74 DISEASES OF ECONOMIC PLANTS 



mated the damage to the apple crop of the United States 

 that year as $10,000,000. There is often a loss of from 

 50 to 75 per cent of the crop. 



Two modes of treatment used in conjunction are useful : 

 first, to cut off and burn the cankers and to hand pick and 

 destroy munmiified fruit ; second, to spray the growing fruit 

 with a fungicide. The mummified fruit should all be col- 

 lected and all cankers, so far as they can be detected by the 

 most searching inspection, should be taken out. The trees 

 should be sprayed once before the buds open, and frequently 

 thereafter until the fruits are almost ripe, with Bordeaux 

 mixture, or self-boiled lime-sulphur wash. A non-spotting 

 spray should be used for the last application. 



Scab {Venturia inaequalis (Cke.) Wint.). — This is justly 

 called the most injurious disease with which the apple 

 grower has to contend. It affects both fruit and leaves, 

 probably in all localities where apples are grown, and is seri- 

 ous in Europe, Australia, and New Zealand, as well as in 

 America. 



Upon the fruit, the scab first causes the skin to take on a 

 dark olive-green color; later as the outer skin breaks and 

 exposes the fungus underneath the color changes to black. 

 An apple in this stage is shown in Fig. 25. Still later the 

 scab enlarges, and the spores and fungous cells at the center 

 of the spot may fall away, leaving a skin of rusty appear- 

 ance surrounded by a dark ring where the fungus has not 

 yet fallen off. Still further out may be an olive-green or 

 silvery ring, showing the still younger stage of the disease. 

 Cracking and distortion occur in cases of very badly 

 affected fruits. Scabby fruits are much more susceptible 

 to bin rot than are clean fruits, p. 94. 



