There is a weed I have noticed for years and never knew its name. Recently, calls are coming in questioning this weed’s identity. It grows short in the grass and gets tall around landscape beds. What is this mystery weed?

Native to Asia and found throughout the tropics, chamberbitter (Phyllanthus urinaria) is a summer annual with thin, smooth-margined, oblong leaves. The leaves are arranged in two rows on branchlets. It is also known as “gripeweed,” “leafflower” or “mimosa weed.”

In Thomasville, everyone is calling it chamberbitter. It actually looks similar to another weed called Long Stalk Phyllanthus. However, chamberbitter seeds are directly touching the stalk while the seeds of Long Stalk Phyllanthus are connected by a small stem.

So, how should we control this thing? Control is best achieved through an integrated use of mechanical, cultural and chemical methods. I will discuss each:



Mechanical control

This involves the physical removal of weeds from the soil. My Uncle Jerry refers to this as BH-10: Both hands, 10 fingers. The advantage of mechanical control is preventing the weed from reaching maturity and setting seeds. This is best accomplished when the weeds are small. Additionally, this allows us to avoid chemical drift onto non-target plants like shrubs. Chamberbitter has a well-developed taproot and in moist soil can easily be pulled up in areas where chemical control would be risky.



Cultural control

Cultural control is the prevention of weeds through proper lawn management practices. An example of this would be proper cutting height for your turf. Although chamberbitter will sometimes grow down in the turf, the continuous cutting allows the grass to outcompete the weeds. The best defense against weeds is a turf not stressed by disease, insects, drought and nutrient imbalances.  Within landscape beds, apply three inches of mulch in the spring to block light from germinating seeds.

Chemical control

Herbicides can be used before chamberbitter emerges (pre-emergence) or after it emerges (post-emergence). As an annual weed, chamberbitter germinates from seed, produces seed and dies all in one season. For pre-emergent control, Atrazine can be applied to St. Augustine and centipedegrass lawns in late spring after green-up since chamberbitter is a summer annual. Do not apply Atrazine during the green-up period and into the root zone of landscape plants.

Atrazine can also be used for post-emergence control in the same grasses. It is most effective when weeds are young. You can make two applications spaced a month apart. Do not apply it when temperatures are above 90 degrees F, or the turf might be injured.

As with your landscape, the best choice for controlling existing chamberbitter is RoundUp (Glyphosate). Glyphosate moves through the entire plant and kills it. Keep in mind that it is also a non-selective herbicide that will damage any plant it contacts. In a landscape bed situation, make sure you are not close to other plants — especially in windy conditions.

You can prevent drift by using a low-pressure spray. To create low pressure with a hand pump sprayer, use fewer “pump ups” to create a larger droplet size.  Smaller droplet size results in more herbicide drift.



Information from this article was taken from “Chamberbitter” article from Clemson Extension, the UGA Master Gardener’s Handbook, and the Georgia Pest Management Handbook Homeowner’s Edition 2012.

For additional questions, contact me at 225-4130.