40 Pomona College Journal of Economic Botany 



spot is probably caused by the weakening of the tree due to the gummosis 

 rather than any other reason. It might naturally be expected to find the 

 wither-tip upon any diseased trees which are suffering from Gummosis, Die- 

 back, Foot-rot, etc. 



Lack of Care. — Poorly fed trees have been observed to succumb to this 

 disease first — the leaves showing the spots, the twigs dying, and the fruit 

 spotted before it appeared elsewhere. The cure is obvious. 



Moisture. — This is perhaps the most important factor in contributing to 

 the growth of this disease. As with all of the fungi a moist condition 

 produces ready and rapid germination and excellent conditions for future 

 growth. The early observations of the wither-tip were all connected with 

 the belief that it could thrive only in a very moist climate. This belief 

 caused some surprise to the Florida experts who thought that the climate 

 in California was too dry. 



The attack in Ventura County was preceded by an unusually heavy rain 

 which brought on the attack almost immediately. 



It will probably be found in any citrus growing community which receives 

 any rainfall at all, from the fact that it has been observed in Arizona, but 

 only during the winter months. 



In a wet country much trouble must be expected from this disease. 



A systematic application of sprays should be continued throughout the 

 year, in plots at least, so as to be sure of the advantages of the preventative 

 work of fungicides. 



TREES ATTACKED IN VENTURA COUNTY 



SEVERE attacks: 



Variety Location 

 Havana Sweet Seedling Orange Santa Paula. 



Navel Orange " 



Valencia Oranges " and Saticoy. 



Eureka Lemons " 



Lisbon Lemons " 

 Slight Attacks. 



All citrus trees in this county. 



MODES OF DISTRIBUTION 



Wind. — The spores are so minute that when they become dry they may 

 be carried for miles by the wind. These spores are usually blown into the 

 tops of the trees and the heavier attacks may be expected in these places. 

 In Southern California it must be expected that, if the disease is common 

 along the coast, that the coast winds are sure to carry the spores to all 

 inland sections and these need only the moisture conditions to produce the 

 disease. 



Water. — If the spores find lodgment in the tops of the trees they are sure 

 to be carried to all parts of the undergrowth by the first rain. This 

 is the most effectual way of infecting all parts of the tree. The "Tear-stain" 

 is produced by the dripping of the water from an infected twig or "Mummy" 

 to an uninfested lemon. 



