STOCK-POISOXIXG PLANTS OF THE PvANGE 



29 



In past years the blue loco weed has been known mainly as a 

 horse-poisoning plant and has been responsible for heavy losses in 

 Arizona. However, it will affect also cattle and sheep, and recently 

 has caused much trouble with cattle. 



Wootox Loco Weed (Astragalus wootoni) 



Growing in western Texas, New Mexico, eastern Arizona, and 

 northern Mexico, Wooton loco weed resembles the true blue loco so 

 closely that frequently they are not distinguished from each other. 

 This loco weed, however, has larger inflated pods, and its leaflets are 

 somewhat narrower. It is considered especially poisonous to horses, 

 but it has been shown to affect cattle and sheep also. It is one of the 

 more poisonous locoes. 



Figure 16. — Blue loco weed growing in Arizona in April 



Half -moon loco weed, A. allochrous, shown in Plate 19, grows in 

 the same general localities, but on sandy soils. This is so much like 

 the Wooton loco weed that some botanists have not considered them 

 as separate species. 



Sheep Loco Weed (Astragalus nothoxys) 



Sheep loco (pi. 20), is a low, spreading plant which grows in con- 

 siderable abundance in southeastern Arizona and adjoining New 

 Mexico and Mexico. Single plants may be 2 feet in diameter. The 

 flowers are white-tipped or spotted with violet. The narrow pods 

 are about 1 inch in length. Experimental work with sheep and cattle 

 has shown that it is about as poisonous as the blue loco weed. Al- 

 though it is commonly known as the sheep loco weed, the main losses 

 have been of cattle. 



