Why must protectant fungicides often be applied repeatedly throughout a fungal disease period?

Protectant fungicides are designed to form a barrier on the surface of the plant to prevent fungal infections. However, one key characteristic of these fungicides is that they do not penetrate deeply into the plant tissue. As a result, they only provide protection to the areas that have been directly sprayed. Any plant parts that are not treated will remain vulnerable to fungal attack.

Additionally, protectant fungicides can also degrade over time when exposed to environmental factors such as sunlight. Ultraviolet light from the sun can break down these chemicals, diminishing their effectiveness. Furthermore, exposure to oxygen can also lead to the degradation of certain protectant fungicides, further shortening their active life on treated surfaces.

Given these factors, it is essential to apply protectant fungicides repeatedly throughout a period of fungal disease. This repeated application ensures that the protective barrier remains intact and effective against new fungal infections that could occur on both treated and untreated parts of the plant. By understanding these characteristics, pesticide applicators can implement effective disease management strategies while ensuring the health and productivity of their crops.