26 Diseases of Greenhouse Crops 



Heterodera radicicola there is another nematode 

 which confines its injury to foliage only. 



Of the greenhouse hosts affected by this pest may 

 be mentioned the Begonia, Asplenium nidus-avis, 

 Pteris serrulata avistata, Pteris wimeseth, Pteris 

 tremula, and Pelargonium. 



Sym-ptoms. On the Cincinnati begonia the symp- 

 toms, according to Clinton,* are manifested as nu- 

 merous small indistinct discolorations limited by the 

 small veinlets. In time, however, the tiny spots en- 

 large and unite, forming a conspicuous reddish-brown 

 blotch. Frequently infection is manifested as long 

 streaks along the main veins. Often isolated spots 

 occur in the midst of the surroimding healthy tissue 

 (fig. 5, a.). On Asplenium nidus-avis, the trouble 

 becomes conspicuous in dark brown areas from the 

 base of the leaf near the midrib. These spread ujv 

 ward until the entire lower half of the leaf is killed. 

 On Pteris, the spots appear as reddish brown bands 

 reaching out from the midrib to the border, but lim- 

 ited sidewise by the small parallel cross veins (fig. 



5, b.). 



The Organism. The nematode in question is a 

 slender microscopical worm. The latter chooses the 

 air chamber of the leaf in which to lay its eggs and 

 upon hatching travels around in different parts of 

 the same leaf or to the neighboring foliage. The 

 worm can travel only when there is a wet film on 

 the leaves. 



•Clinton, G. P., Connecticut Agr. Expt Sta, Thirty-ninth Ann. 

 Rept.: 455-462, 1916. 



