Elementary principles of agriculture; a Elementary principles of agriculture; a text book for the common schools . elementaryprinci00ferg Year: 1908 162 Elementary Principles of Agriculture be killed by spraying the leaves with poisons. Others, like the sucking insects, may be killed by spraying directly onto the insect some substance that kills by contact, such as oils, alkah washes, etc. The poison must not be strong enough to injure the plants. In some cases, the insects may be killed by treating the plants with poisonous fumes or gases, such as tobacco smoke, 1 ig lUJ ,^pia>iiig. an
Elementary principles of agriculture; a Elementary principles of agriculture; a text book for the common schools . elementaryprinci00ferg Year: 1908 162 Elementary Principles of Agriculture be killed by spraying the leaves with poisons. Others, like the sucking insects, may be killed by spraying directly onto the insect some substance that kills by contact, such as oils, alkah washes, etc. The poison must not be strong enough to injure the plants. In some cases, the insects may be killed by treating the plants with poisonous fumes or gases, such as tobacco smoke, 1 ig lUJ ,^pia>iiig. and the deadly hydrocyanic acid gas, used especially for San Jose scale. Where plants are sprayed to prevent fungous diseases, the poison for insects may be applied in the same solution at the same time. There are many kinds of special machines for applying fungicides and insecticides. They are fully described in special books and bulletins. 232. Classification of Insecticides. Substances that are used to poison insects are called insecticides. There
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