WHORLED MILKWEED 
The Worst Stock-Poisoning Plant 
in Colorado 
By W. Li. MAY, Assistant Botanist 
The investigative work on the whorled milkweed in Colo- 
rado, carried on during the past two summers, has demonstrated 
that this plant is the most dangerous poisonous plant in the 
State, both because of its toxic properties and because of its ex- 
treme resistance to eradication measures. The importance of 
the problem justifies continued effort and expense on a larger 
scale than has so far been employed. The problem is not yet 
solved, but enough has been done to justify placing before the 
stockmen and farmers of the State the results of the work so far 
done. 
LOSSES CAUSED BY WHORLED MILKWEED IN COLORADO 
It has Tong been known to medical science that the various 
species of Asclepias possess toxic and medicinal properties, and 
the members of the genus have long been viewed with suspicion 
as being poisonous, but it is only recently that particular atten 
tion has been directed to the species under discussion as being 
a very dangerous stock-poisoning plant. At the present time it 
is definitely established that Asclepias qalioides has been responsi- 
ble for very hea^^^ annual losses of sheep, cattle, and horses 
in Western and Southwestern Colorado, and it is suspected that 
the plant has been the cause of some unexplained losses in Huerf- 
ano and Las Animas Counties and in the irrigated sections along 
the Arkansas River from Canon City to the state line. 
The earliest case on record at this station of the heavy loss 
probably due to ‘‘whorled’^ or ‘‘bedstraw milkweed”’ is that of the 
loss of 85 head of lambs by Mr. W. E. Ryman, a sheepman near 
Colona, Colorado, in 1909. These lambs were poisoned in an 
orchard containing much of the milkweed and Mr. Sam Phillips, 
a neighbor of Mr. Ryman, reported to the writer in 1918 that the 
state veterinarian at that time suspected the milkweed as being 
responsible. 
