Chamberbitter (Mimosa Weed)

In order to respond to the many garden questions I receive, I’ve assembled a crack team of Master Gardeners to help me. Theresa, Stacy, Caryn and Shannon have myriad different garden skills and interests and I can count on them to know the answer to most of the queries we get via e-mail.

When Stacy e-mailed all of us a panicky personal question a few days ago, I knew it had to be a stumper. “Help! My lawn has been invaded by little mimosa seedlings. I have tried everything to get rid of them but nothing seems to work. Are any of you familiar with this weed?”

Familiar?? Heck, I’m on a first name basis with this pest. My neighbor Gus brought it to my attention a few years ago in his lawn. Now he spends a half-hour each week pulling it from his flower beds and his fescue.

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.

Stacy’s lack of success controlling niruri is duplicated by weed scientists. No herbicide will knock it out quickly and permanently. Dr. Tim Murphy, my Extension service weed guru, says repeated applications of an herbicide that contains 2,4-D (Weed-B-Gon, Weed Stop, Wipe-Out, etc) will control it, particularly if you start spraying when the weed is young.

The yellow, ball-like seeds of niruri develop under the leaves. They need very warm soil in order to germinate so you won’t notice the seedlings until mid-summer. Researchers say pre-emergence herbicides that contain atrazine (Purge) on centipede lawns and isoxaben (Greenlight Portrait,

Be persistent in battling common chamberbitter

By Larry Williams

Thu, Aug. 29, 2002

In your lawn and landscape beds, do you have the weed that has leaves resembling those of a miniature mimosa tree?

On the undersides are many small, round balls. If you don't have this troublesome weed, you are certainly the exception. It's called chamberbitter and it is very common in North Florida.

The bad news is there is little information on the biology of this difficult-to-control weed. But it can be controlled if you are persistent.

Chamberbitter, botanically known as Phyllanthus urinaria, is found throughout Florida. It germinates from early summer through early fall. The most distinct feature of this weed is the numerous, small, smooth, round fruits attached to the undersides of its stems.

Chamberbitter is very competitive in our lawns. It produces a great number of viable seeds and it has good shade-tolerance but will grow in full sun.

Early detection and action are important. Once it sets seed, control is that much more difficult. To begin the battle against chamberbitter, apply a pre-emergent herbicide when the soil starts warming up, usually around the first of May.

According to the 2002 University of Florida Pest Control Guide for Turfgrass Managers (available at 2006 Pest Control Guide), atrazine or isoxaben (Gallery) provides good control. Isoxaben (Gallery) is safe for all the warm-season grasses. Atrazine, however, is not registered for use on bahia grass or bermuda grass. Atrazine is safe to use on centipede grass and St. Augustine grass when used according to label directions.

It is important to note, however, that atrazine can be used only twice in a year. Also, it should never be applied in the root zone of any ornamental plant.

Once the chamberbitter weeds have germinated, a post-emergent herbicide may be necessary. Nonselective herbicides containing glyphosate, such as Roundup, are effective but only in areas such as landscape beds where the weed is isolated and you can keep the spray off desirable plants. In lawns, you must use selective post-emergent herbicides that won't hurt the grass.

Barry Brecke, UF-IFAS Extension weed scientist, recommends atrazine or simazine applied twice, with applications spaced about three weeks apart.

Atrazine + bentazon (sold under the trade name, Prompt) may be a little more effective. Again, plan on two applications spaced about three weeks apart. Products containing mixtures of 2,4-D, dicamba, MCPP or MCPA (Weed-B-Gon, Weed Stop, etc.) applied twice, seven days apart, may also be used at recommended rates.

If you do decide to use any of the herbicides mentioned, follow the label directions to the letter.

Mechanical pulling is always an option. However, be sure not to shake the soil from the root system, as it will just spread the seeds.

For more information about gardening in our area, visit the University of Florida IFAS Leon County Extension Web site at http://leon.ifas.ufl.edu. 

*Larry Williams is the horticulture extension agent for University of Florida IFAS Extension in Okaloosa County.

Photo by Alabama Cooperative Extension.