Do you have any photos?

Not sure about isoxaben but you don't want to treat just yet. Chamberbitter doesn't come up until middle June to July and the pre-emergent is only good for about 6 weeks. The best time to treat is probably late May. If you travel down to Mobile, try Lesco now under the name of John Deere Landscaping on Hwy 90 just off of I-65. They are pretty knowledgeable and carry a good selection of herbicides.

Walter describes it as:

The weed has a tongue-twisting name: niruri (Phyllanthus urinaria). In later years, scientists have started calling it chamberbitter but under either moniker it can be a major nuisance in your landscape. Niruri in Spanish literally means "break stone". The mature plant is a small shrub which grows widely in South America and Asia. There, it is used as an herbal remedy for kidney stones. In my lawn, constant mowing keeps it three inches tall and looking exactly like a mimosa leaf.

More info at the link below. Google "Phyllanthus urinaria" to see pictures.

Here is a link that might be useful: Walter Reeves on Chamberbitter