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DEPARTMEXT OF AaRIClJLTURE;^^'^OHN ' 



Vol. III. FEBRUARY. 1905. Part 2. 



WITHER-TIP AND OTHER DISEASES OF CITRUS 

 TREES AND FRUITS CAUSED BY COLLETO- 

 TRICHUM GLCEOSPORIOIDES.* 



By P. H. Rolfs, Pathologist in charge of Sub-tropical Laboratory. 



INTRODUCTION. 

 The group of diseases discussed in this bulletin was unknown 

 in Florida until a comparatively recent time. " * At first recorded 

 as of merely passing interest, the attacks of the fungus Colletotrichum 

 glooosporioides have since increased in severity until they are now 

 assuming serious proportions in various citrus crops. The amount 

 of damage done by lemon-spot is often sufficient to eliminate the 

 profits of the shipments in which the disease occurs. As wither- 

 tip it repeatedly kills back the new growth of young trees until 

 their vitality is exhausted. On large trees the small twigs are 

 cut off, thus preventing the tree from producing the bloom neces- 

 sary to set a heavy crop. As anthracnose and canker of lime it 

 has caused an almost total destruction of the crop where the 

 disease has gained a foothold. 



The fact that the attack of this fungus manifests itself in vari- 

 ous diseases has greatly complicated the work and added im- 

 mensely to the labour of demonstrating its identity. The results 

 of the microscopic work indicated that these various diseases — 

 wither-tip, leaf-spot, lemon-spot, canker, and anthracnose — were 

 produced by one species of fungus. It remained for cross inocu- 

 lation with pure cultures to confirm this supposition. In most 

 cases these cross inoculations took readily, while in others it was 

 difficult to induce the fungus to make an attack. This was 

 especially the case in attempting to produce lemon-spot. Infection 

 at the stigma of lime blossoms is one of the inoculations most 

 easily accomplished. 



Leaf-spot is easily produced artificially on foliage infested with 

 purple mites. To produce such an infection a leaf must be washed 

 carefully to free it from danger of natural infection, and then 



* Bn. r,2, B. of PI. Ind. U. S. Dept. of Agri. 



** I have lately lonnd this disease in Jamaica on limes. Editor, BuVyetin of the 

 Department of Agriculture. 



