10 
BULLETIN 1461, U. S. DEPARTMENT OF AGRICULTURE 
In both the 1923 and 1924 experiments the first eradication was 
made between June 12 and June 15, shortly before planting, and the 
field and vicinity were then regularly inspected every three to seven 
days until August 25. 
In 1923 the disease did not appear in the field until August 19, and 
only 7 per cent of the plants were affected on September 7. In 1924 
the results were much the same, as only 12 per cent of the plants were 
affected on September 1. As shown by Table 3, these figures are in 
sharp contrast with the early and severe infection which occurred 
during the six preceding years. 
Table 3. — Effect of eradication of wild hosts on occurrence of mosaic in 
experimental plot at Madison, Wis. 
Date of 
first in- 
fection 
Percentage of mo- 
saic late in season 
Date 
observed 
Year 
No 
eradica- 
tion 
Eradica- 
tion 
1916. 
July 7 
July 19 
80 
100 
Aug. 9 
1917 
Aug. 19 
19181 
1919 
July 8 
July 12 
July 17 
June 29 
Aug. 19 
Aug. 20 

100 
100 
100 
100 
Aug. 13 
1920 
Aug. 16 
1921 
Aug. 21 
1922 
July 30 
1923. 
7 
12 
1924 „ 
Sept. l 
i In 1918 severe infection was reported but was not observed by the writers. 
Similar results were also obtained during 1924 and 1925 with 
another plot which had formerly grown mosaic cucurbits. This field 
was severely damaged by mosaic for three years previous to 1924, 
the infection being between 60 and 80 per cent each season. In this 
experiment a number of mosaic milkweeds and wild cucumber plants 
were removed about the field, and these measures were again fol- 
lowed by the practical elimination of mosaic. No infection occurred 
in 1924, and in 1925 only 3 per cent of the plants showed mosaic on 
August 21. In this experiment a control plot was planted in 1924 
at a distance of one-third of a mile on land on which severe mosaic 
infection had occured in 1919, 1920, and 1922, and where mosaic 
milkweeds were known to occur. This control plot was 100 per cent 
mosaic on August 15. In all these experiments there was the normal 
infestation of insect carriers throughout the season. In view of these 
definite results, the belief that cucumber mosaic can be controlled by 
the eradication of the wild host plants of the disease appears to be 
justified. 
EXPERIMENTS AT ANNA, ILL., 1923 
In addition to the foregoing experiments, preliminary work was 
undertaken in the vicinity of Anna, 111., in the extreme southern 
portion of the State, in 1923. The pokeweed, Phytolacca decan- 
dra L., which is known to be a perennial host of cucumber mosaic, 
but which does not occur commonly in Wisconsin (5), appeared to 
be the only known host of importance in this section. Mosaic poke- 
