PREVENTION AND ERADICATION OF WEEDS 57 



ened by the addition of a soluble manure, which acts as a 

 stimulant and enables the crop to get ahead of the weeds before 

 any that may survive have time to recover. Corn butter- 

 cup (Ranunculus arvensis), if very strong, is only burnt and 

 not destroyed by a fairly strong solution of copper sulphate, 

 4| per cent In one experiment 1 the amount of chemical 

 was more than doubled, to 9-9 per cent, and 22 Ib. of 

 sodium nitrate was added to the 10 gallons of water. About 

 35 to 40 per cent, of the weeds were killed or injured, and before 

 the rest could make much growth the wheat had benefited so 

 much by the nitrate that it pulled right ahead of the weeds. 

 Such strong applications of copper sulphate, however, need 

 very careful handling, and are not to be advised under ordinary 

 circumstances. 



Iron Sulphate. In most cases this can be. used as a sub- 

 stitute for copper sulphate, and very often the iron compound 

 is the more effective of the two, provided that suitable strengths 

 are employed, as stronger concentrations of the iron salt 

 are necessary. It has been largely used abroad to eradicate 

 charlock, and experiments have also been carried out in this 

 country. Quite good results have been obtained with 40 

 gallons of 7 per cent, solution per acre, particularly on oat 

 crops. It was found that copper sulphate caused the young 

 oats to flag more than the iron sulphate, but, on the contrary, 

 young barley received more initial check from the latter spray. 

 Hiltner 2 used a far more concentrated solution in larger 

 quantities, applying 53 gallons per acre of a 22 per cent, 

 solution to infested oats. Excellent results were obtained, 

 and the yield of oats from a plot treated thus was six times 

 that from an untreated plot. Care was taken that the plants 

 were completely dry before the spraying was done, and the 

 drastic effects on the charlock were visible within two days. 

 The German Agricultural Society 3 recommend the addition 

 of 5' per cent, of molasses to cause the solution to adhere to 

 the weeds more firmly. Iron sulphate may also be applied 

 dry as a fine powder, 4 at the rate of 3 to 4 cwt per acre. It 



1 Martin, J. B. (1916), C.R. de V Academic d? Agriculture de France, II, pp. 

 420-424. 



2 Hiltner (1911), Praktische Blatter fur Pflanzenbau^und Pflanzenschutz, 

 Jan., Feb., Summ. in Jour. Bd. Agric., XVIII, pp. 41-42. 



3 Mitt, der deut. Landw. Gesell. (1911), Flugblatt, No. n, Summ. in Jour. 

 Bd. Agric., XVIII, p. 244. 



4 Bull. Soc. Nat. d" 1 Agric. (1909), No. 5, Summ. in Jour. Bd. Agric., XVI, 

 p. 761. 



