Diseases of economic plants (1921) Diseases of economic plants diseasesofecon00stev Year: 1921 332 Diseases of Economic Plants reddish brown tinge. After the leaves have fallen the stem dies and becomes covered with a light pink coating of the spores of the wilt fungus. The spread of the disease is more gradual and less conspicuous in the early part of the season, but after the peas begin to set fruit they succumb rapidly, and a field that in July gave promise of a fine crop may be entirely dead before Septem- ber without having matured a pod. The disease usually appears in spots, like the V
Diseases of economic plants (1921) Diseases of economic plants diseasesofecon00stev Year: 1921 332 Diseases of Economic Plants reddish brown tinge. After the leaves have fallen the stem dies and becomes covered with a light pink coating of the spores of the wilt fungus. The spread of the disease is more gradual and less conspicuous in the early part of the season, but after the peas begin to set fruit they succumb rapidly, and a field that in July gave promise of a fine crop may be entirely dead before Septem- ber without having matured a pod. The disease usually appears in spots, like the VN\ 11 \ if Yf— cotton wilt, and these dis- /j \ // eased areas may spread until a whole field is involved. In moderate cases, or where the varieties planted are less subject to disease, only the weaker plants are killed, while the rest are dwarfed and their yield re- duced. Careful examination of the roots shows that many of the small, lateral roots are dead, small tufts of roots marking the points of infec- tion (Fig. 174). This tufting of the rootlets is similar to that produced on cotton by the cotton-wilt fungus. In all cases the veins of the stem are brown, and the dis- ease may clearly be distinguished by cutting across the stem to observe whether the color of the wood is normal. This discoloration, which may often be seen through the translu- cent stem of the cowpea, is characteristic of this class of diseases. The name 'wilt' is somewhat misleading, since the leaves usually drop off before there is any conspicuous wilting. Fig. 174. — Roots of diseased cow- pea at left; healthy roots on the right. After Orton.
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