CONTROL OF CUCUMBER MOSAIC 13 
Mosaic is transmitted from the wild cucumber to the cultivated 
cucurbits by the striped beetle, Didbrotica vittata, and to a lesser 
extent by the 12-spotted beetle, D. 12-punctata. The melon aphis, 
Aphis gossypii, acts as the chief agency of dissemination from the 
other wild host plants. 
The experiments included groups of 8 to 17 fields in localities 
where mosaic had been prevalent in previous years. In the earlier 
experiments, attempts were made to remove all the mosaic host plants 
occurring in areas of one-half to one square mile. It was later found, 
however, that it was apparently equally effective to confine the eradi- 
cation to those hosts which occurred in or within 50 to 75 yards of 
the individual fields, since most of the mosaic infection on the wild 
hosts occurred in the vicinity of land which had previously grown 
mosaic cucurbits. Under this system all the plants of known host 
species were removed regardless of the occurrence of mosaic. The 
eradication was begun at the time cucumbers were planted and the 
inspections were repeated at intervals of 10 to 15 days during the 
season. 
The fact that the mosaic infection on the perennials such as the 
milkweed and Physalis spp. occurred almost entirely on land which 
had grown cucumbers indicated that they had originally been in- 
fected from the cultivated cucurbits and emphasized the importance 
of rotation of the crop. It was also evident that it is essential to 
keep the fields free from such hosts in order to prevent their becoming 
infected with "mosaic and acting as sources of infection to succeeding 
crops. Where the shoots of these hosts were pulled out rapidly 
throughout the season it was found that they practically disappeared 
by the end of the second year. 
The experiments of 1920 to 1922, conducted in both Illinois and 
Wisconsin, were inconclusive, due partly to a lack of sufficient mosaic 
infection in the Illinois trials and to the constant discovery of new 
hosts during the early part of the work. In 1923 and 1924 the ex- 
periments were continued only at Rockland, Wis., where all the 
known hosts were abundant excepting the pokeweed. The results 
of these years showed that cucumber mosaic can be controlled by 
this method under difficult field conditions. The average infection 
in the Rockland area during the period from 1920 to 1922 was ap- 
proximately 39 per cent, while in 1923 and 1924 it was reduced to 
slightly more than 3 per cent. 
Similar experiments were conducted on a single field at Madison, 
Wis., in which 100 per cent of mosaic had occurred each year from 
1916 to 1922. In 1923^ and 1924, following the eradication of mosaic 
milkweeds and physalis, the percentage of infection was reduced to 
approximately 10 per cent during both seasons. 
In view of these results it is believed that cucumber mosaic can be 
controlled by the methods outlined in this bulletin, if the work is 
done with care and continued throughout the season. 
