PREVENTION AND ERADICATION OK WEEDS 59 



fields of these pests very effectively. 1 For oats it is advisable 

 to use about 60 to 70 gallons of the 10 per cent, solution per 

 acre, and rather less for barley. 2 



Arsenite of Soda. The very poisonous nature of this 

 substance has prevented it from coming into general use for 

 spraying purposes, and as it also has certain effects upon the 

 soil it needs handling with much judgment. It is widely used 

 in rubber plantations in Hawaii and among sugar canes in 

 Australia, and in the latter case it is claimed that its use has 

 reduced the cost of weed destruction by 25 per cent. 3 Arsenite 

 of soda, like most caustic sprays, cannot be used on the broad- 

 leaved crops without injuring them. In one attempt to rid 

 alfalfa of dodder by this means the alfalfa was killed as well 

 as the dodder. Besides this, there is danger of poisoning stock 

 if a fodder or hay plant is sprayed with too much of it. The 

 spray considerably alters the mechanical condition of the soil, 

 acting as a deflocculating agent It is strongly fixed by the 

 soil and is not washed out even by very heavy rains, and con- 

 sequently it is liable to remain for an indefinite time in the top 

 few inches. 4 For this reason it is unwise to use the sodium 

 arsenite spray too freely, as it may accumulate in the surface 

 soil in sufficient quantity to act as a poison to any crop that is 

 planted. With due care, however, and with particular crops, 

 there is no doubt that this spray is decidedly efficacious. 



Various Sprays. In view of the difficulty in obtaining 

 some of the more usual chemical sprays, such as copper and iron 

 sulphate, various experiments have been made with other 

 promising substances. At Rothamsted charlock plants in 

 various stages of growth were sprayed with 3 per cent, solutions 

 of nickel sulphate and copper sulphate to contrast the effect of 

 the two. With young plants the nickel spray was much slower 

 in taking effect than the copper spray, but at the end of six 

 days all the plants were dead and made no recovery. With 

 6 per cent, solution the action was rather more rapid. Later 

 on some very large plants just coming into flower were sprayed 

 in a similar way, but although a few days afterwards the 



1 Morettini, A. (1915), Le Stazioni sperimentali agrarie italiane, XLVIII, 

 pp. 693-716. 



a Jaguenaud, G. (1912), " Sur la destruction des mauvaises herbes dans les 

 Ce're'ales par 1'acide sulfurque," Le Progres Agricolc e Viticole, 29, pp. 332-334. 



s " Weed-killing by Machinery " (1916), Queensland Agric. jfovr., V, Part 2, 

 p. 61. 



* McGeorge, W. T. (1915), Hawaii Agric. Expt. Station, Honolulu, Presf 

 Bull., No. 50. 



