BACTERIAL, WILT OF CUCURBITS. 



9 



found in this locality. Referring to the beetle curve for the hibernating brood (fig. 3), 

 it will be seen that on June 14 and again about June 21 there was sl sudden drop in the 

 number of striped beetles. On looking over the daily notes after plotting this curve, 

 it was found that on June 13 the beetles were so numerous a3 to threaten total destruc- 

 tion to the young plants, and an application of a dust insecticide and lime mixture was 

 made to all the plants in the field. Just before the second drop in the curve the first 

 Bordeaux and lead-arsenate spray treatment of the season had been carried out, and 

 in addition the same insecticide had been applied to all control plots. At the same 

 time that the number of beetles decreased in Fields II and Ila a decided increase was 

 noted in Field IV, about a quarter of a mile distant. In Fields II and Ila the max- 

 imum wilt came just after a period of heavy rain and high humidity, while in Field II 

 and one other field during 1915 the maximum wilt came just before the period of 

 heaviest rainfall and after 

 a period of comparatively 

 low humidity and rainfall. 

 Again the relation be- 

 tween beetle and wilt 

 curves holds, the one fol- 

 lowing the other at an in- 

 terval of about one month. 



During the same season 

 (curve not plotted; records 

 of the number of beetles 

 and the amount of wilt 

 were also kept for two 

 other experimental fields 

 in East Marion. In Field 

 I (fig. 1) the maximum of 

 the beetle curve occurred 

 about June 28 and that of 

 the wilt curve about Au- 

 gust 1. In Field IV the 

 maximum of the beetle 

 curve occurred near June 

 26 and the wilt maximum 

 about July 27. 



During the season of 

 1916 the records at Gies- 

 boro Point, D. C. (fig. 5), 

 showed this same relation. 

 In Field XI, planted 

 about April 25, the maxi- 

 mum of the first brood of beetles occurred June 12, while the maximum of wilt preva- 

 lence came exactly one month later. In another of our experimental fields (XVI; 

 the maximum of the beetle curve came between June 15 and 20, while the corre- 

 sponding wilt-curve maximum occurred about July 21. Here the first planting was 

 made April 25, but only a few seeds came up and most of the vines were from a second 

 planting made May 21. The month preceding the period of maximum wilt preva- 

 lence had been very dry, with only light showers, but this period was immediately 

 followed by several days of heavy rain, during which time the downy mildew 

 obtained a foothold, so that after July 28 no additional wilt records could be kept. 



Partial records in this locality were also kept for about a dozen other fields of cu- 

 cumbers, cantaloupes, and varieties of summer and winter squashes. While the data 

 for complete graphs of both beetles and wilt are not available in these last cases, the 

 142179°— 20— Bull. 828 2 



Fig. 5. — Map of a portion of Giesboro Point, D. C, where wilt-sequenee 

 records were kept during the spring of 1916. The rornan numerals 

 show the location of the fields; the arabic numerals show the sequence 

 of the wilt. 



