chamberbitterby Larry Williams, UF/IFAS Extension Agent

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 diligence.

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 and 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 seedlings germinate and emerge.

Atrazine or isoxaben (both sold under various brand names) provide “good” pre-emergence control (defined as 80-90 percent efficacy) of chamberbitter.

Isoxaben is safe for all of our warm-season lawn grasses. However, atrazine will injure or kill bahiagrass and bermudagrass. Atrazine is safe to use on centipedegrass and St. Augustinegrass when used according to label directions.

Once weeds have germinated, a post-emergence herbicide may be necessary. Atrazine applied twice, spaced about three weeks apart can be used in centipedegrass and St. Augustinegrass lawns.

Products containing mixtures of 2, 4-D, dicamba and MCPP (these are three-way mixtures) 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 centipedegrass and St. Augustinegrass but are safe in bermudagrass, bahiagrass and zoysiagrass 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 plants: trifluralin plus isoxaben (Snapshot TG), prodimine (Barricade) and isoxaben (Gallery).

Once the weeds have germinated, your only post-emergence options are glyphosate, non-selective herbicides. When using a non-selective herbicide, be sure to protect your desirable plants. Direct the spray to the weed only and prevent spray from drifting onto your desirable ornamentals.

Pulling and disposing of weeds is an option. But be sure to not shake soil from the root system. This may spread the seeds.

Appropriate use of mulch in plant beds can eliminate or reduce weed population. It is very important that chamberbitter not be allowed to set seed by using all appropriate control methods.

The following link from Clemson Cooperative Extension provides some of the best information on controlling this weed that I’ve seen.  http://www.clemson.edu/extension/hgic/pests/pdf/hgic2314.pdf

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