WEEDS OF ARABLE LAND 61 



strongly, and destroys immense numbers of seedlings. 

 Sometimes also the seeds of Charlock may be en- 

 couraged to germinate in a mild autumn, when the 

 young plants are destroyed by the first sharp frost. 

 An important plan, which should be more often 

 practised, is to use a trough on the harvester or 

 binder when cereal crops are cut, in order to catch 

 the Charlock and other seeds which are shed, and 

 prevent them from reaching the ground (see p. 30). 



The third method, spraying, is of great importance, 

 and may be carried out when the cereal crop and 

 the Charlock are both young. The narrow, smooth, 

 erect leaves of the cereal do not retain much of the 

 solution used, and consequently escape any permanent 

 injury, while the somewhat broad, rough, horizontal 

 leaves of Charlock catch and retain the solution, and 

 are thus permanently damaged. In May and June, 

 when the Charlock plants are in the " rough leaf," and 

 not over 3 inches high, and while the cereal is still 

 comparatively short, the whole may be sprayed with a 

 2, 3, or 4 per cent solution of copper sulphate (8, 12, or 

 1 6 Ib. in 40 gallons of water), applying 40 gallons per 

 acre by means of a machine which generates a fine 

 spray under air pressure. Soft water should be used 

 when possible, the copper sulphate should be of 98 per 

 cent purity, and wooden buckets or tubs should be 

 employed for mixing. 



Sulphate of iron at the rate of 40 gallons per acre of 

 a 15 per cent solution (60 Ib. in 40 gallons of water) 

 may be employed in place of copper sulphate. 



Such spraying, if well done, results in a large pro- 

 portion of the young Charlock then growing being 

 killed (see also p. 45). The seeds of Charlock 

 contain a considerable amount of oil, and it is stated 

 by Percival that they are sold by many farmers to oil- 



