Why are systemic herbicide treatments most effective when applied in late summer or early fall?

Answer

The tree is naturally moving photosynthesized sugars down toward the roots

During late summer and early fall, the tree is preparing for dormancy by translocating sugars downwards, which effectively carries the systemic herbicide directly to the living root tissues.

Why are systemic herbicide treatments most effective when applied in late summer or early fall?
plantmethoderadicationcontroltree of heaven