.GARDEN PESTS IN NEW ZEALAND 



The amount of carbon-bisulphide to be used varies, according to 

 circumstances. For soil fumigation a special type of "gun" is on the 

 market "for injecting the bisulphide into the soil, but for ordinary garden 

 purposes it is sufficient to make holes in the ground with a stick, pour 

 in the fumigant, and close up the holes. When holes are made about 

 18in. apart, half an ounce of bisulphide to a hole is sufficient, the depth 

 of the hole varying according to the depth of the pest to be controlled. 



For the fumigation of seeds, bulbs, potatoes, etc., an airtight 

 chamber is necessary. This is also of value in the control of pests of 

 potted plants. The dimensions of a chamber will vary acco<rding to the 

 demands made upon it. Carbon-bisulphide gas being heavy, the con- 

 tainers (shallow dishes) should be placed on a shelf near the top of the 

 chamber during fumigation. The proportion of fumigant to the air 

 space varies according to the plants and insects to be fumigated. 



For lawn-infesting insects, carbon-bisulphide can also be used in an 

 emulsion as a spray prepared as follows : Fifty grams of powdered 

 resin are gradually added to 135 cc. of a 7 per cent, solution of sodium 

 hydroxide, previously wanned; 450 cc. of hot water is now added, and 

 the whole agitated until the resin is completely dissolved, when 50 cc. 

 of oleic acid is also added. To prepare the emulsion, three parts of this 

 soap solution are thoroughly agitated with seven parts of carbon- 

 bisulphide until emulsification is complete, which can be gauged by the 

 creamy-white colour and viscosity. For use dilute in the proportions 

 of 18 pints of the emulsion with 50 gallons of water, applying by means 

 of a watering-can or spray-pump at the rate of one gallon to every square 

 foot of lawn. 



Calcium cyanide, on being exposed to the atmosphere, gives off 

 hydrocyanic acid gas, the evolution of the gas being governed by tempera- 

 ture and humidity. Calcium cyanide has replaced the old method of 

 generating the gas by the action of sulphuric acid on potassium cyanide, 

 and is sold in the form of dusts or granules. In the use of this material 

 very great care is necessary, since the gas is highly poisonous, and also 

 scorching of the foliage of plants results if atmospheric conditions are 

 not considered carefully. With ordinary care, however, calcium cyanide 

 can be safely handled. It is extremely effective against all kinds of 

 pests, and can be used to fumigate soil, glass-houses, or as a dust on 

 plants in the open. 



(c) Influence of Natural Enemies. 



As stated in the first chapter, plants are to be looked upon as the 

 primary producers of life (since all animals are directly or indirectly 

 dependent upon them ) , and the animals as the consumers. Many of the 

 latter are destructive to crops grown by man, and become pests, but 

 others, fortunately, exist upon these pests, and are classed as beneficial 

 animals ; it is the purpose of this section to deal with the more important 

 of these from a horticultural viewpoint. In New Zealand such beneficial 

 animals are insects, birds, and the hedgehog. 



Insects. 



There is a wide range of insects that live at the expense of their 

 fellows, and without these plant production would be impossible, either 

 by Nature or by man. These so-called beneficial insects or parasites 

 are the greatest factor in maintaining within reasonable bounds the 



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