Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 292 DISEASES OF ECONOMIC PLANTS gradually extend in all directions, involving the whole root. Older spots, 2-5 cm. across, often break or crack irregularly near the center. This decay differs from the soft rot in that the spots are dry and hard and that it is present upon the roots before digging. With the hand lens very small, hairlike, black structures, 1 mm. high, are seen studding the centers of the diseased areas. These are the beaks of the pycnidia of the causal fungus. Upon young sprouts b
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 292 DISEASES OF ECONOMIC PLANTS gradually extend in all directions, involving the whole root. Older spots, 2-5 cm. across, often break or crack irregularly near the center. This decay differs from the soft rot in that the spots are dry and hard and that it is present upon the roots before digging. With the hand lens very small, hairlike, black structures, 1 mm. high, are seen studding the centers of the diseased areas. These are the beaks of the pycnidia of the causal fungus. Upon young sprouts before they are set out the disease causes black, dead patches, especially at the base of the shoot or even upon the young leaves. The wood of the stem may be browned. Such sprouts if set result in enfeebled plants with dis- eased roots. The fungus throws myriads of spores into the soil. This disease thus falls under the general class of soil diseases. In addition to the suggestions given on page 63, especial precau- tion should be exercised to avoid sets already affected. Badly af- fected shoots are easy of recognition, but the closest scrutiny is needed to cull out those only slightly affected. Fig. 127. — Black rot of sweet potato. Original.
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