During what phase is it often more difficult to control perennials?

Controlling perennials can be particularly challenging during the flowering phase due to several factors. In this stage, perennials are often fully established, having developed extensive root systems that allow them to access nutrients and water more efficiently than during earlier phases. This increased vigor and resilience make them less susceptible to herbicides.

Additionally, during flowering, plants may focus energy on reproduction rather than vegetative growth, which can result in tougher, more robust structures that are harder for herbicides to penetrate effectively. The production of flowers and seeds can also serve to prioritize the plant's survival, allowing it to recover more rapidly from attempted control measures. Consequently, the flowering phase represents a critical time when many plants can withstand herbicide applications that might have been more effective during their earlier growth stages.