BACTERIAL WILT OF CUCURBITS. 19 



of rather cool weather during early June they had at this time (June 29) attained a 

 height of only 2 to 4 inches with two to four true leaves developed. 



The following day, June 30, seven cases were found in two half-acre commercial 

 fields (V) of cucumbers planted May 15 (not in cucurbits in 1915) and 19 cases in a 

 large garden plat of cucumbers and squashes (XII) likewise planted May 15 (possibly 

 in cucurbits the preceding year). 



The next cases of wilt were found July 11 in our experimental Blocks II and Ila 

 (Ila was not in cucurbits in 1915). These blocks were first planted on May 8, but on 

 account of ccld, damp, weather and a consequent poor stand they were replanted 

 June 13. 



Cucurbits were planted in experimental Blocks I and III on June 21, and wilt first 

 developed here July 20. 



In all these instances wilt started from beetle-injured leaves. 

 Subsequent cases developed in similarly injured plants and more or 

 less in widening circles around the original centers. 



The record at Giesboro Point, D. C, covered an area approximately 

 one-half by three-quarters of a mile in extent, bounded on one side 

 by the Potomac River and on three sides by woods. (Fig. 5=) 



Up to June 1, 1916, no wilt had appeared within this area. At the next date of 

 observation, June 3, one case of wilt was found in a cantaloupe field planted May 10, 

 one case in a crookneck-squash field planted about May 1, and three and six cases, 

 respectively, in two cucumber fields planted April 20 to 25. At least three of these 

 fields were not in cucurbits the preceding season. Pure cultures of Bacillus trachei- 

 philus were obtained from several of these plants. 



On June 6 one plant began to wilt in a cymling field planted April 20 to 25 and not in 

 cucurbits during 1915. 



On June 13 seven plants began to wilt in a cymling field planted about May 15 and 

 not in cucurbits during 1915, and four cases developed in cucumber plants outside the 

 wire-covered insect cages in the experimental field where the main part of the stand 

 was planted May 31. Wilt was very prevalent in this field during 1915. 



At the time of the next observation, June 23, wilt was becoming rather prevalent 

 in all the fields where wilt had occurred before the middle of the month, and many 

 cases were also found in four other fields. 



Observations throughout the season on wild cucurbits (Sicyos angulatus) growing 

 abundantly along the Potomac shore failed to show any signs of bacterial wilt, although 

 a few striped cucumber beetles were now and then found feeding upon the leaves. 

 On two occasions a slight but general wilting was noted during a hot sunny day on 

 plants growing in the sand high up on the shore. The wilting was plainly due to 

 excessive transpiration in a dry soil. However, plates were poured from several of 

 these plants and a microscopical examination also was made. There was in no case 

 any evidence of bacterial invasion. 



During the spring of 1917 a similar set of observations was made in 

 a locality near Tuxedo, Md. On account of the press of other work 

 the records were not quite as complete, but the results were entirely 

 in line with those obtained in the two preceding localities. 



It should be noted with regard to the bacterial wilt in these three 

 localities that in all cases the leaves first showin.g volt in the spring 

 had typical cucumber-beetle injuries, that the wilt had plainly started 

 from these injured points, and that in many of the fields such beetle 

 injuries had not at this time become general. 



