Large crab grass, Digitaria sanguinalis

Life Cycle

Annual

Propagation

Reproducing only by seed.

Stems

5 - 120 cm (2 in. - 4 ft) long, erect, spreading, or lying on the ground and rooting at nodes (a) in contact with the soil.

Leaves

Leaves numerous near the base of the plant and scattered along the stems, 4 - 20 cm long, 5 - 10 mm wide and gradually tapered towards the pointed tip; leaf blades and leaf sheaths sparsely to densely soft-hairy; the hair (b) standing more or less straight out; leaf sheaths split, the margins (c) hairless and overlapping; ligule (d) membranous, 0.5 - 2 mm long; no auricles

Flowers and Fruit

Inflorescence finger-like, with several thin, slender, spikes (e) in a whorl at the top of the stem (A), or more usually with 2 or 3 sets of branches from the upper 2 - 4 cm of stem; each spike (“finger”) flattened and with the single-seeded spikelets (f) closely arranged along only one side (C, D); seeds purplish-green and ridged lengthwise. Flowers from July to September.

Roots and Underground Structures

Fibrous root systems.

Habitat

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.

Competitiveness

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.

Toxicity

Large crab grass is not known to be toxic.

Human Health Issues

Large 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

Smooth crabgrass (DIGIS), Proso millet (PANMI), Witch grass (PANCA)

Power Ranking Corn

Power Ranking

↑ 8

 

Power Ranking Soybeans

Power Ranking

↑ 11

 

Biological Control

Currently none available for this weed. Visit http://res2.agr.ca/Lethbridge/weedbio/index_e.htm#toc 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: http://www.plant.uoguelph.ca/resistant-weeds/


Figure #1.

[b]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.


Figure #2.

Ligule: Membranous.


Figure #3.

Leaf blade: Hairy on both sides.


Figure #4.

Leaf sheath: Hairy, yet the margins are hairless.


Figure #5.

Seed head.


Figure #6.

Mature plant.