CALIFORNIA AVOCADO ASSOCIATION 



81 



brown spots from the size of a pinhead to that of a dime. "That tree has 

 black spot," said he. I told him of the basin being flooded for several 

 days and he expressed the opinion that the disease was caused by too much 

 water. So when my trees about September 1 of this year began showing 

 those same purplish brown spots, I came to the conclusion that my soil is 

 too tight to irrigate every two weeks. 



The Lyon tree I have spoken of dropped all its leaves after they had 

 turned brown and withered, and new weak looking leaf buds started to 

 break; but after lingering until this spring it died. The leaves of the trees 

 affected this year, have also dropped off, in some instances leaving the 

 trees entirely bare. Some of the trees have already withered and died, 

 while others have developed new young leaves. On some of the trees these 

 new leaves are fresh and healthy looking, while on others the young leaves, 

 sometimes before they are an inch long, begin to show the black spot around 

 the edges and the leaves curl and wither and in a short time drop off. In 

 extreme cases the tips of the limbs also wither and die. 



I have not found the disease restricted to any particular variety of 

 tree. It has appeared on some of each of the following: Northrop, Val de 

 Flor, Harman, Queretaro, San Sebastian, Taft, Fuerte, Grande, Solano, 

 Dickinson, Merito, Ameca, Sharpless, Lyon, Walker, and Meserve. None 

 of the Puebla trees were affected, nor the Spinks, Perfecto, nor Monte- 

 zuma. So I suppose those trees can stand more water than the others as 

 they were all treated exactly alike. The trees introduced by Mr. Knight 

 were generally immune, only two or three out of over fifty being slightly 

 affected. 



As an instance showing how little water an avocado tree can receive 

 and yet live, I will say that last year while planting some trees, the bud 

 was broken off one tree. The ball was thrown aside and lay on top of the 

 ground exposed to the sun for six or seven weeks until it was as hard and 

 dry as a bone. Through curiosity to see if it would grow, I planted the 

 stump near a house occupied by a Japanese. The waste water from the 

 house flowed by a few feet away. That was all the irrigation it ever got. 

 It has never been cultivated and never fertilized. It is now nearly 1 feet 

 high and looks better than any of the trees upon which I have devoted so 

 much work and care. 



From my experience I am convinced that the amount of irrigation re- 

 quired depends entirely upon the nature of the soil. Next year I shall irri- 

 gate perhaps as frequently as this year but I shall not use the basin system 

 nor shall I use so much water. 



E. E. Knight: Some varieties seem not to be affected with the mottle 

 or brown leaf. Others are hardly ever free from this condition. I se- 

 lected a tree in the center of my orchard and irrigated it from two to three 

 times each week. It developed the brown spots, but in the center of the 

 leaf, none around the edge. As a rule the brown makes its appearance at 

 the end or on the edge of the leaves. I would offer as a suggestion that 

 too much water affects the center and a lack of water the outside of the 

 leaf. 



Dr. Keller: I think that the spots on the edge of the leaf are from 

 lack of water. 



Mrs. J. T. Stewart: I have an avocado orchard of 15 acres which is 



