282 CITRUS FRUITS AND THEIR CULTURE. 



used to protect the trees, the presence of dry herbage 

 among them is a menace to the safety of the grove. Fire 

 may easily spread through the grove and the trees suffer 

 greatly in consequence. Moreover, it has been observed 

 in Florida, that trees standing among dead grass and 

 weeds are much more injuriously affected by frost than 

 are those in clean-cultivated soil. Hence, the best prac- 

 tice is to cultivate sufficiently to partially incorporate the 

 dead herbage with the soil about the middle of November. 



The Die-Back Problem. In groves where trees are 

 affected by die-back, the trouble may be seriously aggra- 

 vated by continuance of cultivation. Particularly is this 

 the case where the disease has been caused by the use of 

 organic fertilizers or by too much humus having been in- 

 corporated with the soil. Where the disease is caused by 

 the presence of hard-pan or by poor drainage, and not 

 by cultural mistakes, the problem is, of course, an entirely 

 different one. 



In the former case, however, much may be accom- 

 plished by changing the method of cultivation and ferti- 

 lizing. Cultivation should be discontinued, thereby re 

 stricting the growth of the trees and lessening the amount 

 of available nitrogen in the soil. The fertilizers used 

 should contain no nitrogen and when fertilizers are again 

 applied, organic sources of nitrogen should be rigidly 

 avoided. If beggarweed is growing in the grove, it should 

 be cut frequently and removed. By this line of treatment 

 groves can usually be brought back to their normal con- 

 dition. The question is discussed further in the chapter 

 on Fungous and Physiological Diseases. 



Implements. The implements used for cultivating 

 must be adapted to the soil conditions and in the end 

 each grower should know what will best answer his pur- 



