CITRUS CULTURE IN HAWAII 



17 



set on mounds the soil of which gradually wears away in a few 

 years, leaving the crown roots exposed to the air. These roots 

 are naturally more resistant than is the trunk to the soil fungi 

 producing gummosis. As a further precaution the exposed parts 

 of the roots and the lower part of the trunk should be treated 

 with Bordeaux paste. Any depression about the base of the 

 tree or the crown roots should be kept drained. Fawcett and 

 Lee (11, p. HO) give several remarkable examples of the success 

 of this treatment in California, and this method of combating 

 gummosis is also reported to be successful in both Egypt and 

 Palestine. When gummosis is discovered, the soil about the base 

 of the trunk should be removed to expose the upper part of the 

 crown roots. All diseased bark should be cut away and the en- 

 tire trunk treated with Bordeaux paste (1 pound of bluestone 

 and 2 pounds of unslaked lime with enough water to make a thick 

 whitewash). On heavily fungus-infested soils this paste should 

 be applied to the trunks of all the citrus trees, including the 

 healthy ones, to safeguard them from gummosis. The treat- 

 ment should be repeated every two years. 



Psorosis or Scaly Bark 



Psorosis is peculiar to the orange tree and is of limited occur- 

 rence in most citrus-growing countries. In some places it is 

 confused with the general name of gummosis and is known as 

 scaly bark or scaly bark gum disease. At the station the orange 

 tree has been less severely attacked by this disease than by 

 gummosis. The most conspicuous evidence of psorosis is the 

 scaly character of the outer bark on the larger branches or the 

 trunk of the affected tree. The scales are less than an inch 

 across and curl up and drop, leaving the inner bark exposed. 

 At certain seasons, or at certain stages of the disease, gum ex- 

 udations may occur. Psorosis develops very slowly, and several 

 years may pass before the foliage shows its effects. The leaves 

 shrink, turn yellow, and are few in number, the twigs die back, 

 and new shoots attempt to grow near the trunk. Five years 

 or more may pass before the disease kills an orange tree. Smith 

 and Smith (25, p. 1135) are of the opinion that scaly bark "ap- 

 parently originates in an irregular moisture condition of the 

 soil." They show that the disease has occurred in California 

 "when irrigation by flooding was generally practiced and cultiva- 

 tion received little attention." 



Treatment — Where only the branches are affected the tree 

 may recover if the dead parts are cut off and the wounds are 

 coated with thin Bordeaux paste. Where the trunk is only mod- 

 erately affected the diseased portion should be cut out and the 

 wounds treated with Bordeaux paste. Seriously affected trees 

 cannot be saved and should be replaced. The disease is not con- 

 tagious. 



Verrucosis or Lemon Scab 



Verrucosis or lemon scab (Sporotrichum citri; Sphaceloma 

 fawcettii) occasionally attacks lemon fruits growing in moist 

 localities in the Hawaiian Islands. Fawcett and Lee (11, p. 485- 



