1922.] 



LDJE-SuLriirn as a Fungicide. 



997 



sprayed on to a *' powdery " patch of mildew, it will be found 

 that the fluid congregates in minute drops over the surface of 

 the patch, so that it becomes impossible to measure accurately 

 the fungicidal effect of the fluid, since parts of the fungus 

 remain unwetted. It is necessary, therefore, either to treat the 

 mildew with some substance such as a soft soap solution which 

 will cause it to be wetted all over by the lime -sulphur wash 

 applied subsequently, or to add some substance to the lime- 

 sulphur which will increase its wetting properties. Both these 

 lines of investigation were followed and gave remarkably 

 concordant results. 



In one set of experiments the patches of mildew were sprayed 

 first with a 1 per cent, solution of soft soap (which removed the 

 air entangled among the conidia and conidiophores , and wetted 

 all the parts), then with water to remove the soap solution, 

 and immediately afterwards with the lime-sulphur solution. 

 After the treatment with soap and then with water, it was found 

 that the mildew had not been appreciably affected, since by the 

 fourth day after spraying the mildew-patches were fully as 

 vigorous and as " powdery " as the unsprayed ones on the 

 " control " leaves, and also that the lime-sulphur solution when 

 applied to the "wet mildew-patch no longer collected on it in 

 drops, but ran through and wetted thoroughly each " powdery " 

 patch. 



Using this method, it was found that a commercial brand of 

 lime-sulphur, of 1.30 sp. gr., containing 16.57 per .cent, of poly- 

 sulphide sulphur, when diluted 1 part to 99 parts of water and 

 thus containing 0.16 per cent, of poly sulphide sulphur, was fun- 

 gicidal. By the fourth day after spraying all the mildew patches 

 on the spiked leaves (although still conspicuouslv white and 

 little altered to the naked eye) were quite dead, while the 

 " control '•' leaves (at the same " nodes ") which had been 

 "Sprayed only with the soap solution and then with water, bore 

 vigorous, densely powdery patches of mildew. 



Using the dilution of one part of the same concentrated lime- 

 sulphur to 199 parts of water, or 0.08 per cent, of poly sulphide 

 sulphur, it was found that while the majority of the patches of 

 mildew were killed, a few survived ; in other words, lime-sulphur 

 at this strength was apparently just beginning to break down as 

 an efficient fungicide. 



The preliminary treatment of the mildew with soap and then 

 with water, while useful for experimental purposes, cannot of 

 course claim to have any practical value. 



