262 



Hop-*' Mould " and its Control. 



[June, 



bourhood of a hop-garden, they constitute a source of danger. 

 As soon as " mould " occurs on these wild hops " — which 

 is often very early in the season — myriads of summer-spores 

 begin to stream from them on the air, and with favouring 

 winds these reach adjacent hop-gardens. Since wild hops " 

 are not sulphured, the mould " on them constitutes an. 

 unchecked source of infection throughout the season; the soil 

 beneath them becomes plentifully contaminated with the con- 

 ceptacles and their winter-spores, accounting for the early out- 

 breaks of " mould " which so often occur year after year on- 

 wild hops." A case of the sudden infection early in the 

 season of a hop-garden at " Spring Grove," Wye, was 

 investigated by Mr. Arthur Amos and the writer. The original 

 source of the outbreak was tracked down to some " mouldy " 

 " wild hops"' growing by the side of a ditch adjoining the hop- 

 garden. Infection of the hop-garden from this point was 

 proceeding through a wedge-shaped area of increasing, 

 dimensions. All " wild hops " in the vicinity of a garden 

 should be grubbed up and destroyed.* 



(7) Varieties Resistant to " Mould." — No exact testing, under 

 the same conditions, of the comparative susceptibility to " mould " 

 of the various commercial varieties of hops appears to have been 

 made. The true " Golding " varieties are generally believed to 

 be specially susceptible, while the old varieties " Grapes " and 

 " Jones " have been stated to be more resistant. It is probable 

 that under certain conditions all the commercial varieties 

 of hops at present grown are liable to bad attacks of " mould." 

 There is, however, one variety of hop which is absolutely immune 

 to the attacks of " mould." This is a variety which possesses 

 yellow-green leaves and is called the "Golden Hop"; it is 

 sold by nurserymen as a garden plant, and does not appear to 

 have any commercial value, since it is of weak growth and the 

 hops are of poor brewing quality. Attempts are being made at 

 Wye College to raise, bv " cross-breeding " from the " Golden 

 Hop," seedlings imnmne to " mould " and possessing the other 

 desirable characteristics. 



* The same species of mildew (S. ffumuli) lives on the cultivated 

 Strawberry and also on a number of common weeds (e.g., Meadow-sweet, 

 Field Lady's-mantle, Willow-hevb, Potentilla repfans). Investigations have 

 shown, however, that the forms of the mildew on all these plants are 

 specialised and cannot pass, e.g.., from the hop-plant to the strawberry, or 

 vice versa. (See E. S. Salmon in Journ. Agric. Sci., II, 327 (1907). there 

 is consequently no danger to the hop-garden from this mildew growing on 

 any other plants — notwithstanding the statement to the contrary that is 

 occasionally met with. 



