SCIENCE AND INDUSTRY. 
Combined Sprays for Controlling Insect 
Pests and Fungous Diseases. 
By EWEN MACKINNON, B.A., B.Sc. 
Plants, like man and other animals, on account of their living cellular 
structure, are liable to disturbances of the normal functions of the cells. 
The cause of these disturbances or diseases may be due to physical, 
chemical, or parasitie elements. Physical causes depend largely. on 
climate and seasons. ‘Heat, cold, drought, excessive moisture in the 
air or soil, excessive or diminished sunlight, are factors which greatly 
influence plant growth. When one or more of these factors act un- 
favorably, the vitality and resistance of the plant is generally lowered 
and becomes a predisposing cause of attack. Many fungi are only able 
to attack plants that are in an unhealthy condition, and many are 
known as wound fungi and others as facultative parasite, e.g., the fungus 
Alternaria solani (E. & M.) is most generally stated to be the 
cause of “black spot” on the tomato. It is only secondary; how- 
ever, and attacks this fruit commonly towards the flower end, ‘owing to 
the weakening of the tissues there through excessive or diminished 
supply of water to the roots. In experimental infection experiments it 
has been found that uninjured healthy tissues do not become infected. 
Weather conditions have a very important influence on the prevalence 
of disease. The brown rot (Sclerotinia fructigena) of stone fruits has 
often been most destructive during warm moist springs and almost 
absent during similar dry periods. The year 1914-15 was a good 
example, when destruction was very heavy in New South Wales, where 
rainfall was 7.8 inches above normal for the spring and summer 
(August-January), whereas the previous year 1913-14 had a dry 
summer, 13.4 inches below normal, and very little brown rot. Late 
(or Irish) blight of potatoes (Phytophthora infestans), which is 
entirely dependent on-a- sufficient supply of moisture for its rapid 
development, may be thoroughly checked by a hot, drying wind, such 
as a westerly in New South Wales in the summer. Temperature is of 
less importance than moisture in the case of blight, as the conidia will 
readily germinate between the temperatures of 50 deg. and 77 deg. F., 
while the mycelium will continue to grow until the temperature reaches 
88 deg. I°., provided the moisture is sufficient in all cases. = 
As regards the effects of weather on insect, attack, it isa fact very 
often observed by growers, that aphid attacks frequently coincide 
with moist air conditions, whereas red spiders and most Species of 
thrips are more abundant, and hence more injurious during warm, dry 
conditions. The codling moth is a good example of a well-known 
destructive insect whose development is greatly influenced by weather 
conditions, The rate of its development, the time of emergence of 
broods, the number of broods, &c., are influenced by latitude, early and 
late, cool and warm, and wet and dry seasons. As in the case of potato 
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