STTBOL OF CUCUMBER MOSAIC 5 
end of this season's work it was realized that it was almost impos- 
sible to procure control fields which would give a just basis for com- 
parison with fields in the experimental area. The fields used for the 
eradication experiments were all located in and about the village of 
Rockland, and any fields in the vicinity used for controls were nec- 
essarily situated at some distance in the surrounding country. It is 
a recognized fact, however, that cucumber fields located at a dis- 
tance from towns rarely suffer as severely from mosaic as do those 
which are near by, probably because of the greater number of mosaic 
host plants which occur in the vicinity of the gardens and small 
plantings which are concentrated at such points. During the five 
years of the work at Eockland it was evident that the fields situated 
a mile or more from the village rarely suffered severely from mosaic. 
After 1921. therefore, no attempt was made to use separate control 
fields as a criterion of the success of the work. The difficulties en- 
countered in controlling the mosaic during the period of 1920-1922 
demonstrated that most fields in the experimental area would be 
severely affected by mosaic under ordinary conditions and indicated 
that any marked reduction in the amount of mosaic could properly 
be considered the result of the eradication work if such a reduction 
continued during succe^ive seasons. 
MARENGO, ILL, 
The continuation of the experiments at Marengo. 111., in 1921, 
showed that the work of 1920 had greatly reduced the number of 
wild cucumber plants. Mosaic milkweeds were found at a few 
points, and mosaic infections which occurred in two fields late in 
the season were traced to this source. Very little mosaic appeared in 
the experimental area, but the disease did so little damage in the 
general vicinity that no definite conclusions could be drawn as to the 
results of the work. 
EXPERIMENTS OF 1922 
ROCKLAND, WIS. 
The experiments of 1920 and 1921 at both Rockland and Marengo 
showed that any complete eradication of wild host plants over an 
extended area offered such great practical difficulties as to make 
such a method of doubtful value to the grower under general field 
conditions. At the same time observations had shown that it was 
probable that most of the infection on the cucurbits came from 
near-by sources, although in case of the wild cucumber there is a 
possibility that the striped beetles may carry infection over con- 
siderable distances (J, 6). It appeared, however, that the chances 
of such infection were so slight as to be outweighed by the expense 
and difficulties encountered in any attempts at removing all possible 
sources of infection over a wide area. It was decided, therefore, to 
test the possibilities of controlling the disease by removing only 
such wild host plants as occurred within 50 to 100 yards "of the 
individual fields. 
The work at Rockland was carried on in this manner and all milk- 
weeds in the- vicinity of the fields were removed, whether healthy or 
affected with mosaic. A number of mosaic milkweeds were found, 
but most of them occurred at points where mosaic plants were found 
