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COMBINED SPRAYS FOR CONTROLLING INSECT PESTS. 
blight and other fungi, there appears to be a degree of atmospheric 
humidity, which is most favorable to the maximum speed of insect 
metabolism, and this optimun humidity varies for each species, and for 
each stage of each species. ih 
The Chemical factors producing disease relate especially to ‘the 
composition of the soil from which the plant draws many of its require- 
ments for life, and growth and reproduction. Poisonous gases inthe 
air, however, frequently cause great destruction of plant life. This is 
well shown in the neighbourhood of large smelting works, of which 
there are many examples within the Commonwealth—notably the sul- 
phide works at Cockle Creek, New South Wales. The use of certain 
chemicals in the soil has often an important influence on the suscepti- 
bility of plants to disease, and the effects of traces of many substances, 
such as “ Manganese and Fluorides,’ have been investigated. It is 
generally well known to orchardists and others that a fertilizer like 
sodium nitrate will often promote a leafy growth, but that suscepti- 
bility to disease may be increased. Sulphur has been commonly used 
both as a disinfectant and a fungicide, as in potato scab. Thus the 
selection of the right kind of manure is of great importance in attempts 
to combat diseases. 
Parasitic factors—Although it may appear that there are many 
points of resemblance in the methods of attack by insects and fungi, 
closer investigation has revealed many important differences, of which 
an accurate knowledge is essential before we can hope to devise any 
successful methods of control. There is usually some period or stage 
in the existence of parasites (insect or plant) when they are most sus- 
ceptible to attack, and we must study their whole life history and take 
advantage of the information thus gained. This becomes the more 
obvious when it is found that, during a considerable part of the life of 
most insects and fungi, these are either very resistant to any destructive 
agents, or they are inaccessible, being securely buried in the tissues, or 
hidden away, or in some manner protected from attack. We have 
further to remember when devising remedies against the parasites 
attacking plants, that the latter also consist of living cells somewhat 
similar to those of the parasites which we hope to destroy. It follows 
from this that two of the factors that determine the effectiveness of the 
remedial substance are—(1) that it must be capable of destroying the 
fungus or the insect when it comes in contact with it, and (2) it 
must not be injurious to the tissues of the host plant. hese require- 
ments restrict the choice of such fungicides and insecticides, and a 
further limitation arises in the selection of certain spraying and dusting 
materials when other factors which determine the efficiency of this 
method are also taken into account. These factors are—(3) that the 
“spray” must adhere after its application so that it is not removed by 
the first light rain that occurs, and (4) that the “ spray ” must retain 
its effectiveness after drying on the plant. These latter apply more 
particularly to preventive sprays against fungi and poisonous sprays 
against biting insects. In fruit-growing, spraying is now regarded as 
essential to the production of clean, healthy fruit and good crops. It 
is an insurance which it is not wise to neglect. A control seemingly 
unprofitable from the money stand-point for one particular year may - 
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