Chamberbitter (Mimosa Weed): Identification and Control

My Master Gardener team helps answer queries. When Stacy panicked about "little mimosa seedlings" invading her lawn, I knew it was a stumper. I'm on a first-name basis with this pest – neighbor Gus brought it to my attention years ago. He spends 30 minutes weekly pulling it from beds and fescue.

The weed: niruri (Phyllanthus urinaria), now called chamberbitter. "Niruri" = "break stone" in Spanish. Mature plant is a small shrub in South America/Asia, used for kidney stones. In my lawn, constant mowing keeps it 3 inches tall, looking exactly like mimosa leaves.

Control Challenges

No herbicide knocks it out quickly/permanently. Dr. Tim Murphy (UGA weed guru): repeated applications of 2,4-D (Weed-B-Gon, Weed Stop, Wipe-Out) control it, especially when young.

Yellow ball-like seeds develop under leaves. Need very warm soil to germinate → seedlings appear mid-summer. Pre-emergence: atrazine (Purge) on centipede; isoxaben on all turfgrasses – apply early May.

Pulling works for many. Discard plants immediately – not on compost pile.

Q&A

Q: How do I kill chamberbitter in lawn and flower beds?
A: Glyphosate (Roundup) kills it but avoid nearby foliage. In lawn: broadleaf weedkiller (Weed-B-Gon, Weed Stop) twice, 7 days apart.

Best prevention: Apply isoxaben pre-emergent late April and mid-June in areas not being seeded. Read label exactly.

See also Phyllanthus: A Growing Problem in Georgia Landscapes.

chamberbitter