Page:Popular Science Monthly Volume 42.djvu/664

 644 known for more than a decade; yet, thanks to the remarkable series of investigations and experiments carried on by the Division of Vegetable Pathology of the Department of Agriculture—at first under the direction of Prof. F. Lamson-Scribner, and later that of Mr. B. T. Galloway—assisted to a considerable extent by several of the State experiment stations, their efficacy is already well attested, and they are in practical use over a large territory. The fungicides most commonly employed are the Bordeaux mixture, a combination of copper sulphate, lime, and water; eau céleste, a combination of copper sulphate, ammonia, and water; and various solutions of carbonate of copper. These fungicides are sprayed upon the plant early in the season, before the ingress of the disease-producing fungus, in such a way that after the water evaporates the leaves and stems will be coated with minute particles, usually crystals, of a salt of copper. These tiny sentinels stand guard over the plant; when a fungus spore falls upon the leaf and sends out its germinating tube, the latter comes in contact with the copper crystal and is destroyed.

The fungicide generally used for the downy mildew of grapes is eau céleste. It is first applied in spring, a few days before the vines blossom. One or two, and rarely three, additional applications are afterward made at intervals of about two weeks. In 1890 I made a special investigation of the results of spraying against this disease in northern Ohio, visiting many of the vineyards personally and sending out numerous letters of inquiry. As a result I was able to publish in the Bulletin of the Ohio Experiment Station (Vol. III, page 262) the following paragraph:

"The early part of the season of 1890 was peculiarly favorable to the development of downy mildew, and consequently an excellent opportunity was offered to test the value of eau céleste as a preventive. It has stood the test in a remarkable manner, and the efficiency of the preventive, when properly applied, has been proved beyond question. All accounts agree in this respect, and show that while the crops on the unsprayed vineyards averaged from one half a ton to a ton per acre, the sprayed vineyards yielded two to three tons per acre. Such results need no comment: they speak for themselves."

For many years pear trees, both in the nursery and orchard, have been seriously affected by a fungous disease that causes the leaves to drop during the summer prematurely, sometimes as early as June or July. It also often develops upon the young pears, causing a spotting and cracking of the fruit. The mycelium of this fungus grows between and through the cells of the pear leaf, causing circular brown spots to appear upon the surface; these spots gradually enlarge as the mycelium spreads through the tissues, and, finally, the whole surface being affected, the leaf