156 



Hop-" Mould " and its Control. 



[May, 



the air over several alleys — to take the machine down every 

 second or third alley through the garden in the first operation, 

 and then on subsequent occasions to go down the alleys 

 previously missed. The sulphur will always readily adhere to 

 any spots of " mould," but if a slight dew is present, it will stick 

 better to the hop-leaf; absence of wind at the time of the opera- 

 tion is highly desirable, and such a condition is most frequently 

 obtained in the early hours of the morning. 



The purest " flowers of sulphur " should be used in all 

 the operations, and such adulterated forms as " green 

 sulphur," " black sulphur," " sulphur vivum " should be 

 strenuously avoided.* Kecent evidence gives ground for 

 believing that sulphur does not act in a gaseous form, and that 

 direct contact of the mildew with a particle of the sulphur is 

 necessary for its destruction. Contrary to general belief, the 

 heat of direct sunlight is not required in order to make sulphur 

 efficacious in killing " mould." The writer has observed 

 repeatedly in experiments that when a particle of sulphur 

 adheres to the mildew, a slow shrivelling up of the fungus takes 

 place, even when it is kept continuously in the shade (Fig. 9). 

 In order to get the best results in sulphuring against " mould," 

 the observance of two points is essential: (1) the " flowers 

 of sulphur " must be of a brand guaranteed to be pure sublimed 

 sulphur and free from admixtures, and (2) it must be in a 

 condition of very fine, dry, dust-like particles free from lumps 

 or " caked " masses. If the sulphur has become " caked " it 

 must be passed through as fine a sieve as possible. The finer 

 the particles the greater will be the number of points of con- 

 tact, and a quicker and more thorough destruction of the 

 mildew will be the result. 



There seems little doubt that in wet weather " mould " is 

 not kept under satisfactorily by " flowers of sulphur," probably 

 because of the removal of the latter by the rain. Some growers 

 use in dull or wet weather a solution of " liver of sulphur " 

 (poly sulphides of potassium or sodium). The strength usually 

 advocated is from 1 to 2 lb. of " liver of sulphur " to 100 gal. 

 of water or of " hop-wash." Experiments have shown t that a 

 " liver of sulphur " solution of this strength does not kill hop- 

 " mould," even when used with 10 lb. of soft soap to the 100 gal. 

 of water, and that from 3 to 4 lb. of " liver of sulphur " is 



* A sample of a much-advertised brand of "green sulphur" contained only 

 25 per cent, of sulphur, while the other constituents (including sulphate of lime 

 (gypsum) 40 per cent.) were of no known fungicidal value. 

 ' f ./. V. Eyre and E. S. Salmon, in Jourv. Agric. Science, VII, 473 (1916). 



