Co-operation.—In a locality of many gardens a co-operative spirit is essential, since a single neglected garden in an otherwise well-managed locality will be responsible for discounting the labours of the neighbours.
(b) Use of Chemicals.
Chemicals are essential in the control of pests and diseases, and are applied either in the form of sprays or dusts. The former method is the more usual in this country, but where the water supply is poor dusts tend to take the place of sprays. Chemicals used for horticultural purposes are of two distinct kinds—those for the control of animal pests 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 possessed 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. Fumigants 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, 3lb. of paste, or 1½lb. 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.