CROWN GALL 



281 



peach yellows. There is nothing that can be done with 

 infected trees except to uproot and burn them. 



Crown Gall. Crown gall causes unsightly swellings to 

 appear on the roots of fruit trees. It is most frequently 

 found on young 

 nursery stock. 

 From the enlarged 

 swellings or knots, 

 numerous fine roots 

 are frequently pro- 

 duced, hence this 

 disease is often 



called "hairy root/ 7 Fig ^- Roots infected with crown 

 The extent of the injury caused by it is not definitely 

 known, but it is probable that the vitality of the tree is 

 seriously weakened. Nursery stock should be examined 

 before planting, and infected stock should be rejected. 

 This is the only preventive practiced by the fruit grower. 



EXERCISES 



1. Give examples of chewing insects, sucking insects, bac- 

 terial diseases, and fungous diseases. 



2. Why is an orchard planted in a hollow more susceptible 

 to fungous diseases than one upon high sloping land ? 



3. How does the method of pruning exercise an influence 

 over disease control ? 



4. Examine bare twigs and storage apples for San Jose scale. 

 With a pin lift the scale from the insect and examine each with 

 the lens. What spray is used against this pest and when is it 

 applied ? 



5. Obtain three perfectly sound apples. Break the skin of 

 one, bruise another without breaking the skin, and leave the 



