One of the worst weeds we have in the lawn and the landscape beds from midsummer through early fall is chamberbitter (Phyllanthus niruri). Some know it by the names niruri, gripeweed or little mimosa, which best describes its appearance.
I get asked about this weed more than any other this time of year. It comes up everywhere, and it is very prolific. Just one plant can release thousands of seeds. And it can do this in two weeks from the time it comes up.
Chamberbitter germinates in hot, dry weather during late spring and early summer. Once established, it is extremely tolerant of drought. It can survive even the most inhospitable conditions.
The majority of pre-emergence herbicides do a very poor job of keeping them from germinating. The typical dinitroaniline herbicides such as Preen, Surflan, Balan, Crabgrass Preventer, pendimethalin (Halts) and Dimension are basically useless in controlling chamberbitter.
The key is to do the right things at the right time, including herbicides and cultural practices.
For the lawn, the only thing that works to prevent chamberbitter from coming up and to kill existing weeds is atrazine. Atrazine works as a pre- and post-emergence weed killer. It comes in a liquid and a granular and is sold in weed-and-feed fertilizers.
It can be used on dormant or growing centipede, St. Augustine and zoysia, but Bermuda must be dormant for it to be effective.
Liquids, granular, and some weed-and-feeds containing atrazine are not labeled for green zoysia, but one weed-and-feed that most homeowners are familiar with, Bonus S, is also labeled on centipede and St. Augustine.
Use the atrazine a couple of times during the growing season to prevent chamberbitter from ever coming up. For labeled turfgrasses, make the first application around the middle of April, then follow it up with another application about three months later.
The second application is the most important because most of the chamberbitter will come up when it really gets hot during the summer.
For post-emergence control in centipede and St. Augustine, spot spray with liquid atrazine. Treat the lawn early in the season because weeds are easier to kill when they are young.
For post-emergence control in Bermuda and zoysia, pull up the weeds or repeat applications of a mixture of 2,4-D, MCPP, and dicamba (Weed-B-Gon, Weedstop, Weed Killer for Southern Lawns, etc).
For pre-emergence control in ornamental beds, the best herbicides are isoxaben (Gallery, Green Light Portrait), isoxaben + trifluralin (Snapshot), benefin + oryzalin (XL, Amaze), or prodiamine (Stagreen Crabgrass Preventer, Barricade).
Again, begin the applications in April and follow up about three months later. The granular easier to apply around sensitive flowers.
For post-emergence control, the only options are hand-pulling or direct spraying with Roundup or some other nonselective herbicide.
Be careful not to get the herbicide on desirable plants.
One of the most important cultural practices to help control chamberbitter is to maintain a 2- to 4-inch layer of mulch in flower beds. Chamberbitter seeds are small, so not many of the plants will survive if they have to penetrate a thick layer of mulch.
We are coming to the end of the weed- and grass-growing season, but you can make a weed-and-feed application (no later than Sept. 15) to fertilize the lawn, prevent and kill existing chamberbitter and other weeds, and prevent more weeds from coming up for the next three to four months.
If you don't use herbicides to control weeds, keep chamberbitter cut or pulled to keep it from putting out seed. Chamberbitter will die when we get a frost, and that is about two months away.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.