9 



sufficiently to appear as an olive brown spot or scab. This 

 early establishment of the fungus is known as the primary 

 infection. It is usually the underside of the unfolding 

 leaves and the pedicles of the blossoms that are first infect- 

 ed. The spots developing on the pedicles cause the young 

 fruits to drop within a week or two after blossoming while 

 on the infected leaves, spots develop from which great num- 

 bers of summer spores or conidia are developed, which fall- 

 ing on the surface of the leaves below and on the upturned 

 blossom ends of the rapidly enlarging friuts give rise to the 

 black scab spots on the upper side of the leaves and fruits. 

 Prom these spots new crops of conidia are produced which 

 spread the parasite to other leaves and fruits throughout the 

 season, whenever rainy weather favor. The ascospores de- 

 scribed as causing the first or primary infection may contin- 

 ue to be discharged over a period of a month, so that if 

 weather is not propitious for discharge just before blossom- 

 mg time primary infection may occur later, after the blos- 

 soms have fallen. It is, however, generally the primary in- 

 fection before blossoms that destroys the set of the fruit and 

 the secondary infections later that gives scabby fruit. Not 

 infrequently one of these secondary' infections occurs later in 

 the summer, August or September, making scabby a crop 

 which up to this time had been clean. This is known as the 

 late infection. This late infection sometimes does not de- 

 velop until after the apples have gone into storage. Late 

 infection scab spots are not confined to the blossom end of 

 the fruits like the earlier lesions but are apt to be more 

 common about the stem end of the fruit. They are, more- 

 over, much smaller, seldom larger than a pin head arid in- 

 tensely black. The scabbing of the current year's twig 

 growth is known to occur in a few varieties but is not com- 

 mon. There is little evidence to indicate that the apple 

 scab fungus like the pear scab fungus winters on the twigs 

 or limbs of the tree. Neith-er do the fallen scabbed fruits 

 serve to carry the fungus through the winter. The eonidia 

 or summer spores are short lived and refuse to germinate 



