July 1,1925 Overwintering and Dissemination of Cucurbit Mosaic 
41 
Other Insects 
The only other insects which have been tested as possible carriers 
of poke weed mosaic are the striped and 12-spotted Diabrotica beetles. 
In experimental trials with these insects the writers have found no 
evidence which indicates that they are agents in the transmission of 
mosaic from the pokeweed, but the work so far has been of a limited 
nature. Both insects have occasionally been found feeding on the 
pokeweed and are often found between the young leaves at the tip of 
the plants, although there is little evidence to indicate any extensive 
feeding on this host. At present the available evidence does not 
indicate that they are important factors in transmitting the disease 
to the cucurbits. 
IMPORTANCE OF THE POKEWEED AS A SOURCE OF INFECTION TO THE CUCURBITS 
In Wisconsin and northern Illinois the pokeweed is of little im¬ 
portance in overwintering cucurbit mosaic because of its rare occur¬ 
rence. Up to the present the writers have never found pokeweed 
plants in the vicinity of cucumber fields in Wisconsin. In south¬ 
western Michigan, however, mosaic pokeweeds have been observed 
in the vicinity of cucumber fields in Allegan, Berrien, Ottawa, and 
Van Buren Counties. The disease has been noted in abundance by 
W. W. Gilbert in the vicinity of Donaldson, Ind., where cucumber 
mosaic is also common. M. W. Gardner, of the Indiana Agricultural 
Experiment Station, reports that mosaic pokeweeds are abundant in 
the vicinity of melon fields at Vincennes, Ind., where cucurbit mosaic 
has been serious for some time. In the summers of 1922 and 1923 
one of the writers visited fields of cucumbers at Anna, in the extreme 
southern portion of Illinois, which had suffered severely from mosaic 
for several seasons. Pokeweed plants were found to be numerous 
along the roadsides and in fence rows about the fields. At least 50 
per cent of the plants observed were affected by mosaic, and in many 
cases they occurred within a few feet of cultivated cucurbits. As 
the pokeweed appears to be a potential source of infection to the 
cucurbits, the observations in the Anna district indicate that the 
opportunities are far greater for infection from this host than in any 
of the localities where the milkweed and wild cucumber are apparently 
responsible for overwintering mosaic. 
The occurrence of such extensive infection on the pokeweed was 
of special interest, as neither the wild cucumber nor the milkweed 
seemed to occur in the locality. A careful search revealed only one 
group of plants of Asclepias syriaca } and these were at a distance of 
some miles from cucumber plantings and were free from mosaic. 
No wild cucumber plants were found in the vicinity and the local 
growers seemed unfamiliar with both the wild cucumber and milk¬ 
weed. Gardner also reports that he has seldom seen either the 
wild cucumber or milkweed in southern Indiana. As these hosts 
are not common in the vicinity of Anna, it seems probable that 
the mosaic infection on the cucurbits is traceable to the mosaic 
pokeweeds in the vicinity of the fields. Further observations have 
made this theory seem more probable, since mosaic pokeweeds have 
been found growing in hotbeds which contained young cucumber 
plants ready for setting out in the field. These pokeweeds were so 
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