CITRUS DISEASES. 65 



As a further step in tlie same direction, close planting should be 

 avoided, or in old groves, which have closed in, some pruning or 

 even the removal of part of the trees to admit light and permit 

 better air circulation around the trunks will be desirable. When the 

 disease is present, or its presence due to natural conditions is feared, 

 care should also be taken to keep the dirt away from the crown of 

 the tree. A rank growth of vegetation should not be permitted under 

 the trees. A very important*point will be to prevent injury to the 

 trunk or roots from hoes, or other cultivation implements. 



fn Florida excessive applications of organic fertilizers are some- 

 times supposed to aid the disease, but it is not thought that this 

 po sibility need he feared under Porto Rican conditions. 



GUM DISEASES, GUMMOSIS. 



Several distinct diseases attack the trunk and limbs of citrus trees, 

 with symptoms so similar that much confusion has resulted in at- 

 tempts at classifying them. Fawcett '^ in a very clear presentation 

 of the subject recognizes seven types of gum disease, of which at 

 least three are known to be present in Porto Rico. The others, root 

 rot due to Armillaria mellea, a mushroom ; Florida scaly bark, or 

 nail head rust; lu-own i-ot, or Pythiacystis gummosis; and Botrytis 

 or gray fungus gummosis do not, to the best of the writer's knowl- 

 edge. oc(;ur here. Of the other three mal-di-gomma has already been 

 dealt with, and an account will follow of the remaining tw^o, psorosis 

 or California scaly bark, and Diplodia guuuiiing. 



PSOROSIS OR SCALY BARK. 



This disease, wliich is of consideral)l(> importance in Florida and 

 California, is fortunately one which causes little concern in Porto 

 Rico. In its characteristic form it is primarily a disease of the orange, 

 and has been found in a few groves only. In as much as orange 

 growing, as far as the cultivated groves are concerned, is decreasing 

 little fear need be entertained of this disease ever becoming serious. 

 It must not be confused with the nailhead rust, or scaly l)ark disease 

 of Florida, which while very similar in outward respects, is due to a 

 specific fungus, and attacks the fruit in addition. For this reason 



' Cal. Agric. Exp. Sta. Bui. 262. See Bibliography; 



