36 MISC. PUBLICATION 4 9 8, U. S. DEPT. OF AGRICULTURE 



CONTROL MEASURES 



Control of the decay is effected chiefly by preventing skin breaks in 

 the fruit. The fruit should be clipped instead of pulled from the tree 

 and should be handled carefully during all marketing operations. In 

 Florida three applications of bordeaux mixture to the tree as recom- 

 mended for the control of blotch will also effectively control 

 anthracnose. It is probable that the effect of these sprays on anthrac- 

 nose is chiefly due to preventing openings in the skin caused by the 

 blotch fungus. 



(See 63, 67, 82, 97, 113, 115, 116, 145.) 



BLOTCH (CERCOSPORA SPOT) 

 {Cercospora sp., probably C. purpurea Cke.) 



Blotch, or cercospora spot, has been reported chiefly from Florida, 

 but, because it appears only as a surface blemish and frequently in con- 

 nection with anthracnose, it may have been overlooked in the West 

 Indies and South America. In Florida it is widely distributed over the 

 avocado-producing districts and constitutes one of the important dis- 

 eases of this fruit. 



The disease appears on the foliage, fruit, and young stems. On the 

 leaves the lesions are angular and brown to dark brown. They are 

 usually scattered but may coalesce to form large brown areas. In 

 severe cases the leaves drop prematurely. 



Blotch is apparently capable of attacking the fruit at any stage of its 

 development on the tree. At first the spots appear as greenish-white 

 dots that slowly develop into small, irregular, slightly sunken, hard, 

 surface blotches. Their color is brown or dark brown except in the 

 center of the spot, where frequently a small white tuft of the causal 

 fungus is visible. The surface of the spot is usually cracked and 

 fissured. 



On the fruit, blotch is a surface blemish only, never penetrating the 

 flesh. Because the spots crack and expose the flesh beneath they open 

 the way for decay by secondary organisms, particularly by Colleto- 

 trichum, which commonly accompanies blotch on mature fruit. It has 

 been found that if blotch is controlled, little trouble is experienced from 

 anthracnose. 



The species of Cercospora that causes blotch apparently lives over 

 from one season to the next on infected leaves. 



Blotch can be controlled by proper application of bordeaux mixture. 

 It is necessary to apply the fungicide at least three times at monthly 

 intervals beginning in early May. For varieties maturing in late 

 winter and early spring an additional application in early September 

 should be made. 



(See 113, 116, 145.) 



DOTHIORELLA ROT 



(Dothiorella gregaria Sacc. 9 ) 



Dothiorella rot of avocados is important only on fruit from certain 

 coastal districts in California. The decay usually does not affect fruits 



Perfect stage, Botyrosphaeria ribis Shear, Stevens, and Wilcox. 



