Annual bursage [Ambrosia acanthicarpa Hook.][FRSAC] Photographs

Giant ragweed [Ambrosia trifida L][AMBTR][CDFA list: B] Photographs Map of Distribution

SYNONYMS:

• annual bursage: annual burweed, sand-bur, Franseria acanthicarpa Hook., Franseria palmeri Rydb., Franseria montana Nutt., Franseria californica Gand., Gaertneria acanthicarpa Britt.
• giant ragweed: great ragweed, kinghead, tall ragweed, buffaloweed

GENERAL DESCRIPTION:Erect summer annuals that typically colonize disturbed open sites. Pollen of Ambrosia species is a major cause of allergies in the summer/fall months.

• annual bursage: To 1.5 m tall. Widespread native. Inhabits many natural plant communities and is not considered a pest under most circumstances. However, it can become problematic in agricultural fields, forestry regeneration sites, and disturbed areas.
• giant ragweed: Typically to 2 m tall, rarely to 6 m in moist fertile soils. Infestations can be noxious, but seldom persist in California. Introduced from the Central and Eastern U.S., where it is often troublesome in agricultural fields and drainage areas.

SEEDLINGS:

• annual bursage: Cotyledons oblong to elliptic (~ 0.6-1.4 cm long). Subsequent leaves deeply pinnate-lobed, sparsely covered with short, white or gray, bristly hairs.
• giant ragweed: Cotyledons round, ovate, or oblong, thick, sometimes slightly indented at the tips, ~ 2-4 cm long, 1-1.6 cm wide. First leaves ovate to lanceolate, slightly coarse-lobed. Subsequent leaves opposite, coarsely 3-lobed. First and subsequent leaves moderately covered with stiff hairs.
  
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MATURE PLANT:

• annual bursage: Foliage covered with white to gray, short, bristly hairs. Leaves often opposite near the stem bases, alternate on the upper stems, gray-green, bipinnately lobed, with the primary lobes deep, to 8 cm long and 7 cm wide.
• giant ragweed:Stems coarse, single or branched, woody at the base, longitudinally black-lined, covered with soft to bristly hairs. Leaves opposite, broad, palmately 3- to 5-lobed, 6-35 cm long, sparsely covered with minute, stiff hairs. Margins finely serrate.

ROOTS and UNDERGROUND STRUCTURES:Taproot short, thin, with many fibrous roots.

FLOWERS:Heads small, greenish, composed of staminate (male) or pistillate (female) disc flowers. Staminate and pistillate heads are separate on a single plant (monoecious). Terminal spikes consist of nodding staminate heads, 2-5 mm in diameter. Pistillate heads are clustered in the leaf axils below the spikes. Staminate head phyllaries fused, cup-like, with 3 longest lobes blackish along the midveins. Pistillate head phyllaries fused, persistent, enclose a single ovary, become a bur in fruit. Wind-pollinated.

• annual bursage: August-November.
• giant ragweed: June-September.

FRUITS and SEEDS:Hardened phyllaries tightly enclose a single achene to form a bur. Burs +/- obovoid.

• annual bursage: Burs highly variable, often golden brown. Bur body 4-8 mm long, typically with 6-30 sharp-pointed, flattened, straight spines 2-5 mm long.
• giant ragweed: Burs 6-12 mm long, stoutly blunt-beaked at the apex, brown to gray. Beak surrounded by a crown of 5-8 short, thick blunt teeth of vestigial spines terminating each rib. Most seed matures August-October.
  

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POSTSENESCENCE CHARACTERISTICS:Rigid stems with fruits can persist into the winter months.

HABITAT:

• annual bursage: Dry slopes, sandy flats and alluvial plains, grasslands, foothill woodlands, coastal sage scrub, disturbed sites, agricultural fields, forestry sites. Comonly grows on dry or moist sandy soils.
• giant ragweed: Disturbed sites, agricultural fields, roadsides, drainage areas. Grows best on fertile, moist soils.

DISTRIBUTION:

• annual bursage: North Coast Ranges, Sierra Nevada, Southwestern region, Mojave and Sonoran deserts, Great Basin; to Washington, Montana, Wyoming, Texas, New Mexico. To 2200 m (7200 ft).
• giant ragweed: Uncommon. San Joaquin Valley (especially San Joaquin, Contra Costa, Madera cos.), Central Coast (especially Monterey Co.), South Coast region (especially Orange Co.), Modoc Plateau (Lassen Co.). To 100 m (330 ft).

PROPAGATION/PHENOLOGY:Reproduces by seed.

