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In the control of diseases Nature plays a very big part by means of birds, insects, sunshine, and water; but, especially under circumstances of intensive cultivation, we find it necessary to supplement these measures by applying chemicals. Many preparations have been mentioned-they are but a small percentage of those offered for sale. These compounds act in varying ways, and accordingly may be classified as fungicides, ovicides, contact poisons, and stomach poisons. They are used as dusts in powder form, or as liquid sprays in solutions or emulsions. In general, sprays are more effective than dusts.

There are many manufacturers marketing sprays and dusts; each firm sells its products under proprietary names. Often similar products are sold under quite dissimilar names, and occasionally the one firm will sell one product under different names in each of several countries. These practices are very misleading, especially when, in addition, each preparation is alleged to be a panacea for a multitude of garden diseases. Many of these claims have some justification, but usually each spray or dust has one main use. It may give some slight assistance in controlling other diseases, but is almost always inferior to other types available for those purposes.

Every garden has its pests and diseases, and garden equipment is not complete without some type of spraying apparatus and at least some of the more commonly needed chemical preparations. A stirrup pump or a knapsack spray is necessary in all but the very small gardens. Most sprays tend to run off foliage unless a "spreader" is added. Several are described later.

In the following pages an attempt is made to explain, and to reduce to as small a number as possible, the recommended sprays and dusts, while maintaining efficient control of diseases.

Our most important fungicides are preparations of TMTD, copper, sulphur, and white-oil emulsions. Copper and sulphur act on the young mycelium of the fungus as it emerges from the spore. White-oil emulsions act on the more mature fungus, as well as on the young stage. The preparations of TMTD (tetramethyl thiuram disulphide) have been in use in Australia for only a few years; the best known of them are Thiotox, and TMTD Fungicide. They combine the effects of copper and sulphur on fungi, and represent one of the greatest modern advances in the control of plant diseases.

Thiotox contains eighty per cent of TMTD, and at the concentrations recommended by the manufacturers it is harmless to foliage. On the contrary, the foliage of plants that have been sprayed several times with Thiotox assumes a noticeably healthy dark-green colour. The powder, being insoluble, is applied as a suspension, but leaves very little disfiguring deposit on the plants. If it is used every ten to fourteen days black spot, mildew, and rose rust will be kept out of any rose garden, and the consequent difference in the vigour of the plants and the general appearance of the garden is quite amazing. It clearly demonstrates the value of the maintenance of health in the foliage, and this had not been possible with earlier sprays. It is compatible with Chlorparacide and the gamma isomer of BHC (Lindane), but not with DDT. By adding Lindane to Thiotox one can control all the fungus diseases, aphis, thrips, and caterpillars with the one mixture. It is incompatible with copper compounds, but this combination is unnecessary.

Bordeaux mixture, Bordinette, and Cuprox are the best of the copper fungicides. Their main use is in black-spot control, and, as already stated, they are superseded by Thiotox. Because the fungus of black spot is inside the leaves it is inaccessible, and so all of these sprays, including Thiotox, are used to prevent black spot infection, or the spreading of it if already present, because cure of the infection is impossible. It is better to apply sprays before rain than after it, for rain scatters the spores. The copper sprays are apt to cause scorching of foliage if used on very hot days.