June 2, 1920.] 



Agricultural Gazette of N.S.W, 



439 



Collar Rot of Citrus Trees* 



C. 0. HAMBLIN, B.Sc, B.Sc. Agr., Assistant Biologist. 



Collar rot is found in many, if not all, of tlie citrus-growing countries of 

 the world. It recurs fairly frequently in Australia, but, unfortunately, often 

 escapes the notice of growers until serious damage has been done. It is with 

 a view to calling the attention of grov^ers to a prevalent disease that these 

 notes are compiled. 



Base of diseased tree showing " gumming ' 

 the trunk (on the left). 



Spores of the fungus {Fusarium limoiiis Briosi), 

 after McAlpine. 



Collar rot manifests itself most frequently by " gumming " on the trunk 

 just above, or close to, the ground. In many cases if the ar^a of gumming 

 is examined the bark in the vicinity will be found dry and brittle. Trees 

 may be attacked at all ages. When the young tree is attacked there may be 

 chlorosis or " yellowing " of the leaves, especially on terminal twigs, but with 

 older trees this yellowing may not appear until the tree has been nearly 

 vingbarked at the trunk. 



Constantly in association with the disease is a fungus parasite (Fusarium 

 limonis), which first makes its inroads through an injury or through water- 



