CITEUS DISEASES. 83 



MISTLETOE (Dendropemon spp.). 



Parasites belonging to this group occur in a number of localities, 

 particularly in the western part of the citrus district. The plants 

 may be present as isolated specimens only, or at times may be so 

 abundant as to cause considerable injury to the host tree. Mistletoe 

 is a true flowering plant in contrast to the other parasites of citrus, 

 which are fungi. It reproduces by means of seed enclosed in a 

 sticky pulp, which causes them to adhere firmly to a branch or other 

 object with which they come in contact. Birds are very efficient 

 carriers, and are largely responsible for the spread of the parasite. 



The seeds germinate and send root-like processes into the tissues 

 of the host, erect shrubby plants developing. Possessed of green 

 leaves, the mistletoe to a considerable extent manufactures its own 

 food supply, but draws entirely, of course upon the host for raw 

 materials, water and dissolved mineral salts. The limbs attacked die 

 beyond the point of entrance of the parasite, the water supply being 

 diverted to the latter. This results in an unsightly appearance, as 

 well as a reduction in the bearing surface of the tree. 



At least two species are found on citrus (orange and grapefruit) 

 Dendropemon hicolor and D. caribaeum, both of which also occur 

 on a considerable range of other hosts, some of economic importance. 



As a control measure, the pruning out of infested limbs is feas- 

 ible, together with similar action in neighboring non-citrus host trees, 

 or even the removal of the latter if they are of no particular value, 

 or heavily infested. 



SCAB.^ 



Of the various diseases of grapefruit in Porto Rico, citrus scab, 

 or lemon scab, has beyond much doubt assumed a position of first 

 rank, and has been one of the chief agents in sending fruit to the 

 cull pile and in the lowering of grades. During the past four or 

 possibly five seasons — the time in which the disease has been espe- 

 cially virulent — it has l)een not at all uncommon in certain districts 

 for the larger part of the crop of a number of groves to be so dis- 

 figured as to be worthless, representing a total loss on the season's 

 work. 



This has been especially true in those seasons when low prices 

 have made it impracticable to ship anything but the highest quality 

 of fruit. It would be extremely difficult to give any estimate of 

 the losses that have been sustained, but they will reach a total of 



' Abridged from Bulletin 17, Insular Experiment Station. 



