64 BULLETIN 12*1, U. S. DEPARTMENT OF .AGRICULTURE. 



has been isolated from soil under diseased plants and from surface 

 drainage water after rains. 



The disease is especially destructive in certain fields where arti- 

 ficial overhead watering is practiced. Convincing evidence of hand 

 dissemination by workmen during the process of culling watermelon 

 fields has been secured. 



The mode of origin of the disease in new fields in original centers 

 and its appearance in only the fields planted with seed from certain 

 sources suggest that the fungus is introduced with the seed. 



Anthracnose has been found prevalent in seed fields on the fruits. 

 The process of seed extraction affords ample opportunity for whole- 

 sale surface contamination of seed. The cellulose "hairs" on the 

 seed coat would afford lodgment and protection to spores. Frag- 

 ments of tissue from fruit lesions have been found among and ad- 

 herent to seeds. No evidence of the presence of dormant mycelium 

 within seeds removed from beneath deep fruit lesions has been 

 secured. 



Numerous laboratory and greenhouse tests have failed to prove 

 the presence of infectious material on commercial seed. With 

 inoculated seed, diseased seedlings result. 



Extensive field tests with treated and untreated seed, while incon- 

 clusive, indicate that the fungus is carried with the seed. 



Convincing evidence that the fungus overwinters in the field has 

 been accumulated. The disease recurs annually in certain localities 

 and not in others. In experimental fields planted with treated seed, 

 the disease reappeared in those which bore a diseased crop the 

 previous year. In extensive field tests with treated seed, 90 per 

 cent of the cases of anthracnose may possibly be thus explained. It 

 has been proved that the fungus overwinters in diseased-vine debris 

 buried in soil. 



Bordeaux sprays check but do not prevent the spread of the 

 fungus. The lower epidermis of a sprayed leaf is unprotected. 

 Spraying may be advisable in the melon, slicing-cucumber, and 

 seed-cucumber crops, but is not practicable in the cucumber-pickle 

 growing industry. 



It is believed that surface disinfection of tjie seed will eliminate 

 the infectious material. For this purpose, immersion in mercuric 

 chlorid, 1 to 1,000, for 5 minutes has been found effective and prac- 

 tically noninjurious. Disease-free seed may also be secured from 

 disease-free seed fields, and possibly by the use of old seed. 



The use of disease-free seed and a proper crop rotation to insure 

 clean soil are recommended as control measures. 



