142 



Dry Spraying of Charlock. 



[May, 



(3) The Garforth experiment of 1920 shows that when the 

 sulphate of copper is finely ground, an application of 20 lb. to 

 the acre is sufficient to destroy the Charlock plants, provided 

 seed has not set. In the majority of reports of experiments on 

 Charlock spraying, emphasis is laid on the necessity of spraying 

 the plants when in the third or fourth leaf, but, from our experi- 

 ence, we are inclined to think that the best results are likely 

 to be obtained if the spraying is carried out just as the plants 

 are bursting into flower. The flower-heads are very. easily killed, 

 and the leaf surface exposed to the action of the spray is at this 

 time greater* than in the case of younger plants. The effective- 

 ness of the spray is thus increased, and the plants are less likely 

 to recover. 



(4) There appear to be a number of Dry Spray machines 

 on the market. We have not tested any of these person- 

 ally, but some of them should be easily adaptable to the 

 spraying of Charlock. Two of those which have been brought 

 to our notice are said to distribute quantities as small as or 

 smaller than 20 lb. to the acre, and this being the case, the 

 necessity of adding any diluent to the sulphate of copper, as 

 was done in the Knapsack machine, would no longer arise. 



(5) A comparison of the relative cost of Wet and Dry Spraying 

 shows that, in this respect also, the latter process compares very 

 favourably with the former. In wet spraying, the formula 

 recommended by recent trials is 16 to 20 lb. of copper sulphate 

 in 40 gall, of water, this making a solution sufficient to spray 

 an acre. In dry spraying, we have suggested 20 lb. of copper 

 sulphate to the acre; in this case, however, there will be a 

 slight additional charge for grinding the material, but this is 

 not likely to exceed 5s. a cwt. On the other hand, the labour 

 entailed and the time expended in the newer process is very 

 considerably less than that required in the older. 



We consider, therefore, that provided an efficient machine is 

 nsed for the purpose, the destruction of the Charlock pest by 

 dry spraying should recommend itself to many farmers, and in 

 particular to those who live in the more waterless districts of 

 the country, where the older method has always been so heavily 

 handicapped. 



We wish to express our thanks to Mr. H. Beachell and Mr. 

 Wilson for their kind co-operation in carrying out the trials on 

 their farms, and also to Mr. J. Manby, of the University of 

 Leeds, for the photographs. 



