56 BULLETIN 727, U. S. DEPARTMENT OP AGRICULTURE. 



OVERWINTERING. 



Previous references have been made to the subject of overwintering, 

 and it now remains to present the evidence relative to this phase of 

 the problem. Sheldon (46, pp. 127-137) noted that anthracnose of 

 watermelons was- more severe where the crop was grown on the same 

 ground or near the same ground used the previous year. Taubenhaus 

 (51) made similar observations in Delaware and states that a 6-year 

 rotation is thus necessitated. 



In the course of the present work, much observational evidence has 

 been accumulated during disease-survey trips, in which, however, 

 only the statements of growers were available regarding the previous 

 history of the fields. Concerning the 17 fields in which anthracnose 

 was found near Sparta, Wis., in 1915, it was learned that in the case 

 of 5 of these, cucumbers were grown on the same soil in 1914 and that 

 in the case of 3 others the 1914 crop was adjacent to the 1915 field. 

 The coldframe field near Norfolk, Va., previously mentioned, where 

 anthracnose was epidemic in 1917, was in cucumbers in 1916 and the 

 disease was present that year as well. 



At Madison, Wis., anthracnose was prevalent in fields 1 and 2 in 

 1916. In field 1 a late epidemic left numerous diseased fruits as 

 well as vines, which were plowed under late in the fall. In 1917, 

 cucumbers were again planted in these fields, as well as the four men- 

 tioned in connection with the seed treatments. Field 2 was planted 

 in part with seed treated with mercuric chlorid and in part with 

 hand-thrashed seed from cucumbers free from anthracnose. Seed 

 treated with mercuric chlorid was employed for all of field 1 except 

 for one set of plats used to test out a variety of seed treatments. 

 Among the latter were untreated control rows, but these were planted 

 with Iowa seed which was proved to be free from anthracnose by 

 the Michigan field trials previously described. The introduction of 

 anthracnose into either of these fields with the seed is therefore 

 unlikely. 



In field 2 no anthracnose developed in 1917. In field 1, where 

 much more diseased material was plowed under in 1916, anthracnose 

 appeared, not in " original centers," but as rather scattered infected 

 plants in at least three areas where diseased material was known to 

 have been abundant the year before. No anthracnose developed in 

 the three fields where treated seed was planted in soil not previously in 

 cucumbers. The recurrence of anthracnose in field 1 under these con- 

 ditions is taken as rather convincing evidence of overwintering in the 

 soil. 



In the course of inspection of the fields in the cooperative seed- 

 treatment tests it became further apparent that the disease over- 

 winters in the soil. It has been indicated in Table VIII that all of 

 the outbreaks of anthracnose among the Indiana fields planted with 



