What herbicide was effectively used to control water hyacinths post-1947 without toxicity to humans or animals?

2,4-D is an herbicide that has been widely utilized for the management of aquatic weeds, including water hyacinths, especially after its introduction in the late 1940s. This systemic herbicide is selective, which means it targets certain plant species while being less harmful to non-target organisms, including humans and animals.

The mode of action for 2,4-D involves disrupting plant growth by mimicking natural plant hormones, leading to uncontrolled growth and eventual death of susceptible plants. Its effectiveness and relative safety in terms of toxicity to humans and animals made it a preferred choice for controlling water hyacinths in aquatic environments.

The other options, while related to weed control or management, do not fit the criteria of being an effective herbicide specifically for water hyacinths without significant toxicity concerns.