152 



Hop-" Mould " and its Control 



[May. 



As each of the two million odd spores produced in a large patch 

 of ki mould " is able to propagate in this way, it is no wonder 

 that the hop-grower, unless the earliest patches are dealt with, 

 is often faced with sudden outbreaks of ' ' mould ' ' on an epi- 

 demic scale. The explanation of the efficacy of early sulphuring 

 lies in the fact that the first powdery patches of mould formed in 

 the season are killed before they have time to start hundreds of 

 fresh infections in the neighbourhood. 



So long as the hop-plant continues to produce fresh sappy 

 growth, such as young leaves, lateral shoots, " runners," and 

 the " burr " stage or young hop-cones, the mildew continues to 

 produce its summer-spores. These spores, however, are quite 

 unable to survive the winter months, when the hop-plant dies to 

 the ground. It is important for the farmer to understand in 

 what form and also where the "mould " survives from year to 

 year, since ignorance on these points leads in many cases to the 

 adoption of useless and expensive measures. 



The stage in which the fungus passes the winter is far less 

 noticeable than the white " mould." It can readily be seen 

 with a pocket-len^, however. If during late summer the 



mould " on the lower leaves is examined, minute round 

 blackish-brown bodies (conceptacles) will be observed, usually 

 densely clustered on the " spawn " (Fig. 5). Each conceptacle 

 (perithecium) contains within it a transparent sac (ascus) holding 

 8 winter-spores (ascospores). These conceptacles are also found 

 plentifully on " mouldy " hops. If a hop with " mould " or 

 " red mould " is picked to pieces, hundreds of these dark, round 

 bodies can be seen (with a pocket-lens) on the surface of the 

 " petals " (bracts and bracteoles^ (Fig. 6\. 



When the leaves decay, or when " mouldy " hops are left 

 unpicked and allowed to blow away, the conceptacles with their 

 winter-spores reach the soil of the hop-garden and remain there 

 in security through the winter-months. The following spring — 

 usually in May — these winter-spores are liberated in the follow- 

 ing manner. Each conceptacle — when the weather conditions 

 are right — absorbs water, swells and cracks open, exposing to 

 view the inner sac (Fig. 8). The sac then likewise absorbs water 

 and swells up. expanding like the envelope of a balloon (Fig. 8), 

 until the tension on the expanding wall is so great that the sac 

 bursts and the winter-spores are expelled forcibly through a 

 slit into the air (Fig. 8). When thus liberated the winter-spores 

 are wafted about by air-currents and some get carried to a hop- 

 leaf — usually the lower leaves on the bine. The winter-spore 



