CONTROL OF CUCUMBER MOSAIC 7 
This fact was of particular interest, since Gardner and Kendrick 
(7, 8, 9,) had shown that these same species of Physalis were 
important factors in the overwintering of tomato mosaic. 
In the eradication experiments of 1923, therefore, an attempt was 
made to remove all wild physalis plants in the vicinity of the cucum- 
ber fields at Rockland,' together with all milkweeds and wild cucum- 
bers. It was found, however, that the work of the previous seasons 
had resulted in practically eradicating the latter host in the vicinity 
of most of the fields. A large number of perennial physalis plants 
were found, however, many of which were affected with mosaic. 
These plants presented more difficulty in their removal, as they were 
usually small and when intermixed with other weeds were not easily 
located. Eleven fields were included in the experiments of 1923. A 
trace of mosaic appeared in two cucumber fields on July 11 and the 
mosaic plants were removed, together with a few suspected plants 
in other fields. No more mosaic was found until the inspection of 
July 31, when one field showed 10 per cent. In this field, which 
was somewhat isolated, the disease spread with considerable rapidity, 
but it did not develop in the other 10 fields until late in the season. 
On August 27 the badly infected field showed 60 per cent of mosaic, 
whereas the remaining 10 fields showed an average infection of less 
than 10 per cent. A comparison of fields planted on the same land 
in 1922 and 1923, as shown in Table 2, indicates the striking reduc^ 
tion in the amount of mosaic during the latter season. 
The season of 1923 was abnormally dry, which checked the growth 
of new shoots of both milkweeds and physalis plants and thus fav- 
ored the work of eradication. The seasonal conditions, however, did 
not seem to be responsible for the apparent control of the disease, 
since a normal number of aphids and cucumber beetles were present 
in the fields, and the rapid progress of the disease in the single field 
mentioned above was evidence that the agencies of disease transmis- 
sion were present. It seemed probable, therefore, that the sudden 
reduction in the amount of mosaic in 1923 was partly due to the 
cumulative effect of the eradication of the wild cucumber and milk- 
weeds from 1920 to 1922, together with the removal of the previously 
unsuspected mosaic physalis. It was felt, however, that the results 
must be repeated before they could safely be ascribed as entirely 
due to the removal of the wild hosts. 
EXPERIMENTS OF 1924 AT ROCKLAND, WIS. 
The same area was used at Rockland in 1924, but 14 fields were in- 
cluded in the experiments. A large number of mosaic physalis 
plants were again found, but the milkweeds and wild cucumbers had 
practically disappeared. No mosaic developed in any of the fields 
until July 30, when two fields showed a trace of the disease. On 
August 19 four fields showed from 15 to 40 per cent of mosaic, but 
the remaining fields were practically free from the disease, the aver- 
age infection for all fields being 11 per cent. A severe hailstorm 
destroyed six of the fields during the latter part of August, so that 
complete data could not be obtained after that date, but a later in- 
spection of the remaining fields showed that the disease had done 
little damage after the inspection of August 19. 
