Common St.Johnswort is a very aggressive, moderately poisonous 

 range weed pest introduced from Europe first reported in New 

 England about 1800, and growing on the Pacific coast since 1900. 

 It does not seem to be regarded as a very serious weed pest through- 

 out the Middle West and East, but is firmly established and spread- 

 ing in the Pacific Coast States, especially in northern California. 

 It occurs less extensively in Montana, Idaho, and Utah, although, at 

 present, also increasing its range in these States. The common name 

 St.Johnswort has come from the Old World, where according to 

 legend it bloomed on June 24, St. John the Baptist's Day. 1 This 

 species is commonly known in California and Oregon as Klamath 

 weed, as the original infestation came from the Klamath River 

 country near the Oregon line. 



This species usually establishes itself on eroded pastures and aban- 

 doned or poorly cultivated fields, although it also becomes abundant 

 on adjoining deep and fertile soils. It prefers full sunshine on well- 

 drained slopes and never grows satisfactorily in shaded areas, or 

 where the soil remains moist. This plant flourishes at low eleva- 

 tions and probably does not occur above the ponderosa-pine belt in 

 any of the western States. Since this weed usually grows in pas- 

 tures and fields, its associates include such grasses as annual fescues, 

 wild oats, and broines as well as perennials like needlegrass and 

 bluegrass. However, once well established it forms dense patches or 

 even extensive fields, and dominates the soil to the exclusion of 

 practically all other herbaceous vegetation. The mature plants are 

 woody and, as a rule, unpalatable ; the young spring shoots, however, 

 furnish fair forage for goats, and are sometimes grazed lightly by 

 sheep and cattle. The weed is heavily grazed only where animals 

 are forced to consume it and, under such starvation conditions, sick- 

 ness and losses are most likely to ensue. 



Common St.Johnswort has long been recognized as a poisonous 

 plant, although it is toxic only to white or unpigmented animals. 

 This curious situation is probably due to some fluorescent substance 

 in the plant which exerts harmful effects when absorbed by white- 

 skinned animals that are subsequently exposed to full light. 2 Ap- 

 parently all parts of the plant are toxic; well-bred and young ani- 

 mals react most readily to the poison. Marsh and Clawson's 3 

 feeding experiments show that cattle are more susceptible than 

 sheep. Briefly, these investigators ascertained that the consumption 

 of green foliage equivalent to 4 percent of the animal's weight 

 poisoned sheep, but as little as 1 percent was toxic to cattle, with 5 

 percent probably fatal. Sensitiveness varies with individual ani- 

 mals, as some are not poisoned by repeated dosages, yet others sicken 

 in a few hours and continue to show symptoms even a month after 

 the feeding of this weed is discontinued. The first symptoms are 

 increased pulse, temperature, respiration, and general uneasiness, 

 probably caused by intense skin irritation. Later, blisters and a 



1 Bailey, W. W. ST.JOHNSWORT. Amer. Bot. 15 (3): 68-70. 1909. 



2 Rogers, T. B. ON THE ACTION OF ST.JOHN'S WORT AS A SENSITIZING AGENT FOE NON- 

 PIGMBNTED SKIN. Amer. Vet. Rev. 46 : 145-162, illus. 1914. 



3 Marsh, C. D., and Clawson. A. B. TOXIC EFFECT OF ST.JOHNSWORT (HYPERICDM J>ER- 

 FORATUM) ON CATTLE AND SHEEP. U. S. Dept. Agr. Tech. Bull. 202, 24 pp., illus. 1930. 



