terrestris L.][TRBTE][CDFA list: C] Photographs
ground burnut, puncture weed, bullhead, goathead, Mexican sandbur
DESCRIPTION:Noxious summer annual,
with prostrate stems up to 2.4 m long. Plants produce many
stout-spined burrs that can injure people and animals and puncture
bicycle tires. Foliage is toxic to livestock, especially
sheep, when consumed in quantity. Fruits are used medicinally
in India. Introduced from the Mediterranean region. Once one of
Californias most troublesome weeds, puncturevine
is currently controlled by the stem weevil (Microlarinus lypriformis)
and seed weevil (M. lareynii), introduced from Italy as
biocontrol agents in 1961.
Cotyledons oblong, 4-15 mm long, thick, creased down the
center, slightly indented at the tips. First and subsequent
leaves resemble those of mature plants.
highly branched, green to reddish-brown, prostrate and
spreading radially from the crown on open ground
to +/- erect when shaded or competing with other plants. Foliage
often sparse to moderately covered with silky and/or bristly silver
hairs. Leaves opposite, even-pinnate compound, ~
3-5 cm long, with 3-7 leaflet pairs per leaf and a small
extension at the tip. Leaflets oblong, 5-15 mm long, with +/-
oblique bases. Stipules leaf-like. Photosynthesis is by the C4
and UNDERGROUND STRUCTURES:Taproot deep (to 2.6 m), slender, branched, often
somewhat woody, with a network of numerous fine rootlets. Roots
can develop nitrogen-fixing nodules.
Flowers axillary, solitary, bright yellow,
5-15 mm in diameter. Petals and sepals 5(4), deciduous.
Stamens and ovary chambers twice the number of petals. Insect-pollinated.
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and SEEDS:Woody burrs gray to
yellowish-tan, hairy, to ~ 1 cm in diameter, +/- flattened, lobed,
separate into 5(4) wedge-shaped nutlets, each
with 2 stout spines 4-7 mm long and several prickles.
Seeds usually 3-5 per nutlet, remain enclosed within burrs.
CHARACTERISTICS:Burrs often remain on senesced plants or the soil
roadsides, railways, cultivated fields, yards, waste places, walk
ways. Grows best on dry sandy soils, but tolerates most soil types.
Intolerant of freezing temperatures.
California, to 1000 m (3300 ft); to Wyoming, Eastern U.S., Central
Mexico. Nearly worldwide. Prevalent in areas with hot summers
and dry soils.
by seed. Nutlets disperse by adhering
to tires, shoes and clothing of people, fur, feathers, and feet
of animals. Most newly matured seeds are dormant and require an
afterripening period of ~ 6 months to 1 year. Germination requires
warm temperatures. The largest seed in a nutlet is usually the
first to germinate. Other seeds may germinate or remain dormant
depending on moisture availability. Buried seed can remain viable
for several years. Seedlings emerge early spring through summer,
often in flushes following increased soil moisture. On sandy soils,
seedlings emerge from depths to ~ 5 cm (less on heavy soils).
Seedlings develop a deep root system in a few weeks, and flowers
may be produced within 3 weeks, burrs within 6 weeks. Plants typically
bear numerous burrs (average 200-5000) until the cool season commences.
In tropical regions, plants develop woody roots and become perennial.
FAVORING/DISCOURAGING SURVIVAL:Removal of plants with burrs and repeated cultivation
to prevent burr formation or planting competitive vegetation can
help control infestations.
SIMILAR SPECIES:Puncturevine is unlikely to be confused
with other weeds.
Mechanical: Tillage following germination and emergence
is effective. However, tillage may bury seed that remain viable in the soil
for several years. Hand-pulling is feasible for small infestations and is easiest
when soils are moist and the vines are long enough to grasp. Mowing is ineffective
due to the prostrate growth habit of the plant.
Biological: There are two species of weevils which are being used to control
puncturevine. The stem boring weevil, Microlarinus lareynii and the fruit boring
weevil Microlarinus lypriformis. The insect larvae attack the seeds and stems
and have given good puncturevine control. Both insects are available in California
Chemical: Chlorosulfuron, 2,4-D, imazapyr, MCPA, paraquat, glyphosate, and dicamba
are effective on puncturevine. Consult the label for proper rate and timing.
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