Read the label. Forms a gas that kills small weed seedlings at the soil surface. Intended to be applied with a mulch layer over the top, to retain the gas. If label does not describe controlling sprouting, existing perennial weeds with it you may not get the desired result.

Thanks Bob, (happy early BD)
I did read the label, I was hoping someone may have had experience with both Bishops Weed & it's use around critters.
Jill
Hope we have another beautiful day, a gardeners delight!

While it does have some post-emergent characteristics (it can alter or impede root development), Casoron/dichlobenil is considered a primarily pre-emergent herbicide. That means it will have minimal effect on existing plants or weeds - its primary mode of action is to interfer with the development of seeds or seedlings. You will probably get more effective control by manually removing the bishop's weed or using a broad spectrum,post-emergent like RoundUp later in the season. It is also not registered for use on bishop's weed.

Personally, I wouldn't choose to use it. It is somewhat volatile and caustic and should be used with protective clothing, gloves, and eyewear and should not be used around pets or domesticated animals (states this very clearly on the label).

Some maintenance companies sprinkle it directly on top of the bark mulch without covering it. This enables it to be tracked about by animals and people. Applied this way the gas can burn the lower leaves of existing shrubs like rhododendrons. Covered or not, it can leach downslope and kill the lawn or other soft tissued perennials.
Roundup is a better option after the Bishop's Weed has sprouted in the Spring as GardenGal said.

Thanks for the advice. I originally bought it to use between bricks on a small patio & it worked great so I'll continue to use it for that type of application. Jill

Aka Norosac. Remember Serutan...Natures spelled backwards?

lost me, please explain, Jill

Casoron is also sold under the brand name Norosac.
Casoron spelled backwards.
I remember buying a bag of it years ago and don't know if it's still available under that name. I don't get out much anymore since I retired four years ago.