CONTROL OF CUCUMBER MOSAIC 
9 
seasonal variation in climatic conditions. The variations in weather 
conditions during both 1923 and 1924 were duplicated at some time 
during earlier years, and the insect carriers of the disease were 
normally abundant. Furthermore, a comparison of the amount of 
mosaic in fields planted on the same land for several seasons shows 
a marked reduction in the amount of mosaic during 1923 and 1924. 
Table 2 includes all of the fields which can properly be compared 
in this regard. 
Table 2. — Percentages of mosaic in fields planted during successive seasons 
at Rockland, ^Yis. 
Field No. 
Percentage of mosaic at end of season 
1920 
1921 
1922 
1928 
1924 
2 
0) 
100 
100 
(0 
80 
100 
55 
80 
20 
(0 
60 
50 
25 
0) 
C 1 ) 
0) 
10 
85 
C 1 ) 
100 
50 
100 
20 
60 
1 

10 
1 
1 
2 

2 
3 
3 
15 
4 
5 
5 
25 
15 
8 
19 
50 
21 _. 

25 

i Field not planted to cucumbers. _ 
In the case of fields 3, 4, 5, 15, and 19, mosaic milkweeds or ground 
cherries originally were present in the fields and in some cases these 
wild hosts were so numerous that the land should not have been 
planted to cucumbers after 1921. Even under these conditions, how- 
ever, a continued effort to keep down the wild hosts resulted in a 
marked reduction in the amount of mosaic during the later years of 
the experiment. All of the evidence, therefore, seems to warrant the 
conclusion that the reduced infection was the direct result of the 
eradication of the wild hosts, particularly in view of the definite 
results obtained in similar experiments on experimental plots at 
Madison, Wis. 
EXPERIMENTS AT MADISON, WIS., 1916-1924 
Experiments with single fields at Madison, Wis., have proved 
definitely that mosaic may be controlled by the eradication of wild 
host plants and have confirmed the results obtained in the more 
extensive experiments at Rockland. The principal experiments at 
Madison were conducted on an isolated field which had been used 
for mosaic studies continuously since 1916. This plot had been 
planted to cucumbers each year from 1916 to 1923, and the field had 
been practically 100 per cent mosaic by the middle of August each 
season. Mosaic milkweed plants were abundant in the field, which 
had furnished the first evidence of infection from this host (5), 
and mosaic physalis and catnip were also present. The plot was at 
least half a mile from other cucurbits and therefore offered an excel- 
lent opportunity to test the effect of eradication, since there was no 
likelihood of infection from other fields, and the continued severity 
of the mosaic infection in preceding years furnished a definite basis 
for the interpretation of the results. 
