POISONOUS AND INJURIOUS PLANTS ta 
is a nuisance because it occupies large areas where desirable forage 
species could be grown. 
Toxiciry AND Symproms.—Thistleroot seeds contain two poisonous 
alkaloids, beberine and protopine (52). Chick-feeding trials show 
the leaves and roots are also poisonous. However, because of its un- 
pleasant taste and its prickles, animals seldom eat the plant and cases 
of livestock poisoning are very rare. 
MANAGEMENT AND Controu.—Control of this pest is difficult because 
it seeds so copiously. Ordinary cultivation practices kill plants in 
the seedling stage. Both mechanical and chemical control measures 
are effective. The stand may be reduced by mowing before the seeds 
are mature. Ester forms of 2.4-D and 2,4.5-T kill the plant. For 
complete eradication it is necessary to repeat the treatment for several 
years at least annually, and preferably 2 or 3 times during the early 
part of each dry season. 
Asclepiadaceae, or Milkweed, Family 
Asclepias curassavica L. (fig. 5) 
Kittie Mc-Wanie 
Description.—This perennial, sparsely branched weed is 2 to 4 
feet high. The stems are smooth and green when young and become 
gray with age. The thin leaves taper to points at both ends; they are 
up to 5 inches long and 1 to 2 inches wide near the middle. They 
are borne in pairs along the branches on short leaf stems. The small 
yellowish-orange, reddish, or bicolored flowers are held erect by short 
stems. Thespindle-shaped green fruits, 3 to 4 inches long, split length- 
wise when ripe and release numerous flat, brown seeds, each with a 
parachute of silky fibers that make them airborne. The plants are 
ordinarily reproduced by seeds; however, they may be increased by 
cuttings when used as ornamentals. Although the plants flower 
throughout the year in the more humid areas, they are most conspicu- 
ous during the wet season when they flower most profusely. 
DisrrizcTion aND Hapirar.—Kittie Mc-Wanie, a common weed on 
all the Virgin Islands, usually grows singly or in small patches. It is 
practically never found in forest or woodland but may grow almost 
anywhere else, especially in pastures in the higher rainfall areas, in 
both full sun and partial shade. The wide distribution of Kittie 
Mc-Wanie is partly attributable to its windborne seeds. 
Toxiciry anp Symproms.—All parts of Kittie Mc-Wanie contain 
the glucoside asclepiadin, of which large amounts cause death (45). 
The plant is not palatable to livestock and only under emergency 
conditions will animals eat it. Sheep are most often poisoned, but 
cattle and horses may also suffer poisoning if forced to consume the 
weed. One pound of the plant is sufficient to kill a sheep. Five to 
ten pounds may cause fatalities in cattle or horses (38). Poisoned 
animals become dull and stupid in a few hours. They lose muscular 
control, stagger, and finally fall to the ground. The pulse becomes 
rapid and weak, and breathing becomes labored. Death may be rapid 
when large amounts have been consumed. ; 
ManacGeMENT AND Controt.—Livestock should not be allowed access 
to areas where this species occurs. Although animals will not ordi- 
narily browse on the plants, they are a potential danger in areas 
609308 O—62——_2 
