. Diseases of economic plants. Plant diseases. Drupaceous Fruits 97 PLUM • Black-knot ^^^ (Dibotryon morbosum (Schw.) T. & S.). — The black-knot receives its name from the swollen black distortions, 3-15 cm. long, upon the branches. In a young condition the galls are olivaceous, but as the season advances they become darker and eventually coal black. At the same time soft tissue changes to a hard, brittle texture. When the knot com- pletely encircles the twig, the supply of nourishment to more distant parts is seri- ously interfered with. If less than the whole of the circumference be invo
. Diseases of economic plants. Plant diseases. Drupaceous Fruits 97 PLUM • Black-knot ^^^ (Dibotryon morbosum (Schw.) T. & S.). — The black-knot receives its name from the swollen black distortions, 3-15 cm. long, upon the branches. In a young condition the galls are olivaceous, but as the season advances they become darker and eventually coal black. At the same time soft tissue changes to a hard, brittle texture. When the knot com- pletely encircles the twig, the supply of nourishment to more distant parts is seri- ously interfered with. If less than the whole of the circumference be involved, the dam- age is not so great, but it is even then suf- ficient to seriously im- pair the fruiting of the tree. Black-knot may either kill the tree in a year or two, or sim- ply destroy its value. All varieties of plums, and nearly all cherries, are subject to the dis- ease, which is therefore very widely distributed. It is more common in the East than in the West. It is probable that infection can occur only through injured bark. One step toward lessening the disease is, therefore,. Fig. 49. — Portion of a plum tree badly infested with black-knot. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Stevens, Frank Lincoln, 1871-1934; Hall, John Galentine, 1870-. New York, Macmillan
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Keywords: ., bookauthorstevensf, bookcentury1900, bookdecade1920, bookyear1921
