174 DISEASES OF FRUIT TREES 



The knots may develop in new positions or by the side of old 

 knots (Fig. 73). It is very common for them to break out where 

 a small twig joins a branch, the fungus having apparently 

 gained entrance in the angle between the two where the bark is 

 probably less impervious. The disease lives over in the tissues 

 adjoining the old knots and breaks out again either above or 

 below the knot. 



The most practical remedy is to cut out and bium the knots 

 (Figs. 74 and 75). This is especially important in the spring 

 before the spores are produced, but should be kept up through 

 the season. Care should be taken to cut well below the knot, 

 otherv\use the disease may break out again as shown in Figure 74. 

 Spraying, particularly just before the buds break, is also 

 effective. This may be supplemented by an earlier application 

 in late winter and by others during spring and summer if the 

 outbreak is serious. 



QUESTIONS 



1. What is a fungus? 



2. Describe the action of a fungicide. 



3. Describe tlie apple scab. 



4. What methods are recommended for combating the api)le scab? 

 0. vVliat remedies are recommended for rust? 



6. Tell what you can of the disease known as blotch. 



7. Outline the methods of fighting canker. 



8. Describe the work of the fire blight. How may it be controllod? 



9. Describe peach scab. 



10. Describe leaf curl. How is it controlled? 



11. ^\^lat is the most practical method of controlling tlxe black-knot of 



plums and cherries? 



12. What are the worst fruit diseases in your district? 



