Some of the principal diseases of the plum are also common to the cherry or the peach, or both. Plum-pockets (Exoascus pruni) is a specific plum malady. Shortly after the blossoms fall the little plums swell rapidly to an inch long or more and become bladdery. As the disease progresses the light green color changes to deep brown or black, the walls thicken, the stone fails to develop and the fruit falls. Af fected foliage and green twigs also become dis torted. Spraying before the buds open and again after the flowers fall is recommended as a check. (See FUNGICIDE). Black, or plum knot (Plowrightia morbosa) is common to both plums and cherries. Swellings appear upon the twigs and branches, burst and reveal a golden brown or yellow interior with velvety appear ance due to the rapidly forming summer spores. As the season advances the surfaces change to black with a more or less pimply appearance. In the spring a second crop of spores (winter spores) is liberated. Under favorable condi tions spores from either crop may spread the affection through crevices in the bark, etc. The knots are perennial, gradually extending the infested area Cutting and burning as soon as discovered; painting the wounds with kero sene or Bordeaux mixture, thorough spraying with standard Bordeaux mixture before the buds open and with dilated mixture afterward are all recommended and should all he practised. One alone is insufficient. Badly infested trees and trees of wild cherries, plums, etc., should be burned promptly. Leaf blight or shot-hole fungus is produced by two species of fungi, Septoria cerasina and Cylindrosporium pads. Small purplish spots upon the leaves gradually turn brown and drop out leaving shot-like holes. If badly infested the leaves turn yellow and fall, sometimes defoliating the trees. Spraying with diluted Bordeaux mixture at intervals of two weeks from the time the leaves expand until midsummer is considered a specific. This dis ease is often found on cherries. Systematic annual spraying will hold all these diseases in check.
Comparatively few insects feed upon the plum. Some caterpillars and other leaf-chewing insects sometimes appear in devastating num bers, but they can usually be controlled with Paris green (lime should be added to prevent injuring the foliage) • plant lice are sometimes troublesome, but whale-oil soap, kerosene emul sion, etc., are effective. (See INsEcrictne). But
the most serious enemy is the plum curculio (Conotrachelus nenuphar), which in many sec tions has completely destroyed the crop. The adults, small gray-black snout beetles less than a quarter of an inch long, appear in spring and until the fruit has formed feed upon the foliage. Then the females chew little crescent-shaped cavities in the young plums, and lay their eggs in holes bored beside the crescent or in the crescent itself. The white, footless larva bur row to the region of the stone where they live for about three weeks. The fruits fail to de velop and fall, and the larva burrow into the ground where they pupate for about four weeks, emerging as adults which hibernate. They have only one brood. Before the trees blossom arsenitcs may be used; but jarring the adults into sheets in the early morning while they are torpid and dropping them into kerosene is most practised. Special machines like inverted umbrellas on wheels are in use in large plum orchards. The plum gouger (Coccotorus scutel laris) is a troublesome pest in the Mississippi River basin. Its habits are much like those of the curculio. It does not, however, make a crescent-like mark, and its larva feed in the stone instead of around it.
Bartrum, E., 'Book of Pears and Plums' (New York 1903) ; Hedrick, W. P., 'Plums of New York) (Albany 1911) ; Waugh, F. A., 'Plums and Plum Culture' Fork ork 1901; this work contains a bibli ography) ; Saunders, 'Insects Injurious to Fruits' (Philadelphia 1889) ; Smith, 'Manual of Economic (Philadelphia 1896). The following Agricultural Experiment Sta tions have published bulletins upon plums: Vermont, Nos. 53, 67 and 75, with references for 1896-1901; Wisconsin, Nos. 63 and 87; Cornell University, Nos. 38, 62, 106, 131, 139 and 175; United States Department of Agri culture, Bulletin No. 172, contains by Wight, W. F., 'Varieties of Plums derived from native American Species' (Washington 1915).