BACTERIAL WILT OF CUCURBITS. 
9 
Potomac River 
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 a 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 as 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 Ha 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-sequence 
records were kept during the spring of 1916. The roman numerals 
show the location of the fields; the arabic numerals show the sequence 
of the wilt. 
