GARDEN SANITATION.--Clean gardening is an extremely important control factor. In most gardens there are rank growths of grass and weeds in out-of-the-way places, along boundaries, and bordering cultivated plots. Such growths, especially when the weeds are related to the garden plants, are always favourite breeding places for many pests that move on to cultivated plants immediately they appear above ground. If these growths are cut and burned in the winter, and the ground thoroughly dug, many a spring infestation will be suppressed by the control of hibernating pests; it is the control of spring infestations that will save a great deal of trouble throughout the summer and autumn. The compost heap, where garden refuse is dumped until sufficiently rotted, may be a source of infestation; not only does it attract and breed many destructive underground pests, but it may be infested with the spores of diseases harboured by the plant refuse of which it is composed; it is thus a ready means of reinfesting the soil. Diseased and pest-infested refuse should be burned without delay, and only healthy refuse used for the compost heap if not dug into the ground, where it will rot. CROP ROTATION.--Growing the one type of crop on the same piece of ground for several seasons encourages the development of pests and diseases; but by a rotation of different kinds of plants the continuity of the conditions favourable for the pests and diseases is broken, and the latter do not have the chance of becoming thoroughly established. DISEASES SPREAD BY PESTS.--It should be borne in mind that the fewer the animal pests, the less chance there is for diseases to spread. It is now well known that many pests, though not necessarily epidemic themselves, are carriers from plant to plant of certain destructive fungous, bacterial and virus diseases. 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.