82 JOURNAL OF AGEICULTURE OF P. R. 



In some cases branches of considerable size are involved, and more 

 rarel}' even the major portion of a tree. The presence of the disease 

 in this case will be very evident, the dead limbs standing out clearly 

 from the normal portion of the tree. Affected trees show numerous 

 dead twigs, a yellowing and shedding of leaves, and a general un- 

 thrifty appearance. 



It is often difficult, in fact impossible, unless observed in the 

 initial stages, to determine whether the death of the twig is due "to 

 actual attack by the withisrtip fungus, or whether some one of the 

 many other causes which accomplish the same result has been opera- 

 tive, and the fungus merely a follower. A citrus tree tends to pro- 

 duce more wood than can be cared for, so that there is a constant 

 natural pruning going on. Branches whose leaves fail to receive 

 sufficient light to enable them to produce the necessary food supply, 

 die, as well as those which because of their position fail to receive 

 sufficient water. In mose instances the wither-tip fungus, as well as 

 various other fungi, will be found fruiting on wood of this kind. 



Much of the actual disease of this nature that occurs is due to 

 attacks of other fungi, or to the combined attack of one of them and 

 CoUetotrichum. Diplodia, of which more detailed mention -is made 

 elsewhere, is common in such situations. 



Control. 



Preventive measure are primarily recommended, since the pres- 

 ence or absence of the disease is so directly dependent upon . the 

 state of health of the tree, Avhich is in turn influenced by cultural 

 methods under the control of the grower. The most important fac- 

 tors are cultivation and fertilization. Wlien these are given proper 

 attention, the tree will of itself be able to throw off the disease to 

 a large extent. The use of an excess of nitrogen, either as nitrate 

 of soda or in organic form, is to be avoided, since such a practice 

 tends to produce succulent growth with little resistance. A balanced 

 fertilizer (as nearly as the times warrant), whicli will give a nor- 

 mal healthy growth, is recommended. 



Where the disease has actually gained a foothold and some cor- 

 rective measure seems necessary, a thorough pruning out of all dead 

 or weak wood is desirable, combined with sucli corrective steps as 

 are possible. Pruning, if carefully done and reinforced with proper 

 sanitary and cultural steps, will keep the disease in check. Spraying 

 with Bordeaux has often been recommended, but this will seldom 

 if ever be advisable under Porto Rican conditions. 



