58 



BULLETIN 72*7, U. S. DEPARTMENT OF AGRICULTURE. 



other is the fact that in one of the Wisconsin fields, where the disease 

 occurred in 1914, 1915, and 1916, no anthracnose could be found in 

 1917 when treated seed was used. 



Table IX. — Relation between lack of crop rotation and the occurrence of cucumber 



anthracnose, season of 1917. 





Number of 

 fields. 



Fields used for cucumbers in 1916. 



Seed used. 



Number. 



Anthracnose in 1917. 





Number. 



Percent- 

 age. 





73 

 75 



14 



7 



9 



6 



64 





85 







Total 



148 



21 



15 



71 







As to the mode of overwintering and the possibility of a perfect 

 stage nothing definite is known. Using soil collected from a dis- 

 eased field in October, Carsner 1 secured seedling infection in Febru- 

 ary. He also secured seedling infection in sterile soil with which 

 were mixed chopped-up diseased vines previously kept in storage 

 for five months. Potebnia (38, p. 82) left diseased host parts out of 

 doors over winter but failed to find an ascus stage. 



In the fall of 1916 diseased vines and fruits of various hosts were 

 placed in wire cages and left on the ground in the garden over winter. 

 On April 11, 1917, 14 samples of soil were taken in sterile pots from 

 under these cages. Treated seed was planted in these pots, but no 

 anthracnose appeared on the seedlings. Examination of some of the 

 overwintered material in the cages on March 29 failed to show the 

 presence of spores, and no development of the anthracnose fungus 

 occurred under damp chamber conditions. More work should be 

 done 'along this line. 2 



The present status of the problem is, then, that field observations 

 and tests prove that the fungus overwinters in the field, although the 

 exact mode of this overwintering is unknown. 



CONTROL. 



Consideration of the control of anthracnose may be conveniently 

 divided, so far as this work is concerned, into two categories, spraying 

 and seed treatment combined with crop rotation. 



1 Carsner, E. Op. cit. 



Sin the fall of 1917 diseased cucumber vines were buried in a small flower garden in Lansing, Mich., 

 where anthracnose had never been present. In the summer of 1918 treated cucumber seed was planted 

 in this spot. On August 4, 37 out of 68 plants were diseased with anthracnose, many dam ping-off with the 

 disease. This proves that the fungus overwinters in the old diseased vines in the soil. Furthermore, 

 treated 1916 seed was planted in 1918 in a 2-acre portion of the Michigan seed field which had borne a badly 

 diseased crop in 1917. Anthracnose made its appearance at numerous and scattered points in this field 

 in 1918, thus further proving that the fungus overwinters in the soil. 



