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. 2016^Footnote 1).

Worldwide: The genus contains about 250 species originating from tropical and warm temperate parts of the world (Mabberley 2008^Footnote 2). It includes cultivated and weedy species, some widely introduced around the world (USDA-ARS 2016^Footnote 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 2003^Footnote 4, CABI 2016^Footnote 5). Weedy species infest a variety of crops worldwide and are problematic in lawns (CABI 2016^Footnote 5).

General Information

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

Crabgrasses are problem weeds in sandy and loam soils (Darbyshire 2003^Footnote 4, CABI 2016^Footnote 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 2016^Footnote 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