Why is basal bark treatment not recommended for wood species larger than 6" in diameter?

Basal bark treatment is a method of applying herbicide directly to the lower portion of the tree trunk, typically targeting species of a certain size for effective weed management. The effectiveness of this treatment diminishes significantly for wood species larger than 6 inches in diameter primarily because of the physical characteristics of the bark on larger trees. As trees grow, their bark becomes thicker and more protective, creating a barrier that hinders the penetration of the herbicide into the living tissue of the tree. This reduced penetration means that the herbicide may not reach its intended target cells, resulting in an ineffective treatment. Therefore, for trees larger than this size, alternative methods are generally recommended to ensure that the herbicide can effectively control the target species.