58 WEEDS OF FARM LAND 



may be broadcasted or scattered by machine early in the 

 morning while the leaves are still wet with dew. 



All cereal crops, and also the leguminous crops sown 

 among them, will resist dusting or spraying with iron sulphate. 

 The leguminous plants owe their immunity, in this case, to 

 the fact that they are to a great extent protected by the larger 

 growing weeds and the cereals, so that comparatively little of 

 the spray reaches their leaves. Serradella, however, growing by 

 itself, will not stand spraying with any dilution of iron sulphate 

 or at any stage of growth, so that it has proved impossible to 

 use this means of eradicating wild radish among this crop. 

 Nearly all unprotected broad-leaved crops growing alone suffer 

 badly, and beans, vetches, yellow and white lupins, roots and 

 potatoes are much injured by the iron sulphate, though peas 

 and blue lupins are rather less sensitive. 



The iron spray is more effective than the copper salt in 

 dealing with poppies and corn buttercups, a I 5 per cent, solu- 

 tion reducing the weeds drastically. For the buttercup the 

 spray is best applied at the beginning of February, and a 1 5 

 per cent, solution may be used as this is known to do no 

 permanent harm to the cereal crops. 



Sulphuric Acid. This is the most corrosive agent that is 

 used in the eradication of weeds. It attacks metals violently, 

 including copper ; therefore it is necessary to use special spray- 

 ing machines and to wash them out thoroughly immediately 

 after use to prevent them from being eaten away. Italian ex- 

 periments indicate that if spraying is done at the right time the 

 production of the cereal crop is not affected. For wheat it 

 should be used during February and early March, when the 

 plants have five or six leaves, at the rate of about 90 to ico 

 gallons per acre of an 8 or 10 per cent, solution made up with 

 water. This method has been used in France, in Lot-e-Garonne, 

 for destroying wild radish. 1 Sulphuric acid does not act as a 

 universal weed destroyer, as all the weed grasses, including 

 wild oat (Avena fatud], resist its action because their habit 

 resembles that of the cereals. Medicks (Medicago spp.) and 

 members of the lily family (as wild onion) also escape. The 

 acid is deadly to most annual and biennial weeds, such as 

 poppy, charlock, corn buttercup, cornflower, wild carrot, wild 

 radish, vetches and vetchlings, and it clears badly infested 



1 Rabatd, E. (1911), "Destruction des Ravenelles par 1'acide sulfurique," 

 Jour, d 1 Agriculture pratique, No. 13, pp. 407-409. 



