The question is checking which herbicide fits both conditions at once: used specifically in rice, and applied after the weeds have already come up (post-emergence), while still being safe for the rice crop (selective).
- Pretilachlor: Works on germinating weed seeds soon after transplanting, so it behaves as a pre/early post-emergence herbicide, not one sprayed on established weeds.
- Butachlor: Similar to pretilachlor, it is applied close to transplanting to stop weed seedlings from establishing, again not a true post-emergence spray on grown weeds.
- Bispyribac Sodium: Sprayed around 15 to 20 days after transplanting rice, once weeds are clearly up and growing, and it selectively kills grasses, sedges and broadleaf weeds while leaving the rice crop unharmed.
- Tembotrione: A genuine post-emergence herbicide, but its crop label is maize, not rice.
Bispyribac Sodium is the right choice because it matches both requirements of the question: it is used in rice, and it is sprayed as a true post-emergence, selective treatment.
Let's summarize:
- Pretilachlor and butachlor act early, mostly on germinating weed seeds in rice.
- Bispyribac sodium is rice's standard selective post-emergence herbicide; tembotrione belongs to maize.
So the correct option is Bispyribac Sodium.