GARDEN PESTS IN NEW ZEALAND 



and those for- the control of diseases. The commercial horticulturist, 

 however, finds it necessary to apply both in the one spray or dust for 

 the dual purpose of controlling both pests and diseases. As the present 

 work is concerned with the pests, and not diseases, only those types of 

 chemicals for the control of the former will be referred to. 



Sprays and dusts are of three kinds, and act upon pests accordingly : 

 they are either stomach poisons, or act externally on the animal by 

 actual contact and corrosion, or cause death by fumigation. The kind 

 used is governed by the feeding habits of the pest; if the latter is pos- 

 sessed of jaws (woodlice, caterpillars, beetles, etc.), and feeds by. 

 chewing the plant tissues, then a stomach poison is applied and is 

 swallowed with the food ; if the food is the nutrient sap of plants, and so 

 could not be poisoned, a spray acting by contact is used, as against such 

 animals as aphids (green fly), scale insects, etc., in which the mouth- 

 parts are not adapted for chewing, but for puncturing plant tissues to 

 feed on the sap, much the same as a mosquito punctures one's skin and 

 sucks the blood. Fnmigants can be used against both the chewing and 

 sucking pests, the fumes passing into the breathing system. 



STOMACH POISONS. The chief of these are arsenate of lead and 

 Paris green, though the latter has practically gone out of use. Arsenate 

 of lead is sold as a paste and as a powder, and is mixed with water to 

 form a spray, 31b. of paste, or 1-Jlb. of powder, to 100 gallons of water 

 being the proportions used. For garden purposes, smaller quantities 

 must be kept to this strength. 



CONTACTS. - The chemicals used in contact control are red oil, 

 kerosene and lime-sulphur, but all are also fumigants, lime-sulphur 

 being also a stomach poison to a limited extent, though best known as 

 a fungicide. Commercial red oils can be purchased ready for mixing 

 with water without the necessity of emulsification, and the strength at 

 which each brand should be used is given by the manufacturers. Though 

 red oils have mostly replaced kerosene emulsion, many horticulturists 

 still prefer the latter. It is prepared by dissolving 8oz. of soap in one 

 gallon of hot water, and then adding two gallons of kerosene, stirring 

 briskly until emulsification is complete. This is the stock emulsion, and 

 must be diluted before use, the strengths being one part to six of water 

 for use in the winter, and one part to fifteen of water for use in the 

 growing season. Commercial brands of concentrated lime-sulphur are 

 on the market, and the manufacturers' directions for their dilution 

 should be followed. 



FUMIGANTS. - - The chief fumigants are black-leaf 40, carbon- 

 bisulphide and calcium cyanide. 



Black-leaf 40, in which nicotine sulphate is the effective principle, 

 is the most useful fumigant on the market, and acts as a most effective 

 control for sap-sucking, and even some chewing pests. The strength at 

 which this fumigant is used is one part in 800 parts of water, and is 

 applied as a spray. 



Carbon-bisulphide is a liquid, the gas evolved from it being an 

 effective fumigant. It is not used as a spray unless emulsified, its chief 

 use in horticulture being for the fumigation of the soil, glass-houses, 

 stored seeds and vegetables, and imported plants. It is very inflammable 

 and extremely volatile, especially under higher temperatures, the heavy 

 gas being highly explosive when mixed with air. 



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