CONTROL OF CUCUMBER MOSAIC 6 
in the experimental section. Seven other fields at some distance 
from the town were considered as controls on the work. The experi- 
ments at Rockland presented peculiar difficulties, as the fields, in 
many cases, were so closely adjacent to one another that the disease 
was likely to spread with great rapidity after it once appeared. It 
was felt, however, that if the disease could be controlled under these 
circumstances the method would prove practicable in nearly all 
localities. 
In 1920 approximately 2,500 wild cucumber plants were removed 
at Rockland, about 50 of which showed mosaic. The greater number 
of plants were found along the LaCrosse River, which bounded one 
side of the experimental area, and along certain other small streams. 
Most of the mosaic plants, however, occurred in and about the village 
and in several cases were close to fields of cucumbers. The 10 ex- 
perimental fields remained free from mosaic until about July 15, 
although some of the control fields showed the disease. On August 
5, however, two fields were found to be severely affected with mosaic. 
The disease appeared to spread from these fields to others in the 
vicinity, and on August 31 the average infection in all fields was 80 
per cent. Investigations showed that the fields first affected con- 
tained large numbers of mosaic milkweed plants which were in- 
fested with the cucumber aphis. As a result of investigations during 
1920-1921 (^, J), it was found that the milkweed, Asclepias syriaca 
L., was a perennial host of cucurbit mosaic, and it was evident that 
it must be included in the program of eradication. (PL 2, B.) 
MARENGO, ILL. 
In experiments at Marengo, 111., in 1920, the fields were so scattered 
that it was necessary to include an area of more than 1 square mile 
in the work of eradication. Most of the land was under cultivation, 
however, and attention was centered on small streams, fence rows, 
and the vicinity of farm buildings. The number of wild cucumber 
plants was few when compared with the Rockland area, but several 
mosaic plants were found near farm buildings. The fields in the 
experimental area remained practically free from mosaic throughout 
the season, although fields in the vicinity were severely damaged by 
the disease. 
PLYMOUTH, IND. 
A similar experiment was conducted at Plymouth, Ind., in 1920, 
through the cooperation of M. W. Gardner, of the Indiana Agricul- 
tural Experiment Station. The work there covered an area of about 
1 square mile, containing four cucumber fields. A few wild cucumber 
plants were found, but none showed signs of mosaic. A few mosaic 
plants appeared in two of the fields at the end of the season, but no 
serious losses had occurred. 
RESULTS OF WORK IN 1920 
The results of the work at Marengo seemed to show a distinct 
reduction in the amount of mosaic as a result of the removal of wild 
cucumbers. Although no mosaic hosts were found at Plymouth, the 
results there indicated that the disease might not occur to any extent 
in districts where the wild cucumber was rare. The results at Rock- 
