CEREAL PESTS WEEDS 461 



This thistle is very difficult to eradicate. First, no 

 plants should be allowed to mature seeds. The scythe or 

 mower may have to be used to cut out large patches in the 

 grain field. Afterward, deep plowing, bringing roots to 

 the surface to be exposed to winter freezing, and constant 

 cutting back of the tops will greatly weaken the growth. 

 A 3-years rotation of barley clover corn, following this 

 preparatory treatment, will so nearly complete the eradi- 

 cation that a renewal of the growth can be prevented by 

 careful watching. The thistle rust (Puccinia suaveolens) 

 sometimes kills the plants to the ground, but rarely or 

 never kills all the plants in a patch. 



505. Bindweed or perennial morning glory (Conwl- 

 mdus spp.). This weed, including three species and one 

 variety, occurs almost throughout the United States. 

 Although widespread in Canada, and troublesome in 

 restricted localities, it is said to be not yet a very common 

 weed in that country. It is found most often on deep 

 bottom lands and on rich prairie soils. It is therefore 

 worst on the most valuable land. 



East of the meridian of 100 the native hedge bind- 

 weed (Convolvulus sepium, Linn.) is the most common 

 species (Fig. 145). West of that line the field bindweed 

 (C. arvensis, Linn.) is probably the most common. A 

 trailing form (C. repens, Linn.) with downy leaves has 

 become a serious weed in wheat in central western Kansas. 

 The fourth species of importance as a weed (C. califor- 

 nicus) is found in California. 



The hedge bindweed has a long twining stem ; leaves triangular, 

 arrow-shaped, with basal lobes pointing outward; flowers funnel- 

 form, resembling those of the cultivated morning glory, but always 

 white or rose colored ; base of the flower inclosed in bracts f inch 

 long. The field bindweed is either trailing or twining ; leaves ovate, 



