150 



Hop-" Mould " and its Control. 



[May, 



HOP-" MOULD" AND ITS CONTROL, L 



E. S. Salmon, 



Mycologist to the Soutlt Eastern Agricultural College, 

 Wye, Kent. 



Introductory. — The disease known variously as " mould," 

 " red mould " or mildew is the cause in many seasons {e.g., in 

 1920) of serious financial loss to the hop-grower. The other 

 serious disease of the cultivated hop is the " fly " or hop- Aphis. 

 The modern hop-grower has fully acquainted himself with the 

 life-history of the Aphis and when it arrives he " washes " the 

 hop garden with such energy and technical skill that even the 

 most persistent attacks are kept under. 



The cause of hop-" mould " has only comparatively recently 

 been understood by the hop-grower. The farmer who still 

 believes that " mould " is due to certain atmospheric causes or 

 to the unhealthy condition of the sap of the hop-plant caused 

 by errors of cultivation or manuring is now rarely met. Most 

 farmers now not only recognise that " mould " is of fungous 

 origin, but know the main points in the life -history of the par- 

 ticular fungus concerned. Prof. J. Percival and Mr. A. Howard, 

 working at Wye College, largely helped in the spread of this 

 knowledge. The late Mr. W. H. Hammond, a hop-grower as 

 well as scientist, was the first to point out* that " red mould 

 and " mould " were two forms of the one disease. 



The fact that at the present day " mould " takes far too heavy 

 a toll of the crop in many quarters is due chiefly to the following 

 causes : — (1) Although the use of sulphur (an efficient remedy 

 against " mould ") is general, the farmer does not, as a rule, 

 use it early enough in the season. (2) The thorough control of 

 " mould " is dependent upon the taking of many indirect 

 measures, some of them cultural. (3) Too often the hop-grower 

 depends upon some utterly fallacious measure for controlling the 

 disease. 



It is the object of this article to treat the subject of ' ' mould ' ' 

 fully from these three standpoints. 



Life-history of the Hop-" mould " or Mildew. — A photo- 

 graph of a hop-leaf with several spots of " mould " is given in 

 Fig. 1. The general appearance, under a strong magnifying 

 glass or microscope, of a spot of hop-" mould " is shown in 

 Fig. 2. The " spawn " (mycelium) of the fungus (Sphcrrotheca 



* Journ. S.E. Agvic. Coll., IX, p. 19 (1900). 



