Smooth crab grass, Digitaria ischaemum

Life Cycle



Reproducing only by seed.


Stems are 5 - 120 cm long, erect, spreading, or lying on the ground and rooting at nodes (a) in contact with the soil.


Has smooth, hairless leaf blades, and upper leaf sheaths usually smooth and hairless, but the lower ones may be somewhat hairy; ligule (g) also membranous but usually a bit longer (2 - 3 mm), and there is a tuft of long hair on either side of the leaf-base (h) of the lower leaves; no auricles.

Flowers and Fruit

Inflorescence almost identical to that of Large crab grass (A) but usually with only a single whorl of spikes at the end of the stem (as illustrated in A). Flowers from August to September.

Roots and Underground Structures

Fibrous root systems.


Both kinds of crab grass are common in southern Ontario but they also occur sporadically in northern and northwestern Ontario. Both occur in row crops and other fields, waste places, gardens and lawns.


Corn yield loss (%)*: 1 % at 1 plant/m2 3 % at 5 plant/m2 Soybean yield loss (%)*: 1 % at 1 plant/m2 3 % at 5 plant/m2 *assumes that the weed has emerged with the crop and has been left uncontrolled all season.

Distinguishing Features

Before heading out, they are distinguished by their tapered leaf blades, their split sheaths with hairless margins (c), their membranous ligules (d, g) with no auricles, their more or less hairy lower leaf sheaths (b), and their either hairy or smooth blades. After heading out, the slender finger-like spikes are distinctive.


Smooth crabgrass is not known to be toxic.

Human Health Issues

Smooth crabgrass is not a known allergen.

Forage Quality

No information exists at this time.

Species Benefits

No information available at this time.

Often Mistaken For

Large crabgrass (DIGSA), Fall panicum (PANDI)

Power Ranking Corn

Power Ranking

↑ 7


Power Ranking Soybeans

Power Ranking

↑ 10


Biological Control

Currently none available for this weed. For the latest research on biological weed control:

Biopesticide Control

Currently none available for this weed in corn and soybean. Corn gluten meal will inhibit germination of crabgrass seeds in turf.

Herbicide Resistance

No documented cases of herbicide resistance to date. For more information on weed resistance:

Figure #1.

Large crab grass: A. Plant. B. Leaf base. C. Side view. D. Back view of a portion of spike with several spikelets. [b]Smooth crab grass: E. Leaf-base of lower leaf.[/b]

Figure #2.

Ligule: Membranous.

Figure #3.

Leaf blade: Hairless on both sides.

Figure #4.

Leaf sheath: Smooth, leaf sheath margins are also hairless.

Figure #5.

Seed head.

Figure #6.

Mature plant.

Bio Control Agents

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