Which of the following noxious weeds can be controlled by digging and tilling up the plants?

The ability to control noxious weeds through digging and tilling depends on their life cycle and growth habits. Smooth dock, as a perennial weed, can be effectively managed by these mechanical methods. Digging up the plants can remove the root system, which is essential since these weeds tend to regrow from their roots if they are not completely removed. Tilling can also disrupt their growth by burying the roots and preventing them from accessing sunlight, which is crucial for their survival.

In contrast, the other weeds listed exhibit characteristics that make them less suitable for control through such methods. For example, Canada thistle has extensive root systems that can regenerate quickly if any part of the root is left in the soil. Field bindweed is also resilient, with deep-rooting systems that are difficult to eliminate through mechanical means alone. Teasel can be managed by pulling or digging, but it often requires careful timing and follow-up treatments due to its capacity for rapid regrowth. This highlights why smooth dock is the best choice for control through digging and tilling.