Tar oils

Tar oils are complex chemical mixtures obtained through the distillation of wood or coal tar. In the context of plant protection, they act as broad-spectrum contact pesticides. Historically, these substances have served as a foundational tool for orchard management, providing a reliable method to suppress pest populations during the dormant stage of plants.

The primary mechanism of action is physical rather than metabolic. Upon application, the oil forms a persistent film over the target organisms, covering their spiracles and egg surfaces. This creates an impermeable barrier that prevents oxygen exchange, leading to the asphyxiation of insects, mites, and their eggs. This physical mode of action significantly reduces the risk of resistance developing in pest populations.

Tar oils are widely used in orchards and nurseries to target overwintering pests. Key targets include scale insects, mites, aphids, and psyllids. Furthermore, their application helps in the sanitation of fruit tree bark, as they can effectively manage certain fungal pathogens and epiphytic growths like mosses and lichens that shelter pest larvae during the winter.

Proper application timing is critical for these products. They should only be applied when trees are dormant, as the oil film can inhibit photosynthesis and respiration in active leaves, causing severe phytotoxicity. Application must be thorough, ensuring that all bark crevices are covered, as this is where pests typically hide during the colder months.

Safety and environmental precautions are essential when handling tar oils. Operators should wear appropriate protective equipment to avoid skin contact and inhalation. Due to their oil-based nature, they should be applied with caution near water bodies to prevent surface film formation. Storage should be in a cool, ventilated area away from oxidizing agents and open flames to ensure chemical stability.