• annual bursage: Burs disperse by clinging to agricultural machinery, the shoes, clothing and the feet, fur or feathers of animals. The biology of this species is poorly understood.
• giant ragweed: Most burs fall near the parent plant, but some can diperse long distances with water, animals, and human activities. Burs are rarely consumed by animals. An average size plant produces roughly 275 seeds. Newly matured seed is usually dormant and requires a cold, moist period to germinate. Seeds typically germinate at temperatures between 8-41º C (46-106ºF), optimum 10-24 º C (50-75º F). Most germination in the field occurs early to mid-spring and at soil depths to 16 cm, optimal 2 cm. Germination rarely occurs on the soil surface. Seedlings emerging from shallow depths are most likely to survive. Plants effectively compete other species for light.
  

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MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:giant ragweed cut in mid- to late summer can still recover and produce seed. Cultivation to prevent seed production can help control infestations.

SIMILAR SPECIES:

• Western ragweed [Ambrosia psilostachya D.C.][AMBPS] is a widespread erect, native perennial that is sometimes weedy in orchards and vineyards. Its foliage is similar to that of annual bursage, but its burs are shaped like those of giant ragweed. Unlike annual bursage and giant ragweed, western ragweed can reproduce vegetatively from creeping roots and leaves are mostly 1-pinnatem divided, with irregularly toothed margins. Western ragweed commonly inhabits roadsides and dry fields throughout California (except some regions in the Mojave Desert and Great Basin) and most of the Western U.S. to 1000 m (3280 ft). Flowers July-November.
• Common ragweed [Ambrosia artemisiifolia L.][AMBEL] is an annual introduced from the Eastern U.S. that closely resembles annual bursage. It is not as common in California as it is in the Mid-western and Eastern U.S. Common ragweed is most easily distinguished by having staminate flower heads with green phyllaries that lack a black midvein and burs similar to those of giant ragweed, but considerably smaller (2-4 mm long). It inhabits disturbed sites in Northwestern California, eastern Sacramento Valley, South Coast, and low regions of the Eastern Sierra Nevada, to 650 m (2100 ft).

CONTROL METHODS:

Prevention: Giant ragweed is extremely competitive and is very difficult to control in many broadleaf crops. While relatively uncommon in California, it is important to prevent giant ragweed from increasing due to its competitive ability and important role as a human allergen.
One of the primary mechanisms of spread in crop areas is by harvesting equipment.

Mechanical: Tillage is effective for control of seedlings because of their early emergence in relation to many other summer annual weeds. Tillage becomes less effective as plants become larger. Under moist soil conditions, plants may be "transplanted" and begin growing in another area. Repeated mowing will effectively reduce seed production but will not eliminate giant ragweed.

Chemical: Populations of giant ragweed in other states have been found to be resistant to ALS herbicides. Pre-emergent herbicides include bromacil, prometrone, and tebuthiurun for non crop applications. Post-emergence herbicides which provide good control for giant ragweed are glyphosate, dicamba, and 2,4-D. Broadcast applications of glyphosate at 2.0 pt/A will control plants up to six inches in height. Tank mixing 2,4-D at 1 pint/A with glyphosate will also provide giant ragweed control. Imazethapyr is also recommended for post emergence control of giant ragweed.

References:
Abul-Fatih, H.A. and F. A. Bazzaz1980. The biology of Ambrosia trifida L. IV. Demography of plants and leaves. New Phytologist 84 (1):107-111.
Abul-Fatih, H. A., F. A. Bazzaz, and R. Hunt. 1979. The biology of Ambrosia trifida L. III. Growth and biomass allocation. New Phytologist 83 (3):829-838.
Abul-Fatih, H. A. and F. A. Bazzaz. 1979. The biology of Ambrosia trifida L. II. Germination, emergence, growth and survival. New Phytologist 83 (3):817-827.
Ballard, T. O., M. E. Foley, and T. T. Bauman 1996. Response of common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida) to postemergence imazethapyr. Weed Science 44 (2):248-251.
Bassett, I. J. and W. C. Crompton. 1982. The biology of Canadian weeds. 55. Ambrosia trifida L. Canadian Journal of Plant Science 63:1003-1010.
Buhler, D. D.1997. Effects of tillage and light environment on emergence of 13 annual weeds.
Weed technology 11 (3):496-501.
Franey, R. J. and S. E. Hart. 1999. Time of application of cloransulam for giant ragweed (Ambrosia trifida) control in soybean (Glycine max). Weed Technology 13 (4):825-828.
Hartnett, D. C., B. B. Hartnett, and F. A. Bazzaz. 1987. Persistence of Ambrosia trifida populations in old fields and responses to successional changes. American Journal of Botany 74 (8):1239-1248.

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