CALIFORNIA AVOCADO ASSOCIATION 



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rafRa. On one tree a cut of the same kind without inoculation was 

 made and covered as the others to serve as a check. 



When the inoculated trunks were first examined on October 22, 1914, 

 a watery, slightly colored liquid was running from both cuts, and below one 

 of them the white crystalline substance seen on the original specimen, was 

 being deposited as the exuding liquid dried. The check cut was already 

 beginning to heal without any deposit. 



On January 14, 1915, a considerable deposit of the white crystalline sub- 

 stance had formed at both of the inoculated cuts and the larger area of 

 killed bark was three-fourths of an inch wide and two and one-half inches 

 long. The wood was affected only to a slight depth. The affected bark 

 and wood were cut out at this time to save the trees and four culture 

 tests made as described before from the advancing edge of one of the dis- 

 eased areas. Three of these cultures developed Pythiacystis as before. 

 The incision on the check tree healed rapidly without apparent injury to 

 the adjoining bark. 



One of the original cultures was kept alive by transfers every one to 

 five months, and on March 28, 1916, further inoculations were made into 

 avocado trunks with it and also with the fungus Pythiacystis citrophthora 

 isolated from diseased bark of lemon Gummosis. Two inoculations from 

 each culture were made and two additional cuts were made to serve as 

 checks. All were wrapped in the same manner as in the previous inocula- 

 tion. All inoculated cuts were showing the white crystalline deposit by 

 April 7, 1916, and the bark about the cuts was discolored. On May 15, a 

 large deposit of this white substance had formed below all the inoculated 

 cuts. The effect on avocado of the lemon Pythiacystis was about the same 

 as the avocado Pythiacystis. A diseased area of each kind was cut out. 

 These showed the cambium killed over an area of three-fourths of an inch, 

 wide and two and one-half inches long. The avocado Pythiacystis was 

 again recovered from the advancing edge of a diseased area. The cuts 

 serving for checks healed rapidly without apparent injury to the tree. 



The same two cultures were tested out on young orange trees at the 

 same time. The lemon Pythiacystis produced Gummosis on the orange 

 with killing of bark adjacent to the cut. The avocado Pythiacystis, how- 

 ever, produced no effect, the cuts healing almost as rapidly as the checks. 



Preventive Measures Suggested. — Since the fungus itself and the 

 effects of the disease are similar to that of Pythiacystis on citrus trees, 

 the same methods for prevention and treatment, if carefully carried out, 

 will probably apply to a large extent at least to the avocado. Good 

 drainage, an avoidance of too much water at the base of the tree, keep- 

 ing the soil from washing in and piling up against the trunks and avoid- 

 ing planting too deep, especially on heavy soils, will undoubtedly serve 

 to prevent the disease. If it occurs on large trees and is found before 

 it has gone too far, the dead bark can be carefully dissected out and 

 the wound thus made disinfected. After the cut edges begin to heal 

 the exposed wood can then be covered with wax or other good covering. 

 If the bark is killed all the way 'round when discovered, the tree will, 

 of course, eventually die. Mr. Ryerson writes, "The spots were not com- 

 mon and in reality did not cause serious damage unless found on par- 



