WEEDS AND THEIR CONTROL 233 



one should endeavor to prevent the appearance of any- 

 young thistles above ground. This requires frequent 

 thorough cultivation, but, given favorable weather, will 

 result in the gradual death of the creeping root stocks 

 by starvation, because they cannot be nourished if green 

 leaves are prevented from forming. A "green" fallow 

 may be advisable occasionally throughout the fallow year 

 for controlling wild oats but a "black" fallow is essential 

 for the control of perennial weeds. If a field is infested 

 with wild oats and perennial sow thistle the fallow should 

 be planned to kill the most prevalent weed since the two 

 cannot be satisfactorily eradicated the same year. 



182. Poisonous or Otherwise Injurious Weeds. — Poison- 

 ous weeds are seldom found growing on cultivated fields. 

 They are usually found in native pastures or low uncul- 

 tivated areas where tillage is never given. The most 

 commonly found poisonous plants are Water Hemlock, 

 Dwarf Larkspur, Tall Mountain Larkspur, Purple 

 Larkspur, Small Larkspur, Woolly Loco Weed, White 

 Loco Weed, Poison Ivy, Lupines, Death Coma, Night 

 Shade, Corn Cockle and Cow Cockle. The Crocus or 

 Prairie Anemone is not poisonous but sometimes results 

 in the death of sheep by the formation in the stomach of 

 balls of the hairs that grow so profusely on the stems. 

 Spear grass is sometimes injurious to sheep for a time 

 when the "spears" are being shed, and to other animals 

 when fed in hay, by the spears penetrating the flesh. 



