68 JOURNAL OF AGRICULTURE OF P. R. 



the trunk and large limbs, and because the bark is more quickly 

 killed down to the wood, so that open wounds or cankers, through 

 which wood rot infection can occur, are formed early in the progress 

 of the disease. The scaling of the bark so typical of the first form 

 is much less marked in this, often almost completely absent. Nor 

 does the disease enter into any long chronic state as does the other, 

 but is more apt to be thrown off by the tree, or to complete its covirse 

 within a comparatively short time by girdling. • 



As with psorosis the cause is unknown, although observations 

 point to a parasitic origin. Various fungi are commonly encountered 

 in the gumming areas, but neither local studies nor the very extensive 

 tests carried out in Florida have definitely connected any fungus 

 with the disease. 



Control. 



If taken in time verv effective control can be had by the methods 

 outlined under psorosis. The same precautions '' are necessary." 



DIPIX)DIA CANKER AND DIEBACK. 



While little loss, except in one or two groves, has as yet been 

 occasioned by this disease it may easily become most alarming. The 

 writer regards it as the most threatening of all bark diseases. The 

 trunk, branches, and even the twigs are subject to attack. Infection 

 may take place at any point as manifested by gum exudate and 

 browning of the inner bark. Infected bark finally becomes black and 

 dries out. The wood beneath is also attacked, and in the case of the 

 branches penetration in this manner may be complete. The infection 

 may spread over very extensive areas, involving entire limbs and 

 sufficient of the trunk to cause death. There is practically none 

 of the scaling off' of the outer bark noted in psorosis, but merely the 

 death of the bark, with more or less gum flow from cracks and open 

 lesions. 



