Smooth- Digitaria ischaemum. Large crabgrass has a membranous ligule that is truncate and has a jagged appearance. The inflorescent consists of a panicle of branches with spikelets arranged in two rows of a flattened rachis.
Smooth crabgrass has a membranous ligule that is truncate and often has a smooth appearance.
The sheath has no hairs. The inflorescent consists of a panicle of digitate branches with spikelets arranged in two rows of a flattened rachis. Overall, smooth crabgrass is similar to large crabgrass with the exception that smooth crabgrass is not as coarse or tall, has no hairs around the sheath or on the leaves, and is more reddish or purple. Both germinate at higher soil temperatures, usually later in the season, when the residual activity of some soil-applied herbicides may have dissipated to the point that the grasses may escape. Finally, reliance on ALS herbicides has increased crabgrass problems as these herbicides have no activity on smooth crabgrass and only fair activity when applied to small large crabgrass.