X. THE EFFECT OF DOUBLE SPRAYING 



In a few cases the crops were sprayed twice on the same 

 day, a plan that was found to answer well, and it appeared that 

 double application is an advantage even if the solutions used be 

 somewhat weaker. 



When inspecting the experiments it was noticed at many 

 of the centres that a second batch of plants had grown since 

 the spray had been applied. If a second application had been 

 used after an interval of about ten days this second crop also 

 would have been destroyed. 



On account, however, of the great demand for trials with 

 the sprayer, we did not succeed in returning a second time to 

 any of the centres to put this plan to the test. 



XL THEORY OF THE ACTION OF THE 

 SPRAY ON CHARLOCK 



Nothing certain is known with regard to the specific 

 action of solutions of Sulphate of Iron and Sulphate of Cop- 

 per on charlock plants. The point requires careful considera- 

 tion, and is at present being investigated by Mr. Ingle, 

 agricultural chemist to this department. 



It cannot be due to the roughness of the charlock leaves 

 retaining the spray, for there are many other plants which 

 retain the spray equally well and yet escape injury. In all 

 probability the result is due to the fact that cruciferous plants 

 contain certain substances peculiar to their order — substances 

 which may react chemically with iron or copper salts. 



In summing up the experience gained in spraying 144 

 acres of charlock and runch infested grain crops in Yorkshire, 

 we may conclude : 



1. That the operation is only completely successful when 



the plants are taken in the youngest stage. 



2. That a bright, dry and calm day is a necessary factor 



to success. 



3. That in the case of Sulphate of Iron at least a 10 per 



cent solution is required, and this should be applied 

 at the rate of not less than 40 gallons per acre. 

 Even a 15 per cent solution of Sulphate of Iron 

 may be necessary if the plants have got beyond the 

 first rough leaf stage. 



4. Such solutions will not injure either corn or young 



seeds. 



