120 MANUAL OF TREE DISEASES 



ascospores are formed in the dead leaves after they fall to the 

 ground. These spores mature at about the time the new leaves 

 appear in the spring and are disseminated by the wind and 

 spattering drops of rain. The lower leaves of young trees and 

 sometimes of older ones are the first to show infections in the 

 spring, because they are closer to the source of spore-production. 

 The first lesions soon develop the other type of fruiting-bodies 

 on the dead areas mentioned above. These appear as minute 

 black dots. In this stage the fungus is known as PhyUosticta 

 sphesropsoidea. The spores are extruded from the fruiting- 

 body and are mainly distributed to healthy foliage by wind and 

 rain. By repeated generations of this kind of spores, all the 

 leaves on a tree may become infected in a short time. Con- 

 tinued or periodically rainy seasons are especially favorable for 

 an epiphytotic, since moisture conditions necessary for germina- 

 tion are furnished for each new crop of spores. At such times 

 the foliage from a distance appears as if scorched by fire and 

 considerable defoliation may result. 



Control of leaf-blotch. 



In the niffsery it has proved beneficial, in preventing to some 

 ejctent the amount of primary infection, to plow under or rake 

 together and burn all dead leaves around the trees. This 

 practice can be applied to shade-trees and thus eliminate to a 

 large degree the source of early infections. Even when such 

 measures are taken, a slight amount of infection may result 

 from bits of leaves left on the ground or from early infections on 

 trees in the vicinity. It is, therefore, necessary to supplement 

 these measures by coating the leaves with some efficient 

 fungicide at the time weather conditions ajid the development 

 of the leaves are conducive to infection. Spraying with lime-sul- 

 fur (1-50) or bordeaux mixture (5-5-50) will prevent infection. 

 The foliage is so dense, however, that thorough spraying cannot 

 be done without drenching the foliage. This may lead to 



