CHAPTER THIRTY-FIVE 



WEEDS AND THEIR CONTROL 



The term " weed " is commonly applied to any undesirable 

 plant, and to any plant growing out of place. Rye may become 

 a weed in wheat fields. Red clover is very desirable in a field on 

 the farm, but it becomes a weed when it springs up in a lawn. 

 The most pernicious weeds, like the dandelion, cockle bur, 

 Canada thistle, poison ivy, bindweed, plantain, and sand bur, 

 are not desirable plants anywhere. 



Weeds decrease the yield of crop plants, reduce the value of 

 grain and seed crops, interfere with the growth and use of forage 

 crops, and greatly increase the cost of agricultural production. 

 Many weeds are conspicuous and unsightly on farms and lawns 

 and thus depreciate the value of land. Some weeds are harmful 

 or poisonous to stock, and others impart unpleasant tastes to 

 farm and dairy products. Weeds may also harbor injurious 

 insects and the bacteria and fungi that produce disease. One 

 of the commonest sources of hay fever and asthma is the wind- 

 borne pollen of ragweed, horseweed, and other weeds. 



High reproductive capacity. Weeds are plants in which re- 

 production has reached the highest degree of efficiency. The 

 sequoia may stand for the culmination of vegetative efficiency, 

 the dandelion for efficiency in reproduction and dispersal. The 

 dandelion produces good seed without pollination ; if the stem 

 is cut, the plant develops numerous new sprouts ; if the root is 

 cut into small pieces, each piece may sprout from either end or 

 from both ends at the same time. The dandelion can thrive in 

 a swamp, and it can withstand the droughts of a sand plain. 

 The sequoia still occupies the comparatively small area to which 

 it was restricted during the glacial-period. The dandelion has 

 in recent times spread to all parts of the world, and it occurs in 

 most habitats, from the seashore to the alpine summits of moun- 

 tains. 



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