144 proceedings: botanical society of WASHINGTON 



campaign for the eradication of the canker disease of citrus fruit and 

 trees. The first observation regarding a plant disease which presuma- 

 bly was citrus canker is with reference to nursery stock introduced 

 into Texas in 1 911. It is not improbable that earlier shipments of 

 nursery stock were infected, and it is certain that many later ship- 

 ments of Citrus trifoliata orange seedlings from Japan, both into Texas 

 and into other Gulf States, were infected. 



Citrus canker is primarily a leaf-spot and fruit-spot, although it also 

 affects twigs and even old bark and wood. In its early stages, how- 

 ever, it resembles the sour-scab of citrus trees, a troublesome but not 

 an especially serious disease that is widely prevalent in the South. 

 Until late in the year 1913 plant pathologists and nurserymen did not 

 clearly distinguish between these two diseases, and, therefore, prior to 

 its recognition and the determination of its serious character, the ship- 

 ment of infected nursery stock was probably taking place throughout 

 the southern areas where citrus culture was being extended. 



During the seasons of 1913 and 19 14 special efforts were made by 

 State nursery inspectors, by nurserymen, and by citrus growers to 

 check the spread of the disease by complete defoliation of infected 

 stock followed by immediate and thorough spraying with strong Bor- 

 deaux mixture and by painting visible infections with Bordeaux paste. 

 These treatments were ineifectual, however, and citrus growers in 

 southeastern Florida became so concerned over the rapid and destruc- 

 tive spread of citrus canker and the failure of the methods usually 

 employed for controlling plant diseases that they originated the plan 

 of spraying infected trees with burning oil, thus completely destroying 

 them. Eradication work of this character was undertaken imme- 

 diately and financed almost entirely by private subscriptions, but the 

 disease appeared to be gaining upon the forces attempting to control it. 



Severe tropical storms, in addition to the usual means of spreading 

 the contagion, considerably increased the number of properties in- 

 fected. The grapefruit, the orange, the lime, and the lemon are so 

 readily infected with citrus canker that it does not appear probable 

 that any method except that of complete destruction of all infected 

 trees will serve to check the disease in any locality. Even at the worst, 

 however, but a very small fraction of the citrus properties of the South 

 have been infected, and those in California have escaped completely. 

 Furthermore, the infected properties usually can be cleansed of the 

 disease before many trees are lost. 



Throughout the last three years great emphasis has been given to 

 the necessity of unusual precautions and constant care to prevent the 

 spread of canker, which is extremely infectious to all kinds of citrus 

 trees. The progress of the work has been very satisfactory, and there 

 appears to be no doubt that the few infections occurring in South 

 Carolina and Georgia have been eradicated, so that further work in 

 these states will not be necessary. The amount of infection in Florida, 

 Alabama, Mississippi, Louisiana, and Texas has been very greatly re- 

 duced, and while very thorough scouting and inspection will be neces- 



