56 WEEDS OF FARM LAND 



Copper Sulphate. This is probably the most familiar of 

 all weed sprays, and has been experimented with for years. 

 It is most generally associated with the destruction of char- 

 lock (Brassica sinapis], but its use has been extended to other 

 weeds. The rough crinkled leaf of charlock makes it a most 

 favourable subject for eradication by spraying, and, given 

 suitable weather, the treatment rarely fails to make a consider- 

 able reduction. It is usually best to spray when the weeds 

 are small, with three or four well-developed leaves, but under 

 favourable conditions success will often attend much later 

 spraying. On a farm in Gedling, Notts, a few years ago 

 charlock was successfully sprayed when in full flower, but this 

 practice is not one to be recommended. On the same farm 

 it was noticed that while most of the charlock succumbed a 

 number of plants remained uninjured : closer investigation 

 showed that the latter were a different species, Brassica cam- 

 pestris, which has smooth, rather waxy leaves, off which the 

 spray rolled without exercising its corrosive action. Various 

 experiments indicate that the best strength to use is 4 or 5 

 per cent. (4 or 5 Ib. copper sulphate in 10 gallons of water), 

 applied at the rate of about 40 gallons per acre. In some 

 cases a 3 per cent, solution is effective, but only under specially 

 favourable conditions. 1 



A 5 per cent, solution of copper sulphate at the rate of 

 50 gallons per acre is useful for eradicating spurry and does 

 its work thoroughly, but a weaker strength, 3 per cent, is only 

 partially effective and allows about half the weed crop to form 

 and ripen its seeds. 2 3 In the latter case the spurry is injured 

 and checked at first, as the shoots shrivel and become brown 

 at the tips, but later on many plants recover considerably. 

 This recovery is prevented by the use of the 5 per cent, solu- 

 tion. Poppies are sensitive to this spray, and even a 2 per 

 cent, solution does them harm. It has been suggested that 

 two applications of a 3 per cent, solution, with an interval of a 

 few days, might prove quite effective in eradicating them. 4 



In some cases the action of the corrosive spray is strength- 



J " Charlock Destruction" (1909), Bull. I, Agric. Dept., Univ. Coll., N. 

 Wales, Bangor. 



2 "Spraying of Charlock and Spurry" (1908), Bull. II, Agric. Dept., 

 Univ. Coll., N. Wales, Bangor. 



3 " Destruction of Spurry in Corn" (1906), Bull. IX, Agric. Dept., Univ. 

 Coll., N. Wales, Bangor. 



4 "A Common Weed The Poppy" (1909), Jour. Bd. Agric. XVI, pp. 

 26-31. 



