Bur bristlegrass (Setaria verticillata)

Introduction:

Setaria verticillata is a native European grass, invading agricultural, urban, and other disturbed areas throughout North America, Central America, South America Africa, Asia, and the North and South Pacific. A problematic crop weed S. verticillata, has inflicted considerable environmental and economic costs, is known to adapt to local conditions rapidly, and has developed resistance to atrazine and other C 1/5 herbicides.

Description:

Setaria verticillata is a loosely tufted, annual grass. Its culms reach 10–100 cm high or more, geniculately ascending. Leaf-blades broadly linear, 5–30 cm long, 4–16 mm wide, flaccid, glabrous to loosely pilose; sheaths glabrous to pubescent. Panicle spiciform, linear to untidily lobed, 2–15 cm long, often entangled, the rhachis hispidulous; bristles 3–8 mm long, retrorsely barbed, tenaciously clinging. Spikelets ellipsoid, 1.5–2.5 mm long; lower glume 1/3–1/2, the upper as long as the spikelet; lower floret sterile, the palea minute; upper lemma finely rugose.

Occurs in:

Agricultural areas, coastland, urban areas.

Habitat description:

Setaria verticillata generally occurs in temperate to tropical climates, altitudes 0-2200 m, and agricultural or other disturbed locations. It has been reported to prefer shady damp sites, but is rarely found in wetlands generally.

General impacts:

Setaria verticillata is problematic, cosmopolitan crop weed. It has the ability to adapt to a wide range of habitats enabling widespread infestation in temperate, disturbed areas throughout the world. It exhibits phenotypic plasticity and is quite resilient to a number of conditions being resistant to several herbicides, mechanical damage, and

drought. Its invasive nature has resulted in significant damage to corn crops and the displacement of native grasses.

Notes:

Some authorities recognize Setaria verticillata and Setaria adhaerens as one species while others recognize them as two. The more temperate S. verticillata has ciliate sheath-margins, glabrous blades and spikelets over 2 mm long. The more tropical S. adhaerens has glabrous sheath-margins, hairy blades and spikelets under 2 mm long. However, these are only two among a number of intergrading populations, and some recommend treating the whole complex as a single polymorphic species.

Geographical range:

Native range: Europe: France, Germany, Italy, Portugal, Spain, United Kingdom.

Known introduced range: Australia, Canada, Chile, China, Federated States of Micronesia (FSM), French Polynesia, Guam, Guatemala, Hawaii, Indonesia, Israel, Johnston Atoll, Kenya, Kiribati, Marshall Islands, Mauritius, Mexico, Midway Islands, Nambia, New Zealand, Norfolk Island, Palestine Territory, Peru, Pitcairn, South Africa, Tasmania, Thailand, Uganda, United Republic of Tanzania, United States, Wake Island.

Local dispersal methods:

On animals: Setaria verticillata bears fruits with retrorsely barbed bristles that cling to animals and are distributed by them.

On clothing/footwear:Setaria verticillata may be distributed by people via their clothing and footwear as it bears fruits with retrorsely barbed bristles that cling to them.

Management information:

Chemical: Setaria verticillata was found to develop resistance to Photosystem II inhibitors, or C 1/5 herbicides when it became resistant to field levels of atrazine treatment in one study . Its rates of recovery of net CO2 mg per dm2 per h/h following a treatment of atrazine, cyanazine, and cyprazine at 1.16×10 -5 M leached through silica sand media were 1.5, 0.5, and 0.3 CO2 mg per dm2 respectively.

Reproduction:

Setaria verticillata is a self pollinated annual which forms long-lived, heterogeneous seed pools in the soil resulting from a dormant seed rain. In soil seed pools, after-ripening, the occurrence and timing of seedling emergence, and the induction of secondary, summer dormancy are regulated by seasonally and diurnally varying soil oxygen, water, and temperature signals. This precise and adaptable seed emergence contributes greatly to S. verticillata’s success in disturbed areas. It is known to have a considerably low intrapopulation genetic diversity and huge genetic diversity between populations compared to similar plant species.