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Insects - Diseases and Spraying

plants, trees, fungi, copper and compounds

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ThE rise of spraying. The spraying of plants is a wholesale method of destroying insects and fungi. It is one of the great discoveries of the nineteenth century. Though the whole subject is less than twenty-five years old, already a whole book has been devoted to it, and Experiment Station bulletins without number have been published. About twenty-five years ago the downy mildew of the grape crossed the ocean front America and ravaged the vineyards of France. A few years later it was acci dentally discovered that copper compounds would destroy this fungus. Prior to this time no wholesale method of destroying insects or fungi was ever conceived of. Against each insect and each disease there was a special formula. ln some cases dozens of remedies were proposed and many of them were preposterous. The subject was infinitely compli cated, like the subject of medicine. We now know that the principles of spraying are very simple, and can be easily fixed in the mind. In fact, they can be stated in two short paragraphs.

The Destruction of Insects. Insects that feed upon plants fall natu rally into two classes: those that chew and those that suck. Chewiny insects are killed by poisoning their food. Paris green is the typical remedy for chewing insects. It is dissolved in water and sprayed upon the foliage, flowers and fruit. London purple and arsenate of lead are also much used. It is the arsenic in these compounds which poisons the insects. ,S'Iwkiny insects, as the aphids and all other true bugs, probe below the surface and draw out the juices of plants. The poisoning of their food by spraying is therefore impossible. These insects are destroyed by spraying upon their bodies soapy and oily solutions. The alkali of the soaps injures the delicate body wall, and the oil suffocates the insects by stopping their breathing pores. Kerosene-and-soap emulsions are specifics for the destruction of sucking insects. 11(wifly ifleets, such as make winding in solid wo(al, or under bark, are sometimes a serious injury to trees. The locust borer renders that tree unlit for lumber.

Peach, pear and apple trees often break off at the ground, showing their wood to be honey-conthed by borers. Sprays and washes may do some good in keeping the adult insects lay the eggs. But for the irub that does the boring is so effective as a flexible wire thrust into the burrow, that surprises the miller at his toil and destroys him without mercy. A bunch of sawdust. or an ex udation of was or gum llF;nally indicates the entrance to the burrow. The bases of fruit trees should be examined care fully at least twice a year and the borers dug out.

The Destefletion, of Friuli. Coplie: compounds are deadly to all germinat ing spores of fungi., It is said that ono part of copper sulphate in ten thousand parts of water will prevent the germina tion of the spores of apple seal), pear leaf blight and other fungi. Bordeaux mixture is the standard remedy for fungous diseases of plants. It is made of copper sulphate diluted with milk of lime and water. The lime merely keeps the copper sulphate from burning the foliage. Fungi that attack the external parts of the plant, as dOW111" mildew of the grape, are easily reached by spraying. Those that live within the tissues. as the anthracnose of the raspberry, ,tre invulnerable once they become estaldished. ']'heir spores must be killed by contact with Bordeaux mixture sprayed upon the surfaces on wlfich they lodge.

Combotioy Othcr Discos( s. Mints are often victims of diseases caused by bacteria, which are commonly confused with though they are quite distinct. The •' fire blight " of pear trees. which suddenly causes the leaves and twigs to turn brown and become shrivelled, is caused by a bacterium which enters through the growing tips and develops the stems. There is 110 remedy for bacterial diseases of plants. The affected trees should he primed, and the diseased portions burned.

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