154 



Hop-'' Mould " and its Control. 



[May, 



Everything possible should be done, therefore, to help the hop plant to 

 pass through as quickly as possible the critical stage when it is in "burr." 

 If no pollen-dust from a male hop reaches the brush," the hop remains 

 in burr some 10 days longer than when pollen has been supplied, and 

 then sets into a seedless hop, whereas if pollen reaches the brush, the 

 " burr " stage passes quickly, and a large seeded hop is produced. It is 

 consequently a wise precaution — as Mr. A. Howard first pointed out* — to 

 plant a certain number of male hills in the hop-garden, more especially as 

 it has now been conclusively proved that fertilisation of the " burr " is 

 essential for the production of well-grown-out hops.f 



(c) To (he Hop. — Serious injury is very commonly inflicted by 

 il mould " on the hop-cone in all stages of its development. All kinds 

 of malformations of the cone may be met with ; a very young hop 

 may be entirely converted into a white " mouldy " knob, or the young- 

 cone may be "eaten into " on one side, or at the base or at the tip; 

 or hops may occur which are normal in shape and size and yet diseased 

 to the extent that many of its "petals" bear the conceptacles of the 

 mildew. It is among the ripening hops that the condition so well known 

 as " red mould " is met with. " Eed mould " was long thought to be 

 due either to the effect of certain atmospheric conditions (hot sun, mist, 

 &c), or to the attacks of some special parasite on the hop-cones, but it is 

 now definitely established that "red mould" is nothing more nor less 

 than white " mould," and the one can change into the other according to 

 the part of the hop plant that is attacked. The name " red mould " is 

 given to it on the ripening hop-cones, because under the attacks of 

 the mildew the " petals " turn a foxy- or reddish-brovm colour ; very little 

 " spawn" and few summer-spores are formed, hence the mildew does not 

 become white nor resemble the " mould " elsewhere, but conceptacles with 

 winter-spores are produced abundantly. It is one of the most insidious 

 forms of the disease, and can only be dealt with by the rigorous sup- 

 pression earlier in the season of all outbreaks of white " mould." J 



Preventive Measures. — Direct. — ' ' Flowers of sulphur ' ' (pure, 

 sublimed sulphur) is the great specific against " mould," as 

 all hop growers know. It should be applied much earlier in 

 c the season than is generally done. Owing to the fact that 

 winter-spores arise from the soil during May, the first out- 

 breaks of white " mould " for the season usually take place 

 (unknown to the farmer) during that month. A good knap- 

 sack sulphurator should be employed to apply the sulphur to 

 the leaves of the bines; the under surfaces of the leaves (which 

 are usually infected first) should be well dusted over and a 



* Journ. S.E. Aqric. Coll., XIV. p. 211 (1905). 

 f Journ, Hoard of Agrie., XX, 953 (1914). 



% Last season (1920) reports were received of the prevalence of " red mould " in 

 the hops of only those hills in the proximity of male hops ("seeders"). It seems 

 probable, however, that in these cases there was no mould at all, but that the 

 "going off" in colour (that was mistaken for "red mould") was due to the 

 presence of partially over-ripe cones. Hops will not uncommonly show some of 

 the "petals" which "carry no "seed" at the base still of a bright colour, while 

 those that are "seeded " have turned dark reddish-brown. 



