Swainsonpea or Austrian Peaweed [Sphaerophysa salsula (Pall.)
DC.][SWASA][CDFA list: A] Photographs Map
long-lived perennial with aggressive creeping roots, to 1.5 m tall.
Swainsonpea is potentially noxious wherever alfalfa [Medicago sativa
L.] is grown for seed. A close resemblance of the two seeds makes it difficult
to separate in seed production systems. Introduced from Asia.
vigorous than alfalfa seedlings.
erect to ascending, covered with short white hairs. Leaves compound, odd-pinnate.
Leaflets 15-23, oblong to ovate, 0.5-2 cm long. Lower surfaces of leaflets
covered with short white hairs; upper surfaces mostly glabrous. Stipules awl-like,
mostly 0.5 cm long or less, fused at the base.
and UNDERGROUND STRUCTURES:Develops
an extensive system of robust, woody, creeping lateral roots that
produce new shoots. Roots can associate with nitrogen fixing bacteria.
Pea-like, on racemes in the leaf axils near the stem tips. Corollas brick-
to orange-red, 12-14 mm long. Stigmas finely hairy. Pedicels 3-7
inflated at maturity, ovoid to spherical, grooved on top,1.5-3.5 cm
long, with a stalk-like base 4-7 mm long that protrudes beyond the persistent
calyx tube, glabrous, membranous to papery, translucent, often mottled. Pods
do not release seeds (indehiscent). Seeds several to numerous, flattened,
semi-circular to triangular with a slight notch, ~ 2 mm long, smooth, dull
dark brown to black.
sites, roadsides, irrigation ditches, cultivated crops.
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Southern San Joaquin Valley (ce Kings, c Kern cos.). To 500 m (1650 ft).
PROPAGATION/PHENOLOGY:Reproduces by seed
and vegetatively from creeping roots. Entire pods disperse as units
with seeds enclosed. A large proportion of seed is hard-coated and requires
scarification to germinate.
weedy perennial members of the pea family that can superficially resemble
swainsonpea include camelthorn [Alhagi pseudalhagi (M.Bieb.)
Desv.] and wild licorice [Glycyrrhiza lepidota Pursh.]. Unlike
swainsonpea, camelthorn has thorns, simple leaves, and
pods not inflated. Wild licorice has yellowish- to greenish-white
flowers, gland-dotted leaves, and bur-like fruits covered with
hooked prickles. In addition, many native locoweeds [Astragalus
spp.] have leaves and inflated pods that closely resemble those of swainsonpea.
However, locoweeds have glabrous
stigmas and styles, pods that lack the stalk-like base above the calyx,
and most do not have red flowers. Only scarlet milkvetch [Astragalus
coccineus Brandegee] has red flowers. Scarlet milkvetch is a desirable
native species that occurs only on the western edge of the deserts and east
of the Sierra Nevada in sagebrush communities or pinyon woodlands.
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Prevention and control: Swainsonpea
is a long-lived perennial legume found throughout the western United States.
It may have been introduced to the United States from Asia for forage or soil
stabilization. In California, it has been detected in Kern and Kings counties
and is limited in its distribution. Swainsonpea is a threat to alfalfa seed
producers; its seeds are nearly identical in size, shape, and weight to alfalfa
seed, making separation almost impossible. Avoid introducing swainsonpea by
using only certified alfalfa seed.
There is little information regarding control of swainsonpea. Tillage may
be ineffective due to an extensive creeping root system that sends up numerous
shoots, and may spread severed rootstocks to new areas. Tillage equipment
should be thoroughly cleaned after working in infested areas.
Mowing or grazing may reduce seed production, but will be ineffective for
complete control. Cattle likely prefer the seed pods of swainsonpea, and seed
viability probably remains high after passing through animals. Therefore,
cattle should be removed from areas after seed production. Like many other
legumes, the seeds are extremely hard and may be viable in the soil for many
There is no information regarding chemical control of swainsonpea. Herbicides
such as glyphosate, clopyralid, triclopyr, dicamba, 2,4-D, and picloram may
be effective in noncrop areas. Control in alfalfa may be difficult, but glyphosate
applied with a rope-wick applicator may be effective. However, regrowth is
likely with any of these treatments and reapplication may be necessary. Optimal
time for treatment is unknown, but other perennial weeds may be most susceptible
either at early bloom or during the fall when translocation of carbohydrates
to the roots is maximized.
Alfalfa is generally more competitive than swainsonpea. Therefore, maintaining
a healthy competitive stand may reduce the potential for invasion. Swainsonpea
may be favored in older, thinning stands of alfalfa. Serious infestations
in alfalfa may require rotating to a grass crop where more effective control
options are available.
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