. Minnesota plant diseases. Plant diseases. 378 Minnesota Plant Diseases. The powdery mildew or blight of the rose [Sphaerotheca pannosa {Walk.) Lev.]. An enormous amount of damage is sus- tained yearly by the ravages of this blight in gardens and green- houses. The leaves of the attacked rose bushes become covered with a fine white coat of the fungus mycelium and often become distorted or stunted in various ways. The young leaves and buds are especially damaged, and many leaves are killed. The mycelium sends suck- er-like branches into the interior of the epidermal cells of the host and from
. Minnesota plant diseases. Plant diseases. 378 Minnesota Plant Diseases. The powdery mildew or blight of the rose [Sphaerotheca pannosa {Walk.) Lev.]. An enormous amount of damage is sus- tained yearly by the ravages of this blight in gardens and green- houses. The leaves of the attacked rose bushes become covered with a fine white coat of the fungus mycelium and often become distorted or stunted in various ways. The young leaves and buds are especially damaged, and many leaves are killed. The mycelium sends suck- er-like branches into the interior of the epidermal cells of the host and from these draws its nourish- ment. This of course re- sults in a drain upon the host plant. During the summer erect threads are produced on the surface of the leaves and these, form chains of spores, which are carried about by the wind and rapidly spread the disease from leaf to leaf and from plant to plant. These summer spores, therefore, act in a manner similar to those of the wheat rust. Toward late summer and fall small black bodies about the size of a pin-point are formed on the mycelium, and these are the closed sac-capsules. They are yellowish-white, when im- mature, becoming black when mature; they are attached to the mycelium by special brownish appendages. TTiey have a more or less membranous wall, which is divided into polygonal areas. The sac-capsule, when broken, shows a single, spherical, colorless sac, in which are found eight oval spores. The sac-capsule does not open until spring, when the wall decays, setting the spores free. These spores, therefore, function as winter spores. In the spring they germinate, by sending out a fine tube, which again. Fig. 203.—Powdery mildew of roses. A leaf of a rose attacked by the disease. After 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 Freeman
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplantdi, bookyear1905
