350 



CONTROL OF WEEDS 



roots and underground stems are killed. Light and air are neces- 

 sary for the successful growth of any chlorophyll-bearing plants, 

 whether they are weeds or not. 



Smothering plants by means of tar paper, covers of manure, 

 straw or even with the growth of crops which over-shadow them 

 are methods resorted to in special cases. For example, such weeds 

 as persistent as Bermuda grass are sometimes killed by the growth 



Fig. 247. 



Fio. 248. 



Fig. 247. — Prickly Lettuce; 1, section of plant showing leaf arrangement; 2, top of plant; 



3, seedling; 5, seed natural size and enlarged. (Minnesota Station.) 

 Fig. 24S. — Crab Grass. 1, Entire plant; 2, enlarged flower spike; 3, seedling; 4, seedling 

 somewhat older. (Minnesota Station.) 



of a smothering crop such as alfalfa, millet or wheat. The smother 

 crop must be seeded densely to accomplish this end. 



Seed Laboratories to Control Weeds. — Seed laboratories have 

 been established in nearly all the states for the control of the weed 

 nuisance. Regulations and laws are published which fix the stand- 

 ard for purity of seeds sold in the state, as well as standard for 

 germination. Samples are examined in the laboratories and bad 

 lots of seed are condemned. 



Farmers and gardeners are able to choose seeds which have 

 been tested for both purity and germination. Too often the sower 



