Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 TREES AND TIMBER 447 the spores. This is the cluster-cup stage of a rust which appears later in the season upon goldenrods and asters. Red rot1 (Polyporus ponderosus von Schrenk).— Upon dead trees this rot starts just under the bark, usually near the tree top, often fol- lowing ' bluing.' The wood is at first wet and soggy, but soon becomes brittle, so that it crumbles readily. The cracks become filled with felted fungous threads. The sporophores first appear as fleshy knots, soon red, which wide
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 TREES AND TIMBER 447 the spores. This is the cluster-cup stage of a rust which appears later in the season upon goldenrods and asters. Red rot1 (Polyporus ponderosus von Schrenk).— Upon dead trees this rot starts just under the bark, usually near the tree top, often fol- lowing ' bluing.' The wood is at first wet and soggy, but soon becomes brittle, so that it crumbles readily. The cracks become filled with felted fungous threads. The sporophores first appear as fleshy knots, soon red, which widen to pore-bearing shelves. Cladosporiose blight (Cladosporium herbarum (Pers.) Link). — The ter- minal leaflets die and curl and the tip of the stem is killed. Dark patches of hyphse appear upon the dead parts. POPLAR Rust (Melampsora populina (Jcq.) Lev.).—This is similar to willow rust. See p. 450. Powdery mildew, uncinulose. See willow. Leaf blight, marsoniose (Marsonia Populi (Lib.) Sacc). — Primary in- fection occurs upon the leaves, re- sulting in small, 3-8 mm., circular, black dead spots which are quite definitely bordered. As the leaves die, patches 1 von Schrenk, H., Dept. Agr. Bur. Plant Indus. Bui. 36, 1903. Fig. 194. — Pine needle bearing cluster cup of rust, enlarged. After Clinton.
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