390 Diseases of Economic Plants 



Rust (Melampsorella elatina (A. & S.) Arth, JEcidium). — 

 This cluster-cup fungus produces bushy distortions, "witches' 

 brooms," by causing profuse branching of the affected part 

 of the tree. These abnormal branches soon lose their leaves, 

 and cluster-cups are produced upon them. The brooms are 

 perennial and increase in size each year, in some cases largely 

 covering a whole tree with the brooms. In such cases the 

 trees are stunted and may even be killed. Infection may 

 be reduced by destroying the spore-bearing branches or by 

 eliminating the alternate hosts, Alsine and Cerastium. 



Canker (Dasyscypha resinaria (C. & P.) Rehm). — Swollen 

 cankers occur in the stems and branches, even girdling the 

 main trunk and killing the tree. After the branch is dead the 

 causal fungus produces spores in small disks, orange-colored 

 within, about 4-6 mm. wide and high. 



HORSE-CHESTNUT, BUCKEYE 



Leaf-blotch '*^'- {Guignardia a'sculi (Pk.) Stew., Phyllostida) . 

 — Unsightly spots upon the leaflets, and premature defolia- 

 tion, render this the most conspicuous disease of this tree. 

 The brown spots are at first circular, but as they enlarge 

 are limited by the larger ribs, thus becoming nearly rect- 

 angular. Pycnidia may be seen by means of a lens. This 

 is a decided nursery pest and is also troublesome on park 

 plantings. 



Lime-sulfur or Bordeaux mixture have much reduced 

 the spotting. Dusting (sulfur, 90 parts, arsenate of lead, 10 

 parts) has also proved effective. 



LARCH 



Mistletoe ^^^ (Razoumofskya) . — This is the chief enemy 

 of the western larch, attacking trees of all ages. If the trees 

 are not killed they produce but a poor grade of timber and 

 poor growth, and are moreover rendered liable to the at- 

 tacks of wood-rotting fungi. All larches infected with 

 mistletoe should be cut, whether salable or not. 



