New York Agricultural Experiment Station. 317 



INTKODUCTION. 



The apple stands first in importance among the cultivated fruits 

 of New York. Within the borders of this State no other fruit is 

 so largely grown for home use and none equals it in commercial 

 importance. It is more or less subject to injury both in foliage 

 and fruit by a disease commonly known as the scab*, which is 

 caused by a parasitic fungus, Fusicladium dendritictim (Wallr.) 

 Fckl. Some kinds of apples are usually quite subject to injury 

 from the scab while others generally suffer but slightly from its 

 attacks. Among the varieties which are naturally susceptible to 

 the disease are Fameuse or Snow, Fall Pippin, Primate and White 

 Winter Pearmain. Among those which are resistant to the dis- 

 ease in a marked degree are Ben Davis, Black Gilliflower, Grimes 

 Golden, Hubbardston, Maiden Blush, Talman and Yellow Trans- 

 parent. It is certain that local conditions influence the spread of 

 the disease because the same variety is injured more by it in some 

 localities than in others. Moist locations offer conditions which 

 favor its development. 



It is well known that the amount of injury from the scab varies 

 with the season. Continued dark, wet, cool weather at blooming 

 time and immediately thereafter favors the growth and spread of 

 the fungus and may bring about such an outbreak of the scab as 

 to cause the destruction of large numbers of forming fruits, thus 

 greatly diminishing the crop. Under such conditions of light, 

 moisture and temperature the young foliage and fruit are abnor- 

 mally developed and become unusually susceptible to the attacks 

 of the fungus, while these very conditions favor, or at least are 

 not unfavorable, to the healthy growth of the fungus. 



From what has been said in the preceding paragraphs it appears 



that the amount of injury which is caused by the scab fungus 



■ I 



*This disease, as it occurs on the fruit, is so well known that it is unnecessary to- 

 give an extended description of it here. In very severe attacks It forms great brown 

 patches which crack open, disfigure the fruit and render it unfit for market. The 

 injured spots vary in size from such as these down to minute dots which easily pass 

 unnoticed. On the leaves the fungus forms olive-brown patches varying in size as oa 

 the fruit. The spots occur on either the upper or under surface and often cause the 

 leaf to become crumpled. The diseased tissue may finally crack and fall away, thus 

 giving the leaves a ragged appearance. 



