Weed Seed: Digitaria spp. (Crabgrass)

Family

Poaceae

Common Name

Crabgrass

Regulation

Secondary Noxious, Class 4 and Noxious, Class 5 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: The genus includes 3 species found in Canada, distributed across Canada with the exception of NL and the territories (Brouillet et al. 2016Footnote 1).

Worldwide: The genus contains about 250 species originating from tropical and warm temperate parts of the world (Mabberley 2008Footnote 2). It includes cultivated and weedy species, some widely introduced around the world (USDA-ARS 2016Footnote 3).

Duration of life cycle

Most species annual; some perennial

Seed or fruit type

Spikelet

Identification features

Size

  • Digitaria spp. spikelets vary in size; generally smaller than most Poaceae genera
  • Spikelets of commonly encountered Digitaria spp., such as D. sanguinalis and D. ischaemum are 2.0 - 4.0 mm long

Shape

  • Digitaria spp. spikelets are short or long oval-shaped ; pointed at the top

Surface Texture

  • Digitaria spp. spikelet glumes are papery and hairy
  • Florets leathery and pitted in longitudinal lines

Colour

  • Spikelet glumes straw-yellow
  • Florets generally brown or greenish-brown;  some species black

Other Features

  • Long oval-shaped Digitaria spp. spikelets have a distinctive pointed glume partially covering the lemma
  • In short oval-shaped Digitaria spp. spikelets, the glume covers the entire lemma
  • Digitaria spp. florets do not have rachillas or pedicels, conspicuous palea teeth or a distinct callus

Habitat and Crop Association

Cultivated fields, pastures, gardens, lawns, orchards, vineyards, shores, roadsides, railway lines and disturbed areas (Darbyshire 2003Footnote 4, CABI 2016Footnote 5). Weedy species infest a variety of crops worldwide and are problematic in lawns (CABI 2016Footnote 5).

General Information

The three species occurring in Canada are: large crabgrass (Digitaria sanguinalis), smooth crabgrass (D. ischaemum) and fall crabgrass (D. cognata) (Darbyshire 2003Footnote 4, Brouillet et al. 2016Footnote 1). The first two have been introduced into Canada and the third is native (Darbyshire 2003Footnote 4).

Crabgrasses are problem weeds in sandy and loam soils (Darbyshire 2003Footnote 4, CABI 2016Footnote 5). Large crabgrass plants can produce approximately 150,000 seeds in a growing season and mature plants spread over large areas by tillering soon after establishment (CABI 2016Footnote 5).

Similar species

Genera from the same tribe as Digitaria spp., Paniceae, have certain features that distinguish them from other tribes in the Poaceae:

  • Shed as a spikelet
  • Spikelets have papery, unequal glumes, a papery sterile floret and a hard, shell-like or leathery fertile floret
  • Florets lack a rachilla or pedicels
  • Inconspicuous palea teeth
  • Florets tend to be short oval rather than elongate

Within the Paniceae tribe, Digitaria spp. have distinguishing features:

  • Pointed glume partially covering the lemma in some species
  • Leathery florets with a pitted surface
  • Florets are black in some species
  • Indistinct callus

Photos

Southern crabgrass (Digitaria ciliaris) spikelets
Smooth crabgrass (Digitaria ischaemum) spikelets
Large crabgrass (Digitaria sanguinalis) spikelets
Large crabgrass (Digitaria sanguinalis) spikelet, outer side
Large crabgrass (Digitaria sanguinalis) spikelets, inner side
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