REFLECTIONS ON DISEASE TREATMENT 187 
The Effect of the Spray on the Plant 
One of the properties connected with a satisfactory 
fungicide is that it shall be of a composition and strength 
which will be non-injurious to the plant to which it is 
applied. This, however, cannot always be determined 
precisely, for under different meteorological conditions 
the injurious action of a fungicide may vary considerably. 
Bordeaux Mixture may be perfectly harmless to apple 
foliage under one set of conditions and ruinous to it under 
different conditions. Generally, the atmospheric con- 
ditions of glasshouse cultivation are unfavourable to 
fungicidal treatment, and special precautions are neces- 
sary to prevent undue damage to the plants. Too strong 
a fungicide, or one applied under unfavourable conditions, 
produces damage to the foliage, which may vary from a 
slight scorching of the tender shoots to the entire 
destruction of the leaves and the defoliation of the plant. 
In order to reduce to a minimum the possible harmful 
effects under glass due observation must be paid to the 
following rules: 
(1) In the absence of expert advice or previous 
experience no new fungicide should be applied to the 
main body of plants in a house before a preliminary test 
has been made upon a small number. 
(2) Spraying should be done in the cool of the evening, 
and never before the sun has ceased to shine directly on 
the houses or whilst the temperature is above 70° F. 
(3) After spraying with copper compounds the foliage 
should be kept as dry as possible, as surface moisture 
increases the amount of scorching. : 
(4) Before spraying cucumber plants with liver of 
sulphur, lime sulphur, or ammonium polysulphide, care 
should be taken to see that the houses are sufficiently 
shaded, otherwise scorching will result. The morning 
after spraying with these compounds the ventilators 
should be opened to allow the escape of the hydrogen 
sulphide given off from the fungicidal compounds. 
