HITS since April 5, 2000
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Leaf
Flower |
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Bishop’s-Weed, Greater
Ammi
(Ammi majus)
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Bishop’s-weed is a showy, cool-season annual
up to 3 feet tall. The oblong leaves may be up to 8 inches long
and 5.5 inches wide. The many white flowers are arrayed in an
umbrella shape up to 3 inches across located at branch tips.
Each flower gives rise to a small, oblong, rough fruit.
Distribution and habitat
This plant was introduced from the Mediterranean region and
has been widely disseminated in the Western Hemisphere. It
is found in east and south Texas, usually along roadsides,
as it has apparently been included in some wildflower seed
mixes. In the past 15 years, bishop’s-weed has become more
widespread, and is now established in some roadside pastures.
It is likely to spread further in coming years, posing a greater
threat to livestock.
Regions: 1, 2,
3, 4,
6, 7.
Toxic agent
Bishop’s-weed contains a furocoumarin in all parts of the
plant, but it is especially concentrated in the seed. The
compound is photoactive, causing primary photosensitization
in cattle, sheep and birds. All animals consuming the seed
should be considered at risk.
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Livestock
signs
Signs in affected animals:
• Increased body temperature
• Photophobia (the animals shy away from
light)
• Edema of the muzzle, ears, udder, scrotum
and vulva
• Sunburn of light-colored skin
• Inflammation of skin
Thin-skinned areas and those having thin or no hair are often
those most affected. Inflammation is followed by swelling,
blisters, fluid seepage and sometimes sloughing of the skin.
In dark animals, the skin is not blistered or sloughed, but
may become painful and thickened, with crusted hair.
Integrated management strategies
Primary photosensitization does not usually result in death.
Some animals become severely scarred, and growth of young
calves can be stunted because the cows will not let them
nurse. Provide adequate water and feed in shade to prevent
further sunburn. Check pastures next to roads with bishop’s-weed
for flowering plants, which should be removed before seeds
form.
  
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Send Comments to: Dr.
Charles Hart, Dr. Bruce Carpenter,
Dr. John Reagor , or Dr.
Allan McGinty.
This material is based upon work supported by the Cooperative
State Research, Education, and Extension Service, U.S. Department of Agriculture,
under a Southern Region IPM Program special project number 97-EPMP-1-0153.
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