328 Diseases of Greenhouse Crops 



Septoria Leaf Spot 



Caused by Septoria roscz Desm. 



Symptoms. This disease is characterized by dis- 

 tinct spots on the foliage (fig. 66, h.). Spots 

 with centers of creamy or dirty white surrounded 

 by broad purple margins appear on the foliage. The 

 pycnidia are formed in the center of the spots. Lit- 

 tle is known of the nature of the causal organism. 

 The destruction of all infected material by fire and 

 spraying with a standard fungicide will keep the 

 disease in check. 



Stem Canker 



Caused by Coniothyrium fuckelii Sacc. 



Symptoms. This disease usually produces cankers 

 of the canes and branches. The lesions are brown 

 in the center with a black border, limited by an out- 

 ward reddish band or zone. The same disease at- 

 tacks apples and raspberries. 



The Organism. It has long been suspected that 

 Leptosphseria was the ascus stage of Coniothyrium 

 fuckelii. This Stewart seems to have verified, 

 although definite evidences are still lacking. The 

 perithecia are in groups, globose, black with fringed 

 mouths. The asci are cylindric, eight-spored, one- 

 rowed, three-septate. The pycnidia are similar to 

 the perithecia; the spores are ovate, continuous, and 



♦Stewart, F. C, New York (Geneva) Agr. Expt. Sta. Bui. 328: 

 387, 1910. 



