ON FORMS OF THE HOP {HUMULUS LUPULUS L.) 

 RESISTANT TO MILDEW {SPHAEROTHECA 

 HUMULI (DC.) BURR.). 



By E. S. salmon. 



{Mycologist , South-Eastern Agricultural College, Wye, Kent.) 



In certain seasons very severe losses are caused to the hop-crop by 

 the depredations of the mildew Sphaerotheca Humuli (DC.) Burr. 

 Among hop-growers in England this mildew is commonly spoken of 

 as "mould" when it occurs on the leaves or the female inflorescences 

 ("burr") of the hop-plant, and as "red inould" when it attacks the 

 stipular bracts and bracteoles of the strobiles ("hops") (i)^. 



The other serious pest of hop-growing, viz., the "blight" {Phorodoti 

 Humuli Schrank), is satisfactorily held in check by modern methods of 

 washing with an insecticide, but I have frequently been assured by 

 experienced hop-growers that while they feel competent to deal with 

 even prolonged attacks of "bhght," they view with great uneasiness 

 the appearance of "mould" in the hop-garden, especially in dull, damp 

 seasons when sulphuring appears to be of comparatively little use. 



During the past season (1916) the ravages of "red mould" in the 

 hop-gardens in all the hop-growing centres of this country resulted in 

 losses of many thousands of pounds, since some hundreds of acres had 

 to be left unpicked owing to the hops becoming too "mouldy," while 

 in those cases where the attack was slighter, and the hops were picked, 

 the presence of any "mouldy" hops (strobiles) when detected in the 

 sample invariably meant for the grower a serious lowering of their 

 market price. 



Within recent years the hop-mildew has appeared in epidemic form 

 in the "hop-yards" in the United States (2, 3). 



^ For reference to these numbers, see " Literature cited," at end of this article. 



