CERTAIN ELEMENTS IN NURSERY PRACTICE 205 



red to dark brown, and a minute slightly elevated black area 

 appears in the center of the spot. 



The spots are circular in outline and may be so numerous 

 as to involve most of the leaf tissue. When the trees are 

 severely attacked the leaves turn yellow or brown, especially 

 those of quince, and readily fall. The disease also affects the 

 twigs to some extent. Leaf-blight may be distinguished from 

 the septoria leaf-spot as the spots are smaller, more colored 

 when young, and somewhat more circular. The septoria spots 

 are apparent on the under surface of the 

 leaf. In the nursery, septoria spot is gen- 

 erally found on budded pears, while leaf- 

 blight is commoner on quinces and pear 

 seedlings (Fig. 218). 



Cause. - - The leaf-blight disease is 

 caused by Fabrcea maculata. The small 

 black specks previously mentioned, which 

 develop in the center of the affected areas 

 of the leaf, are the reproductive bodies 

 (acervuli) of the fungus. Within the FlG - 218 - Leaf-blight 



1 ' J 1 J 1 U f <l uince - 



acervulus spores are developed, which 

 on being discharged are carried by wind and rain to the 

 foliage. Under favorable conditions, with the presence of 

 moisture, the spores germinate and produce new infections. In 

 this way the fungus is propagated throughout the summer. 

 Some of the spores may live over winter on the diseased twigs 

 and produce new infections when growth starts in spring; 

 but no doubt the greater proportion of infections in early 

 spring is due to the sexual stage (perithecia) of the parasite. 

 The perithecia develop on the fallen leaves, and the next 

 spring discharge many spores which produce the first infec- 

 tions of the season. 



Control. Spraying with lime-sulfur solution 1 to 40, or 

 dusting with a mixture of 95 parts finely ground sulfur and 



