Do you have the weed that resembles miniature mimosa trees? If so, you’re not alone. This common, troublesome weed is called chamberbitter or botanically Phyllanthus urinaria. It can be controlled with correct timing and persistence.
Chamberbitter is a summer annual that requires warm soil conditions to germinate. It has numerous, small, round fruit attached to the undersides of its leaf stems.
Attempt control measures before chamberbitter produces seed. Once the round fruit are seen on the leaf stems, successful control becomes difficult or impossible.
To begin the battle against chamberbitter, apply a pre-emergence herbicide around mid April to May 1. This will be just before the seedlings germinate and emerge. Atrazine (sold under various brand names) or isoxaben (Gallery) provides “good” pre-emergence control (defined as 80-90% efficacy) of chamberbitter. Isoxaben is safe for all of our warm-season lawn grasses. However, atrazine will injure or kill bahia grass and Bermuda grass. Atrazine is safe to use on centipede grass and St. Augustine grass when used according to label directions.
Once the weeds have germinated, a post emergence herbicide may be necessary. Atrazine applied twice spaced approximately three weeks apart can be used in centipede grass and St. Augustine grass lawns. Products containing mixtures of 2, 4-D, dicamba and MCPP (such as Trimec Southern) applied twice, seven days apart may also be used at recommended rates. Some 2, 4-D, dicamba and MCPP products will severely injure or possibly kill centipede grass and St. Augustine grass but are safe in Bermuda grass, bahia grass and zoysia grass lawns, based on label directions. Most herbicides are not safe to use in lawns during warmer summer temperatures. Always read and follow label directions and precautions when using any herbicide.
With the exception of isoxaben, do not use the herbicides mentioned above in plant beds. The following pre-emergence herbicides are useful in controlling chamberbitter in ornamental plantings: trifluralin + isoxaben (Snapshot TG), prodimine (Barricade) and isoxaben (Gallery). Once the weeds have germinated, your only post-emergence options are glyphosate, non-selective herbicides, such as Roundup. When using a non-selective herbicide, be sure to protect your desirable plants, direct the spray to the weed only and prevent the spray from drifting onto your desirable ornamentals.
Pulling and disposing of the weeds is an option. But be sure to not shake the soil from the root system. This might spread the seeds. Appropriate use of mulch in plant beds can eliminate or reduce weed populations. It is very important that chamberbitter not be allowed to set seed by using all appropriate control methods.