Weed Seed: Panicum spp. (Panic grass)

Family

Poaceae

Common Name

Panic grass

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 6 species found in Canada, distributed across Canada with the exception of NL, NU and YT (Brouillet et al. 2016Footnote 1).

Worldwide: Panicum is a large genus of 300 to 600 species originating from tropical and warm temperate parts of the world (Mabberley 2008Footnote 2, eFloras 2016Footnote 3). Its numbers are difficult to estimate because its limits are not clear (Barkworth et al. 2003Footnote 4). Panicum includes a number of weedy species as well as species cultivated as fodders, grains and ornamentals (Mabberley 2008Footnote 2).

Duration of life cycle

Most are annual species

Seed or fruit type

Floret

Identification features

Size

  • Florets of Panicum spp. are generally smaller than most Poaceae genera
  • Florets of weed Panicum spp. vary from 1.5 - 2.5 mm long; crop Panicum spp. vary from 2.5 - 3.5 mm long

Shape

  • Florets of Panicum spp. are oval-shaped, not elongate as other genera

Surface Texture

  • Florets of Panicum spp. have a smooth and glossy surface
  • The florets are hardened and shell-like, not leathery or papery as other Poaceae genera

Colour

  • Florets of weed Panicum spp. are greenish-brown with, pale ends and several pale, longitudinal lines on lemma
  • Florets of crop Panicum spp. are solid straw-yellow or orange

Other Features

  • Callus at base of floret is bow-shaped and can be straw yellow, brown or black
  • Panicum spp. florets do not have rachillas or pedicels, and the palea lacks conspicuous teeth
  • Panicum spp. may be found as spikelets; the glumes cover the floret and are papery, straw yellow with raised lines

Habitat and Crop Association

Cultivated fields, old fields, pastures, prairies, shores, floodplains, marshes, swamps, ditches, shallow water, dunes, forest edges, forest clearings, open forests, orchards, vineyards, roadsides, railway lines and disturbed areas (Barkworth et al. 2003Footnote 4, Darbyshire 2003Footnote 5, DiTomaso and Healy 2007Footnote 6). Witch grass (Panicum capillare) commonly infests corn, soybeans, winter wheat and sorghum, and can also infest grasslands (Clements et al. 2004Footnote 7).

General Information

Of the six species occurring in Canada, four are native and two are introduced (Brouillet et al. 2016Footnote 1). Most species occur as weeds of agricultural habitats (Darbyshire 2003Footnote 5, Clements et al. 2004Footnote 7). Witch grass (Panicum capillare), a native species, is the most commonly found in cultivated fields and gardens (Frankton and Mulligan 1993Footnote 8).

Switch grass (Panicum virgatum) and proso millet (Panicum miliaceum) are cultivated for seed and forage, and the latter has a weedy form that is common and competitive in corn fields in Canada (Royer and Dickinson 1999Footnote 9, Darbyshire 2003Footnote 5).

Similar species

Genera from the same tribe as Panicum spp., Paniceae, have features that distinguish them from other grass tribes such as:

  • 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, Panicum spp. can be distinguished by:

  • Smooth, glossy floret surface
  • Bow-shaped callus
  • Several pale, longitudinal lines on the lemma of weed Panicum spp.

Photos

Blue panic grass (Panicum antidotale) floret
Blue panic grass (Panicum antidotale) florets
Witch grass (Panicum capillare) florets and spikelet
Witch grass (Panicum capillare) floret, lemma view
Witch grass (Panicum capillare) floret, palea view
Witch grass (Panicum capillare) spikelet (L) and florets (R)
Fall panic grass (Panicum dichotomiflorum) spikelet (L) and floret (R)
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