Mar. io, 1923 
Rosette Disease of Wheat and Its Control 
783 
oped in 92 per cent of the plants in the pails containing undisinfected soil. 
In the disinfected soil all plants were healthy and remained so during 
the season. 13 Plates 5, B, and 6 show the photographic evidence ob¬ 
tained from this experiment. 
The second experiment consisted of two plots, A and B, each 4 by 6 
feet in size, surrounded by wooden frames made of pine boards three- 
fourths of an inch in thickness and 8 inches wide. These frames were 
sunk in the soil 4 inches, leaving a 4-inch wall above the soil to keep out 
surface water (PI. 5, A). 
The soil inside these frames was heavily infested, like that used in the 
first experiment. In plot A, the dry surface soil was removed and a 
three-fourths-inch layer of the subsurface soil was removed and kept 
separate and not disinfected. The remaining soil was then removed 
from both frames to a depth of 10 inches, after which it was replaced in 
thin layers which were saturated with the formaldehyde solution pre¬ 
viously described. Care was taken to return the soil layers in the same 
order as they were removed so that the original strata might be main¬ 
tained as nearly as possible. After the disinfection the plots were al¬ 
lowed to air and dry for five weeks, after which the undisinfected layer 
of infested subsurface soil was returned to the surface and seed trenches 
of plot A. Then Harvest Queen (white-chaffed Red Cross) seed from a 
field free from the rosette disease was sown in rows 6 inches apart in 
both plots. Good germination was obtained and the resulting plants 
were very robust in the fall, showing no signs of rosette disease. In the 
spring essentially the same results were obtained as in the first experi¬ 
ment—that is, in plot A a high percentage of disease occurred, while 
plot B was essentially healthy. In the latter plot, however, a very few 
diseased plants developed around the edge, due doubtless either to 
splashing of water or seepage, or both, from the infested soil outside, 
indicating that the causal factor was disseminated to a slight extent 
in some such manner, apparently in the soil water. Apart from these 
few diseased plants, the plants in plot B were healthy and robust, 
remaining so throughout the season (PI. 7, B). Plot A, which received 
the infested soil before seeding, developed the disease in about 75 per 
cent of the plants (PI. 7, A). 
Wheat growing in the infested soil just outside these plots developed 
from 85 to 95 per cent of rosette disease. 
These results seem to prove conclusively that the rosette disease is 
caused by some factor other than winter conditions, soil type, or im¬ 
proper drainage; and, in view of the conclusions drawn in connection 
with soil factors other than parasitic, it seems that the evidence points 
most strongly in the direction of a causal organism or perhaps to some 
virus which may be greatly influenced by formaldehyde. 
ANIMAL PARASITES 
Insect parasites have been considered the cause of rosette disease by a 
number of investigators other than entomologists. A number of ento¬ 
mologists have examined plants affected by the rosette disease, and all 
have expressed the idea that insects are not the cause. In order to 
accumulate definite evidence on these points investigations have 
been conducted cooperatively by the writer and W. H. Larrimer of the 
Bureau of Entomology, United States Department of Agriculture. The 
results of these investigations will be published in a separate paper. 
13 Similar experiments carried on later with steam-sterilized soil gave the same results. 
