8 BULLETIN 1461 ? U. S. DEPARTMENT OF AGRICULTURE 
SUMMARY OF RESULTS AT ROCKLAND, WIS., 1920-1924 
The results of 1924, together with those of 1923, show what ap- 
pears to be an actual control of cucurbit mosaic through the removal 
of wild host plants. Table 1 gives a comparison of the losses from 
mosaic in the experimental area from 1920 to 1924, and it will be 
seen that the damage during the last two seasons was of little eco- 
nomic importance. The actual losses from mosaic were less than 
is indicated by the field averages, since the fields varied in size from 
V 8 to iy 2 acres and in man y cases the heaviest mosaic infection in 
1923 and 1924 occurred in the smallest fields. When comparison is 
made on the basis of total plants infected with mosaic, it will be 
seen that the loss in 1923 and 1924 was negligible. 
Table 1. — Percentage of mosaic in cucumber fields in experimental area at 
Rockland, Wis., 1920-1924 
Date observed 
Number 
of fields 
in area 
Average 
percent- 
age of 
mosaic 
per field 
Percent- 
age of 
total 
plants in 
area 
affected 
with 
mosaic 
Aug. 31, 1920 . 
12 
17 
18 
13 
14 
80 
20 
41 
6 
11 
65 
Aug. 24, 1921 
15 
Aug. 24,1922 
37 
Aug.27,1923 . . 
2 
Aug. 19, 1924 
5 
The results of 1923 and 1924 are the only ones which can properly 
be considered as t} T pical of the possible results from the eradication 
of wild host plants at Eockiand, since our knowledge of the number 
of wild host species was increased each year during the period from 
1920 to 1922. When the work was begun in 1920 it was supposed 
that the wild cucumber, Micrampelis lobata, was the only wild host 
to be feared. The work of that year, however, showed that the milk- 
weed, Asclepias syriaca, was even more important at Rockland than 
the wild cucumber. During 1921 and 1922 a further study of the. 
situation showed that two perennial wild species of ground cherry, 
Physalis subgldbrata and P. heterophylZa, were also a means of over- 
wintering mosaic, and at Madison it was also found that the catnip, 
Nepeta cataria L., was occasionally infected with the disease (5, 10). 
The work of 1923 and 1924 was based on the removal of these plants 
together with a further survey for other wild hosts of the disease. 
So far, no other perennial host plants have been found in this region, 
and the results of the last two seasons indicate that those mentioned 
above are the chief sources of mosaic infection in the section about 
Rockland. The success of the work of 1923 and 1924 was partly a 
result of the earlier experiments, since the previous eradication work 
had practically eliminated all mosaic milkweed and wild cucumber 
plants and at the same time extended our knowledge of the host 
range of the disease. 
The reduction in the amount of mosaic seems directly attributable 
to the removal of wild host plants about the fields rather than to 
any abnormal reduction in the number of insect carriers or to any 
