330 



Diseases of Economic Plants 



These are true rusts, and on the white clover possess all 

 of the three stages, cluster-cup, summer or ureclinial, and 

 winter or teliospores. They attack all green parts of the 

 plant. The most conspicuous and destructive stage is the 

 uredinial, which is marked loy profuse, circular or elongated, 

 chestnut-brown, powdery sori. These may be few and 

 scattered, ])ut more often they are abundant, nearly covering 

 the leaf, which turns black, dies, and shrivels. The rust is 

 conveyed from plant to plant throughout the summer by 

 spores of this stage. 



The teliospores or urediniospores may appear in the same 

 or separate sori and in either event the teliospores appear 

 later in the season. They are rec- 

 ognized by their darker brown 

 color. The cluster-cup stage, which 

 is less abundant and less injurious 

 than the other stages, may often 

 pass unnoticed. It appears first as 

 pale, swollen regions upon the leaf 

 or petiole. These regions soon 

 show the characteristic cups with 



I orange-colored spores. The cluster- 



cup stage, though not known on 

 red clover, predominates in the 

 early spring upon many other 

 varieties; but the uredinial stage 

 soon gains the ascendancy over it. 

 All three forms may be produced 

 side by side, to some extent, 

 throughout the summer. Hiber- 

 nation probably occurs in two 

 ways, by the teliospores and by the 

 mycelium, which may remain alive 

 in the affected parts over winter. 

 Anthracnose '^'^^^ {Colletotrichum triJoUi Bain). — This an- 

 thracnose is now known on clovers and alfalfa in Tennessee, 

 Ohio, West Virginia, Arkansas, Kentucky, and Delaware. 



Fig. 173. — Antliracnose 

 on red clover stem and 

 petiole. After Jackson. 



