856 THE FKUIT INDUSTRY IN NEW YORK STATE 



but also from codling moth, it is not possible to separate the two 

 very satisfactorily. It has been conservatively estimated that 

 the state of New York alone loses over $3,000,000 annually 

 through failure -to spray for these destructive pests. 



It is rather generally understood by growers as well as by 

 scientists that the apple scab is caused by a fungus. This 

 minute organism spends the winter in the old fallen leaves as 

 partially developed fruiting bodies called perithecia. Under 

 favorable conditions in the spring, these perithecia forcibly dis- 

 chargej their spores (ascospores) into the air. These spores are 

 very light and are carried by slight air currents to the openings 

 buds. This process of ascospore discharge continues for a period 

 of approximately one month, beginning about the time the blos- 

 soms are ready to open, provided (1) that conditions have been 

 right for the maturation of the ascospores, and (2) that there is 

 rain enough to furnish the necessary moisture for the discharge 

 after these spores are ripe. 



The first activities of the ascospores take place on the opening 

 leaves. As they expand from the blossom bud, their lower sur- 

 faces are first to be exposed to the spores from the old leaves on 

 the ground. Hence it may be seen why the lower sides of leaves 

 surrounding the buds are first to show signs of the disease. As 

 long as the leaves are on the tree the growth is very superficial, 

 the fungus living in the outermost portions of them. Within a 

 short time after the spore alights on a leaf, it germinates and 

 penetration is effected. Soon there appears the characteristic 

 brownish olivaceous growth of the parasite, which worms spots 

 with indefinite, fringed margins. Later, summer spores are de- 

 veloped on the leaves and are blown to other leaves, infecting 

 both the upper and lower surfaces. In time the apples have 

 developed, and the summer spores (conidia) may infect them. 

 Not only do the conidia infect young fruit, but the ascospores 

 from the old leaves may continue to infect the apples, even afte-r 

 they are well set. The fruit pedicels may also be infected, re- 

 sulting in a general failure to set fruit. 



The scab spots are most familiar on the fruit, where they are 

 very much the same in size, shape, and color as they are on the 

 upper leaf surface, although perhaps more sharply defined. They 



