60 FARM FRIENDS AND FARM FOES 



season, it is likely to be less dangerous than if it lives 

 two or more seasons. Like other plants, weeds are com- 

 monly grouped as annuals, living but one year, biennials, 

 living two years, and perennials, living many years. The 

 phrase winter annuals is given to those plants that start 

 their growth in autumn and finish their development the 

 following spring or summer. 



The remedial measures to be taken against weeds depend 

 largely upon the term of life. The annuals live from year 

 to year by means of their seeds. Consequently the preven- 

 tion of seeding by tillage or other means and the destruction 

 of the seed are the most important general measures. It 

 has lately been found that some annuals like the mustards 

 may safely be killed in grain fields by spraying with a weak 

 solution of iron sulphate. The biennials reproduce also 

 by seeds, and are to be treated much as the annuals. The 

 perennials commonly reproduce both by seeds and by root- 

 stocks or other vegetative growths, so that their destruction 

 is generally more difficult than in the case of the annuals 

 and biennials. 



The methods that may be employed for the destruction 

 of the roots or rootstocks of perennial weeds have been 

 well summarized by L. H. Dewey in these words : 



(1 ) They may be dug up and removed, a remedy that can 

 be practically applied only in small areas. 



(2) They may be killed by applying chemicals either to 

 the freshly cut root or at the base of the main stem. Salt, 

 strong brine, coal oil, crude sulphuric acid, and carbolic 

 acid have been successfully used for this purpose. A few 

 drops of carbolic acid applied at the base of the main stem 

 with an ordinary machine-oil can is the best method that 

 has been yet devised for killing weeds with chemicals (ex- 

 cept spraying with sulphate of iron). 



