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Flower
Pod |
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Garboncillo, Rattleweed
(Astragalus wootonii)
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Description
Garboncillo is a much-branched, annual
legume with erect, hairy stems that vary from about 3 to 12
inches long. The leaves are composed of 9 to 19 leaflets that
are hairy beneath and smooth above. Flowers are pink or purplish
to white in color. The most conspicuous part of the plant
is the fruit, which is a large, one-celled, inflated pod.
Distribution and Habitat
In Texas, garboncillo is generally
restricted to the Trans-Pecos region. It is also common in
southern New Mexico, eastern Arizona and northern Mexico.
Garboncillo is most abundant in valleys that accumulate runoff
water from the surrounding hills, as well as in bar ditches,
along trails and around earthen tanks.
Regions: 9, 10.
Toxic Agent
The toxic principle is an alkaloid
called swainsonine. Horses are particularly susceptible to
garboncillo, although cattle, sheep, and goats may also develop
garboncillo poisoning. It is estimated that symptoms of poisoning
are first produced in cattle after they have consumed about
90 percent of their body weight of the plant. As much as 200
to 350 percent of their body weight of the plant, eaten over
a period of several months, may be required to kill cattle,
sheep and goats. However, about 30 percent of body weight
consumption will produce signs in a horse, and about 75 percent
may be fatal. Both dry and green garboncillo is toxic. The
dead stems remaining following die-back at frost are readily
consumed by livestock.
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Livestock Symptoms
Symptoms develop from the
involvement of sensory and motor functions. In cattle, general
symptoms observed include:
- carrying the head a little lower than
normal
- a vacant stare, perhaps due to distorted
vision
- trembling of the head and difficulty
or inability to eat and drink
- abortion
Swainsonine is also passed
in the milk of cows, possibly explaining the unthriftiness
of some suckling calves. Symptoms for sheep are much the
same, while goats will develop an ascending paralysis
which becomes increasingly severe, eventually involving
the forelegs.
In horses, the time between onset of symptoms
and death is much shorter than in cattle. The horse will
be listless and will not notice ordinary activities, but
on being stimulated by some sudden event, will become excessively
excited and wild, even to the point of inflicting fatal
injury to themselves. Other symptoms are similar to those
for other species of livestock. Horses with chronic locoism
rarely recover and are dangerous for riding because of unpredictable
and permanent behavioral changes.
Integrated Management Strategies
Since garboncillo is an annual, mechanical removal
of the plant around tanks, along roadways and in other hazardous
sites is often effective. Proper stocking rates and grazing
management practices can help reduce consumption of garboncillo.
Sound range management practices such as these ensure the
maintenance of good to excellent range condition, and are
the best prevention against garboncillo poisoning. As range
condition improves, so does plant diversity. When more desirable
forage is available, animals are much less likely to eat
garboncillo. Livestock also should receive proper supplementation
of energy, protein, minerals and vitamins.
Herbicide spot or broadcast applications
can be used successfully if benefits outweigh the cost.
Individual plant treatments with Grazon P+D®
(mix 2 gallons with 1 to 2 quarts surfactant and water to
make 100 gallons) applied directly to the leaves of the
plant may be effective in controlling small problem areas.
When a large area is infested, aerial or ground broadcast
applications of 0.94 pounds a.i./acre of Grazon P+D®
(3 pints) have given good results.
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