to attribute the practice of painting tree trunks to less scientific reasons such as protecting against insects or regulating temperature. These claims are largely based on urban legends, rather than facts. The following reasons are not supported by scientific evidence:

Protection from Insects: The bright white color does deter some insects but there is no significant evidence that it effectively protects trees from all pest problems. Temperature Regulation: While the color reflects sunlight and helps keep the trunks cooler in hot weather, this is not a major factor in tree protection. More modern temperature-regulating techniques are more effective. Visibility: The primary purpose is not for visibility, although it does make the trunks more visible. The main benefit is the protection against pathogens.

Therefore, it is important to understand that the primary purpose of painting tree trunks is to prevent fungal and bacterial infections, a practice that is both scientifically proven and widely employed in agricultural settings.

Conclusion

Painting tree trunks with a mixture of copper sulphate hydrate and hydrated lime is a time-honored tradition in Greece and other Mediterranean countries. This practice is not just an aesthetic choice but a critical method for protecting trees from deadly fungal and bacterial diseases. While it may not offer complete protection against all pests, it significantly enhances the health and productivity of the trees, making it a valuable tool in modern agricultural practices.