24. 



of half a century. No matter how much cultivation you give 

 the soil a new crop of weeds will appear. 



Sweet Clover. This biennial weed is common in many parts of 

 the state. It produces a tap root which is not difficult to exter- 

 minate by cultivation. As in the preceding case the seeds retain 

 their vitality a long time. 



Greater Ragweed or Kinghxad. This weed is a troublesome 

 pest in many Iowa fields along fences and railroads. The plants 

 are easily destroyed in fields by cultivation. The seed probably 

 retains its vitality for some time. Iron sulphate, 100 pounds 

 to a barrel of water will destroy it. Plant clean seed. 



Nimble Will or Drop-Seed Grass. This station has received 

 many letters complaining about this weed. The character of the 

 "roots" is so different from that of the roots of quack grass and 

 the other perennial weeds that we have mentioned before that it 

 is not difficult to exterminate. The roots of this weed and the 

 allied species are more or less clustered. In an experiment con- 

 ducted to exterminate this weed we found that by giving a 

 shallow plowing of four or five inches and harrowing to expose 

 the roots to the sun, they were killed, no growth making its ap- 

 pearance during the rest of the season. Of course this is not 

 effective during rainy weather. 



Cocklebur. The cocklebur is a serious menace to cultivated 

 crops in many parts of the state, more especially in southern 

 Iowa. The best method of combating the cocklebur is the rota- 

 tion of crops and clean culture. When a field is in corn, the 

 field should be thoroughly cultivated and none of the plants al- 

 lowed to mature seed. If they cannot be caught by the cultiva- 

 tor, it may pay to kill the remaining plants with a hoe, or to pull 

 them by hand. The corn should be followed with winter rye and 

 then oats, using the oats as a nurse crop for clover and timothy. 

 Leave the field in meadow for at least two years and then if pos- 

 sible turn it into pasture. This certainly eradicated the cockle- 

 bur, ragweed and many other annual weeds. 



Summer Fallow. Undoubtedly this is a splendid method for 

 the eradication of weeds. I am not using the term, however, as 

 it is ordinarily used. To plow and then leave fallow for the 

 summer, but constant cultivation and harrowing must be resorted 

 to in order to remove the weed. The field must be kept free from 

 weeds during the summer and fall. 



The Use of Chemicals. In recent years many experiments have 

 been made with various chemicals to destroy weeds. Among 

 them iron sulphate, sodium arsenite, corrosive sublimate, copper 

 sulphate and common salt. 



Some of these substances like sodium arsenite and corrosive 



