During 1914 there was no fruit on any of the trees in this orchard, the fruit buds in the peach orchards of northwestern Arkansas having been killed by low temperatures in January. The experiments of 1915 were conducted in the same orchard as were those of 1914. Plat 1, consisting of 34 trees, was treated with nitrate of soda at the rate of 2 pounds per tree; plat 2, consisting of 24 trees, was treated with nitrate of soda and dried blood at the rate of 1 pounds of the former and 1 pound of the latter per tree. Six trees between these two plats were left untreated and were considered as checks, as was also the remainder of the orchard. Owing to the press of other work, the fertilizers were not applied until May 22. The orchard had been cultivated a week before and was again cultivated on June 1. The trees had bloomed on April 25 and had set a good crop. On June 10 there was very little of the disease on the nitrate plats, but considerable was beginning to show on the untreated plats. The large dark-green leaves of the nitrate plats were in sharp contrast to the relatively pale leaves of the unfertilized plats. By June 30 the contrast was much greater, as the disease had given a ragged appearance to the foliage of the untreated plats, while the nitrate plats remained nearly free from infection. On August 5 the fruit was just beginning to ripen. On certain limbs of the untreated trees there was considerable injury to the fruit, though not enough to be of importance commercially. The fruit of one limb, for instance, would be badly affected, while that of the remainder of the tree would be free from injury. There was almost no injury to the fruit of the nitrate plats. By the end of the season the difference in the appearance of the foliage of the nitrate plats and the untreated ones was as great as during the previous season. The difference between this damage and the total damage caused by the bacterium was about the same on both the fertilized and unfertilized trees as during the previous season. There was no perceptible difference between plats 1 and 2 in so far as the amount of infection was concerned. Eight of the fertilized trees which bordered on the meadow were considerably more affected than the others in the same plats, but were infected much less than the unfertilized trees. During both years the nitrate plats included the trees which during 1913 suffered the heaviest infection. Sixteen of the trees treated with nitrate of soda in 1914 were included in the nitrate plats in 1915. These, however, showed no superiority, in so far as resistance to the disease was concerned, over those which had not received fertilizer during the previous year. In the experimental plats of both 1914 and 1915 the sole difference in the treatment of the plats, including the check plats, was one of fertilization. All had been given the same amount of pruning and cultivation and received throughout the two years exactly the same treatment except as to the fertilization outlined in these experiments. It is evident, therefore, that the striking differences noted were due to the nitrate of soda alone. The larger amount of infection on the trees of all plats growing next to the meadow, upon which the grass was encroaching, indicates that cultivation was generally beneficial to all the plats. Rolfs,' in Missouri, obtained good results in the control of this disease by means of cultivation, pruning, and the use of nitrogenous fertilizers. In those regions of the South in which the disease has been serious, nitrogen appears to be the most deficient of the important plant-food materials.2 These experiments indicate that, at least in the South, peach orchards which are kept in good growing condition are not liable to suffer from the disease to any serious extent. Proper pruning, cultivation, and fertilization so increase the resistance of the trees that the causal organism is unable to attack them successfully. Pruning, besides benefiting the tree in general, may also remove many of the twig cankers in which the bacterium passes the winter, thus eliminating many of the sources of infection. SUMMARY AND CONCLUSIONS. (1) The peach bacterial spot, also known as bacteriosis, caused by Bacterium pruni, occurs in practically all peach-growing regions of the eastern half of the United States. It is most serious in the more southerly parts of this region. Bacterium pruni also causes a disease of the plum, affecting especially the Japanese varieties. (2) Twigs, fruit, and leaves are affected, but the most serious injury is to the leaves. (3) Experiments carried on by the writer and others indicate that the disease may be kept in check in southern peach orchards by proper pruning, cultivation, and especially fertilization. Nitrate of soda was by far the most efficient fertilizer used. Trees in which a high state of vigor and health is maintained are commercially resistant to the disease. 1 Op. cit. * For a discussion of peach tillage and fertilization, see Gould, H. P., Growing peaches: Sites, propagation, planting, tillage, and maintenance of soil fertility, U. S. Dept. Agr., Farmers' Bul. 631, 24 p., 7 fig. 1915. WASHINGTON: GOVERNMENT PRINTING OFFICE: 1917 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 5 CENTS PER COPY |