Monosodium methanearsonate (MSMA) weed killer is a post-emergent herbicide for use in home lawns to control a range of annual grass-type weeds. It is sometimes also known as MAMA or DSMA on some herbicide labels.

...
MSMA weed killer is used for controlling crab grass and other grassy weeds.

When to Apply

Herbicides containing MSMA are most effectively applied when grassy weeds such as crab grass and Dallis grass have emerged in the early spring and are actively growing. Repeat applications may be required through the late spring and summer. Initiating control in late summer or fall when the weeds are mature will not be successful. MSMA is most effective on younger weeds.

How to Use

...
Irrigating treated areas can help to mitigate possible damage to desirable turf.

Formulations of MSMA may be liquid or granular. For granular applications, the soil should be moistened prior to use. An additional 1/2 inch of water should be applied two days after the application.

Precautions

...
Drifting of liquid MSMA herbicides will harm desirable grasses.

MSMA herbicides can damage lawns if used at higher than recommended rates. Even at recommended rates, it can harm some turf grass species. Make sure to read the label entirely before applying any herbicide containing MSMA.