92 



ties. A very small percentage of the trees within the 

 state are affected with citrus canker, but when the in- 

 fectious and virulent nature of the disease is realized 

 it is seen that these few trees are a serious menace to 

 the citrus industry in Alabama. It is for this reason 

 that such energetic efforts are being made to prevent 

 its further introduction and spread and to eradicate 

 the disease already present. 



Hosts. 



Citrus canker has been found to occur on many of 

 the species and varieties of citrus. Among them are 

 grape-fruits, King oranges, trifoliate oranges, sweet 

 oranges, naval oranges, mandarines, Satsumas, tanger- 

 ines, lemons and limes. It has been observed in Louisi- 

 ana on species of Fortunella, to which genus the kum- 

 quat oranges belong. Swingle (2) has recorded the pres- 

 ence of canker on kumquats in Japan. It is not equally 

 severe on all of these hosts but grapefruits and tri- 

 foliate oranges seem to be much more susceptible than 

 the other varieties. Satsuma oranges appear to be 

 quite resistant. Trees growing in rows adjacent to 

 badly diseased grapefruits have been observed to re- 

 main free from disease during an entire season. In 

 other cases Satsuma trees in nursery rows have been 

 observed, all of whose leaves were diseased, some of 

 which leaves had several hundred cankerous areas. 



Symptoms of the Diseask, 



Citrus canker manifests itself by the presence of 

 characteristic spots on foliage, twigs, larger branches, 

 and fruits. The diseased areas are usually light brown 

 in color and are raised more or less above the sur- 

 rounding tissue. The cankers are circular in outline 

 when they occur singly and irregular lesions arc form- 

 ed when several spots fuse. The cankerous tissue con- 

 sists of a corky mass of cells covered by the lacerated 

 grayish outer membrane of the liost. The disease was 

 at first mistaken for scab, l)ut it cannot be confused 

 with scab or other leaf troubles when once one has 

 seen citrus canker in its several stages of development. 



Infections on the leaves first appear as small, oily 



(2) U. S. Deparlment of Agriculture, Citrus Canlver in the 

 Philippines. U. S. Department of Agriculture Cir. 1, No. 1, 

 plate 8, 1915. 



