406 CRAFTS 



placed a definite ceiling on production. It seemed for ages that the evolution 

 of pests was only one step behind the improvement of crops; and man's 

 destiny seemed to hang in the balance between them. The story of this 

 struggle, as exemplified by the activities of the U.S. Department of Agricul- 

 ture, has been aptly described by Quisenberry (1948). The story of the 

 strides recently made in insect and disease control I will leave for others to 

 tell. I would like to recall a few of the interesting episodes in the introduction 

 and spread of weeds and in the battle now being waged to bring them under 

 control. 



Some serious weeds. As examples of weeds that have seriously affected 

 American agriculture, I have selected Canada thistle (Cirsium arvense), 

 Russian thistle (Salsola kali var. tenuifolia), St. Johnswort (Hypericum 

 perforatum) , and Halogeton (Halogeton glomeratus). 



Canada thistle is a perennial weed prevalent throughout Central Europe, 

 including the British Isles. It was brought into the American colonies with 

 seeds and foodstuffs and was reported in Canada early in the seventeenth 

 century, and in New York by 1777 (Dewey, 1901). It spread rapidly during 

 the western migration and was found in California by 1879 (Robbins, 1940). 



A noxious weed that spreads both vegetatively and by seed, Canada thistle 

 early proved itself a serious menace to agriculture. It has been named as a 

 noxious weed in the seed laws of 37 states, and it is still spreading. Not only 

 has it invaded cultivated fields, but in the Northeast it is also penetrating 

 the more open areas in forest, park, and range lands where control is im- 

 possible. Its wind-borne seeds are carried into every possible site for germina- 

 tion; its dioecious habit is apparently no deterrent to its rapid spread; 

 its vigorous, competitive character enables it to dominate the flora in many 

 open areas that otherwise would produce good forage. The only factors 

 limiting its range seem to be climatic, and it apparently stays in the northern- 

 most tier of states. One hundred years of agronomic research have failed to 

 discover a practical method for eliminating Canada thistle; ten years after 

 the discovery of 2,4-D we are still seeking a satisfactory chemical method 

 for its control. 



Russian thistle is an annual of the tumbleweed habit; that is, at maturity 

 it breaks off at the ground line and is blown by winds so that its myriads of 

 seeds are effectively spread. It grows best under semi-arid conditions and 

 tolerates saline soils; it is a weed found in small grains, as well as on fallow 

 lands, abandoned fields, and nontilled areas. It makes its major growth during 

 summer and remains succulent well into autumn on most soils. 



Russian thistle was introduced into the United States from Russia around 

 1874 and was first reported from South Dakota (Robbins et al., 1952). By 

 1895 it had been reported in 16 states, including California. During World 

 War I many acres of marginal land were plowed and planted to wheat; after 

 the war these lands were abandoned and Russian thistle took over literally 



