86 
only to begin active growth with the production of spores, 
when the conditions are once more favourable. In this 
way the disease survives in greenhouses from one season 
to the next, and once a house is infected the disease is 
almost certain to recur year after year unless precautions 
are taken to thoroughly disinfect the soil and all parts of 
the house. 
The practice of disinfecting greenhouses with burning 
sulphur is largely employed in some districts. Whilst 
this is an excellent preventative of insect pests and 
of certain mildews, it 1s useless against the Leaf-Blotch 
of cucumbers. The writer recently established this with 
certainty. A large house which had been badly infected 
with the disease was cleared out and thoroughly disin- 
fected with burning sulphur. A few fragments of 
diseased leaves and fruits were then collected from the 
soil of this greenhouse and brought into the laboratory. 
Spores of the Cercospora, taken from this material, ger- 
minated in water in a few hours and cultures of the fungus 
were readily obtained on suitable media. From this 
experiment it is clear that the spores and resting filaments 
of Cercospora melonis remain uninjured in houses dis- 
infected by burning sulphur alone. Probably more certain 
results would be obtained by spraying the house 
thoroughly, and also drenching the soil with Formalin 
(1 pint per 20 galls.of water). ‘The Board of Agriculture * 
-recommends the use of Jeyes fluid (1 oz. per gall. of water) 
for this purpose, but the writer has no experience of this 
as a disinfectant against parasitic fungi. Needless to say 
all diseased material should be destroyed by burning. It 
is possible to control this disease to some extent by spray- 
ing with Liver of Sulphur (potassium sulphide) two ounces 
in three gallons of water, to which two ounces of soft soap. 
is added to facilitate the sticking of the solution to the 
leaves, which should be thoroughly wetted by the spray. 
The disease is only prevalent where cucumbers are forced 
under glass, but if the ventilation is carefully regulated 
much can be done to reduce the possibility of an epidemic. 
A most effective way of combating it is by growing 
disease-resisting varieties of the cucumber, of which there 
are a number on the market. The most reliable of these 
have rather coarse, hard foliage, but unfortunately the 
* Leaflet No. 76. 
