Crabgrass

Digitaria sanguinalis (L.) Scop.

Synonyms - Panicum sanguinale

Family: - Poaceae.

Names:

Digitaria is from the Latin digitus meaning finger and refers to the finger like seed head.
Crabgrass - because it growth habit resembles a crab.

Other names:

Summer grass - because if grows and flowers in summer.

Summary:

Creeping stemmed, striped sheath, annual grass with rough leaves and a seed head of 3-10 purplish fingers. 100-1000 mm tall. Sometimes with a purplish tinge.

Description:

Cotyledons:

One

Leaves:

Emerging leaf rolled in the bud.
Mainly on the stems.
Blade - Green or tinged with purple, narrowly oval, 30-300 long by 3-14 mm wide. Wavy, slightly thickened and roughened edges. Flat, soft, rough to touch on both surfaces, limp and weak. Rounded or contracted near the base. Tapers to a point. Hairless or a few tubercle-based hairs near the base or on the upper and lower surface. Midrib whitish.
Ligule - Membranous, flat or ragged on top. 1-2 mm long. With a few hairs behind it.
Auricles -
Sheath - Striped. Sometimes has tubercle (wart) based hairs on the lower leaf sheaths.

Stems:

Creeping, soft, tufted, sometimes erect or with a knee like bend near the base. 100-1000 mm tall. Nodes are hairy, otherwise hairless. Often channelled on one side. Roots at the nodes. Branched at the lower nodes, unbranched at the upper nodes.

Flower head:

Raceme. 2-12 fingers, 30-300 mm long, initially erect but later spreading outwards. Main axis 3 angled, 20-40 mm long, and more or less in 2 rings (whorls). Branch axis is small, rough, winged (1 mm wide). Spikelets in pairs or threes on unequal stalks, pressed along one side, slightly overlapping and all the way to the base of the fingers.

Flowers:

Spikelets - Pale green to purplish, 2.5-3.5 mm long by 0.7-0.9 mm wide, lance shaped, 2 flowered. Pointed tip. Overlapping stalks of varying lengths. Fall to ground intact on maturity. Hairless or hairy but not silky hairy.
Florets - Flattened.
Glumes - Lower, triangular, tiny, less than 0.5 mm long. Upper one has 3 smooth nerves, hairy, acute tip and a third to half the length of the spikelet (1-2 mm). Usually has fine hairs between the nerves and on the edges.
Palea - Similar length to the lemma. Pointed tip.
Lemma - Lower one, 2-3.5 mm long, as long as spikelet. 5-7 nerves with 2-3 nerves near each edge and a midrib in the centre. Nerves rough to touch at least in the upper part. Edges hairy or rough. Fine, low lying silky hairs often with a frill of hairs.
Upper (fertile) lemma almost the same size as the lower, pointed tip, smooth, hairless, oval to oblong, hardened.
Stamens -
Anthers -

Seeds:

Roots:

Fibrous. Roots at the stem nodes.

Key Characters:

Spikelets paired and all the way to the base of the 'fingers'. First glume is present. Sterile (lower) lemma is rough to touch on the nerves.

Biology:

Life cycle:

Annual. Flowers November to April.
Germinates mainly in spring and makes rapid growth over the summer quickly covering the ground and competing with companion species.

Physiology:

It is a C4 plant, which makes it very competitive with C3 plants over summer and gives it tolerance to the triazine herbicides.

Reproduction:

By seed.

Flowering times:

December to May in SA.
Summer to autumn in NSW.
December to May in Perth.

Seed Biology and Germination:

Vegetative Propagules:

Hybrids:

D. sanguinalis ssp. pectiniformis has stiff hairs on the margins of the lower lemma.

Allelopathy:

Population Dynamics and Dispersal:

Origin and History:

Southern Europe, Mediterranean, Asia and America. Widespread in warm and temperate areas of the world.

Distribution:

ACT, NSW, NT, QLD, SA, VIC, WA.
Lord Howe Island.

Courtesy Australia's Virtual Herbarium.

Habitats:

Summer moist areas, irrigated areas.

Climate:

Temperate to sub tropical.

Soil:

Prefers summer moist soils.

Plant Associations:

Significance:

Beneficial:

Eaten by stock, but little forage value.

Detrimental:

Serious weed of pineapples, orchards and vegetables.
Weed of cultivation, irrigated lucerne, rice, vegetables, vineyards, orchards, rotational crops, gardens, lawns, recreational and disturbed areas.

Toxicity:

Not recorded as toxic.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Herbicide resistance:

Biological Control:

Related plants:

Cotton Panic grass (Digitaria brownii)
Curly Umbrella grass (Digitaria hystrichoides)
Finger Panic grass (Digitaria coenicola)
Queensland Blue Couch (Digitaria didactyla)
Silky Umbrella grass (Digitaria ammophila)
Small Flowered Finger grass (Digitaria parviflora)
Smooth Summer grass (Digitaria ischaemum)
Summer grass (Digitaria ciliaris) is very similar.
Tufted Umbrella grass (Digitaria hubbardii)
Umbrella grass (Digitaria divaricatissima)
Woolly Finger grass (Digitaria eriantha)

Plants of similar appearance:

Summer grass (Digitaria ciliaris) is almost identical. Distinguished on flower characters. In summer grass the upper glume is 50-75% as long as lemma and the lower lemma is silky hairy, whilst in Crabgrass the upper glume is 30-50% as long as lemma and the lower lemma is rough to touch. In Summer grass the nerves on the upper lemma are scabrous at least in the upper part whereas in Crabgrass the are not.
Crowsfoot grass (Eleusine indica) is similar but has hairless leaves, doesn't root at the nodes, has fewer flower heads and more than 2 florets per spikelet.
Paspalum, Carpet grass, Barnyard grass, Millet, Pigeon grass, Kikuyu are similar.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P43-44.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P218. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P63-65.

Ciba Geigy (1980) Grass Weeds 1. CIBA GEIGY Ltd, Basle, Switzerland. P49. Diagrams.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P86.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P52-53. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). 437.3.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P955.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.