B. P. I.— 340. 



RESULTS OF LOCO-WEED INVESTIGATIONS 

 IN THE FIELD." 



By C. Dwight Marsh, Expert, Poisonous-Plant Investigations. 



FIELD WORK. 



The word " loco," from the Spanish, meaning crazy,, has been ap- 

 plied for a great many years to a disease of stock and sheep in the 

 semiarid region of the West. There has been a general belief among 

 stockmen that the disease is caused by certain weeds known as loco 

 weeds. The name loco weed has been applied to a large number of 

 plants, but two are considered especially obnoxious — Aragallus 

 larnberti and Astragalus mollissimus. 



More or less desultory investigations by scientific men have been 

 made on this subject, the general result of which has been to imply 

 that the disease was produced by some other cause than the loco 

 plants. The later investigations have made it seem quite probable 

 that the cause of the disease must be sought in some other direction. 

 The investigations here recorded were undertaken to clear up first of 

 all the doubt concerning the source of trouble. 



The first essential point was to demonstrate whether the loco weeds 

 did or did not cause the disease. The work of the first season, the 

 summer of 1905, accomplished this demonstration in a very satisfac- 

 tory way. It was clearly proved that Aragallus larnberti would 



a For many years stockmen of the plains east of the Rocky Mountains have 

 reported great losses due to a somewhat undefined cause known as " loco." It 

 has been estimated that the losses from this source in Colorado alone have 

 reached the sum of a million dollars per annum. A thorough investigation of 

 the loco problem by the Bureau of Plant Industry, both in its field and labora- 

 tory aspects, was undertaken by the office of Poisonous-Plant Investigations, 

 under the direction of Dr. Rodney H. True, Physiologist in Charge, the field 

 work being in the hands of Dr. C. Dwight Marsh, Expert, and the laboratory 

 work in those of Dr. Albert C. Crawford, Pharmacologist. 



The importance of the results obtained, together with the fact that the publi- 

 cation of the rather extensive evidence accumulated is likely to be somewhat 

 delayed, has made it seem desirable to present at once a brief summary of the 

 results obtained— B. T. Galloway, Chief of Bureau. 



121— in 37 



