Diseases of economic plants (1921) Diseases of economic plants diseasesofeconom01stev Year: 1921 150 Diseases of Economic Plants mass of powder nearly the color of iron rust. In early stages of attack these blisters are few and scattered, but they rapidly increase in number. When young, the skin covering the sori is unbroken; later it ruptures, setting loose the rusty, powdery mass of spores beneath. This, the summer stage, is chiefly responsible for the hibernation of rust in the East. Later in the season the sori become black in- stead of rusty-colored, thus constituting the winter stage o
Diseases of economic plants (1921) Diseases of economic plants diseasesofeconom01stev Year: 1921 150 Diseases of Economic Plants mass of powder nearly the color of iron rust. In early stages of attack these blisters are few and scattered, but they rapidly increase in number. When young, the skin covering the sori is unbroken; later it ruptures, setting loose the rusty, powdery mass of spores beneath. This, the summer stage, is chiefly responsible for the hibernation of rust in the East. Later in the season the sori become black in- stead of rusty-colored, thus constituting the winter stage of the rust. In the spring still an- other stage, the spring stage, may occasionally be seen, though it is rare east of the Rocky Mountains. This consists of small, oval, pale spots upon the branches or leaves. In the centers of these spots small round pustules develop in concentric lines. Soon each pustule opens, con- stituting a very minute cup which is sunken into the leaf. From these cups issues a powder quite sim- ilar to that from the sori of the summer stage, though more orange in color. All three stages of rust — spring, summer, and win- ter — may occur simultaneously upon the same plant. The disease spreads rapidly throughout the field during the spring and summer stages. The winter stage is the typical hibernating condition in which the causal fungus may rest un- til the following spring before it can induce further infection. Fig. 79. — Sori ot the asparagus rust upon the stems, enlarged. Original.
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Photo credit: © Bookend / Alamy / Afripics
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