Virginia Tech Weed Identification Guide

Smooth Crabgrass: Digitaria ischaemum

Weed Description: Summer annual, having a prostrate or ascending growth habit, with leaves and sheaths that do not have hairs and stems that do not root at the nodes. Found throughout the United States.
Seedling:  Sheaths and blades not hairy, few hairs at mouth only, with a jagged membranous ligule. Seedlings are upright, leaves are rolled in the bud, and the first leaf blade is lanceolate to linear.
Stems: Prostrate or lying on the ground with tips ascending (decumbent) up to 60 cm long, branching at lower nodes but not rooting.

Flowers:   Seedhead composed of 2-6 branches (spikes) at the top of stems, each 10 cm long. Spikelets 1.8-2.1 mm long, 0.8-0.9 mm wide, in two rows along the spike, with short mushroom-like hairs.

Leaves:  Blades 5-14 cm long, 2-7 mm wide, without hairs. Sheaths are without hairs and closed, with hairs in the collar region only. Ligules are 1-2 mm long, membranous with even margins. Leaves and sheaths may turn dark red or maroon with age.

Roots:   Fibrous root system.

Identifying Characteristics:   Sheath and leaves without hairs, mushroom-like hairs on spikelet. May be distinguished from Large Crabgrass (Digitaria sanguinalis) by the absence of hairs on the leaves and sheath, and only a few hairs found in the collar region. Additionally, smooth crabgrass does not root at the nodes like large crabgrass.