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Carelessweeds are annual weedy herbs belonging to the amaranth
family. Texas has 23 recorded species, which vary in growth
forms from prostrate to branching upright. Carelessweed is often
called pigweed because swine relish it. It bears inconspicuous
flowers from June to November.
Distribution and habitat
Carelessweed abounds on disturbed sites especially in barnyards
with rich, moist soils throughout most of the United States.
It is also a common weed in croplands.
Regions: 2, 3,
4, 5,
6, 7,
8, 9,
10 .
Toxic agent
Carelessweeds can accumulate nitrates from the soil to toxic
levels. Environmental factors often influence nitrate accumulation.
For example, nitrate poisoning is more likely to occur if
the plant is growing in soils high in nitrogen, especially
during drought. Plants containing more than 1 percent nitrate
are dangerous. The plant is also known to cause bloat. All
ruminants are susceptible to nitrate poisoning.
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Livestock
signs
Animals with acute nitrate poisoning are often found dead with
no previous history of illness. Less acute nitrate poisoning
signs often occur in this order:
Weakness
Unsteady gait
Collapse
Shallow and rapid breathing
Rapid pulse
Dilated pupils
Delayed abortion
Coma
Death
Blood may appear chocolate brown at time
of death.
Pregnant animals surviving acute nitrate poisoning may abort
3 to 5 days later.
Integrated management strategies
Many livestock relish carelessweed, particularly in its
early growth stages. Although it is usually most dangerous
during drought, poisonings have occurred at all growth stages
and under a variety of conditions. The nitrate content of
carelessweeds is significantly higher in the morning than
in the afternoon. Keep livestock off heavily infested pastures
during early stages of plant growth and after sudden temperature
changes. This plant remains dangerous in hay or silage.
Because livestock are most often poisoned when they are
placed in a pen containing many carelessweed plants, focus
herbicide or mechanical treatments on these areas. The plants
nitrate content may increase immediately after herbicide
(especially 2,4-D) treatment; thus, keep livestock away
until the plants have dried completely.
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