416 Diseases of Economic Plants 



and disintegrated, resulting in the death of the more distal 

 portions of the plant. 



A striking feature is the tendency of this disease to infect 

 to a large degree one variety, the Mrs. Thomas W. Lawson, 

 to the exemption of others. 



Stem-rot, wilt ^^- (Fusarium sp.). — Described in 1897 by 

 Sturgis, this rot occurs chiefly upon the stems and larger 

 branches, discoloring the wood and killing the bark, but 

 rarely causing soft rot. The diseased plant dies gradually 

 with yellowing and drying of the foliage, much as though 

 due to insufficient water supply. 



When practicable, beds should be disinfected and new 

 uninfected stock introduced. The disease when first intro- 

 duced upon a few plants can be stopped by the immediate 

 removal and destruction by fire of the diseased plants. 



Leaf-mold (Heterosporium echinulatum (Berk.) Cke.). — 

 Circular spots, 1-4 mm. in diameter, bearing more or less 

 concentric zones of dark mold, appear upon the leaves, espe- 

 cially the younger ones, also upon the stems and sometimes 

 upon the calyx. Mold upon the calyx results in deformed 

 flower parts. In some instances the whole top of a plant 

 becomes moldy. 



Infested refuse and leaves should be burned and Bordeaux 

 mixture employed as a spray. 



Bacterial-spot ^^^' ^'"* (Pseudomonas woodsii (EFS)). — 

 The spots of the leaves and stems are small, usually sur- 

 rounded by a narrow water-soaked area, while the center is 

 commonly slightly brown. As the spots grow larger they 

 resemble Septoria spots with the exception of the water- 

 soaked margin. Later they dry and collapse. Badly diseased 

 leaves wither. In some cases nearly all the leaves on many 

 of the stems are so badly diseased as to be hopeless. 



This trouble can be checked by removing and burning 

 all diseased leaves, then spraying with formalin, 1 part to 500. 

 A somewhat similar spot caused by Aphides is known as 

 Stigmonose. 



Gray-mold {Botrytis sp.). — A gray-mold similar to that 



