Fruit Setting and Pollination 251 



soil management, the fruit-spurs become weak and fail to 

 set fruit-buds which have sufficient vitality to develop into 

 fruit. This often accounts for the crop failure of old trees 

 making little annual growth. In such cases, lack of proper 

 nourishment is more often the cause of unf ruitfulness than 

 lack of cross-pollination. 



2. Insects and diseases prevalent at blooming time may 

 cause a poor set of fruit. Some of the bloom is often 

 destroyed outright by various diseases, particularly apple- 

 scab, anthracnose, or blight. Many blossoms may be 

 ruined in their early development by the attacks of insects. 



3. Extreme vegetative vigor of the tree on account of an 

 excess of certain elements of plant-food may detract from 

 f ruitfulness. Often when a tree is growing too vigorously, 

 it runs largely to wood growth and sets very few blossoms 

 and even these are shed as soon as the blooming period is 

 past. Excessive amounts of nitrate or manure when 

 applied to orchards already making good growth often 

 over-stimulate wood growth to the point at which the trees 

 are almost barren. Furthermore, in such cases the fruit- 

 buds go into the winter in an immature condition with less 

 chance of escaping winter-injury. Most experimenters 

 agree that wood growth can not keep up vigorously during 

 the entire season without sacrificing a healthy set of fruit- 

 buds. 



4. Drought injury to trees may prevent the development 

 of fruit-buds. It has been noted that when excessively 

 long droughts occur, trees produce very little bloom the fol- 

 lowing season. The weakening influence of the drought 

 prevents the formation of fruit-buds with sufficient vitality 

 to form fruit. In such cases the tree requires all its 

 energy to repair vegetative growth, and even though it may 



