WEEDS AND THEIR CONTROL 217 



Among the influences by which man aids weed distribu- 

 tion are (1) importing weedy foodstuffs including hay, 

 (2) sowing impure seed, (3) neglecting road allowances 

 and railway rights-of-way and freight yards, (4) using 

 weed-infested, undeeayed farm yard manure, (5) cus- 

 tom threshing, and (6) by tillage machinery in moving 

 from dirty roads or fields to clean fields. 



Fig. 77. — Tumbling Mustard Piling Up Against a Fence. 

 The Russian Thistle, another weed of tumbling habit is a serious 

 menace to farmers in South Western Manitoba, South Western Saskat- 

 chewan and Southern Alberta. 



The chief natural agencies resulting in the distribu- 

 tion of weeds are the wind, water, animals and birds. 

 The wind scatters (a) fluffy or hairy seeds such as 

 Dandelion, Canada thistle and Sow thistle, (b) winged 

 seeds such as Dock and Parsnip, (c) seeds having ex- 

 tended edges such as Penny Cress, (d) plants that roll 

 like Russian thistle and Tumbling mustard, (e) sticky 

 seeds like Plantain adhering to weeds that blow, and 

 (f) weed seeds in drifting soils. Irrigation water, 

 flood streams, and rapid "run off" water also distribute 



