FOOT-ROT DISEASES OF WHEAT IN AMERICA o7 
Stevens (67) reports one experiment dealing with the influence 
of temperature on the growth of Helminthosporium sativum which 
indicated that the optimum temperature is near 25°C. Paxton (54) 
reports that the optimum temperature for growth is near 30° C., 
but does not state the number of experiments on which this conclusion 
is based. 
The variations between the results obtained with presumably the 
same species of fungus might be explained on a basis of some strain 
differences. However, as the writer has obtained variations in the 
optima of different experiments he feels that experimental error 
may be the most logical explanation for the variations reported. 
CONTROL OF HELMINTHOSPORIUM FOOT-ROT 
While exact control measures have not been worked out for this 
disease, there are certain general recommendations which may be 
made. Since the spores of the fungus are carried on the seed, the 
ordinary methods of surface disinfection will control infection from 
this source. This method, however, is not likely to bring satisfac- 
tory results in most cases, because much primary infection of seed- 
lings originates from mycelium borne internally in the seed and also 
from the fungus which persists in the soil. 
Practically no work has been done to determine the best method 
for killing the mycelium of Helminthosporium sativum in wheat 
seeds. Atanasoff and Johnson (3) found that subjecting barley seed 
infected by this fungus to a dry-heat treatment (95° to 100° C.) 
for 30 hours practically controlled primary seedling infection when 
the treated seed was sown in uninfested soil. Their experiments 
were extended to wheat seed to determine the effect of these high 
temperatures on germination, and they found that good viable seed 
withstood the treatment surprisingly well. Certain of the newer 
organic mercury compounds which have been used (59, 69) to treat 
cereal seed seem to control or reduce the injury produced by certain 
parasites occurring in the seed, but in no case have these treatments 
been used to determine their control value for the disease caused by 
H. sativum. In general, seed treatments will tend to reduce the ex- 
tent of primary infection, but they will not control infection when 
the parasite occurs in the soil. Since the latter condition generally 
exists when the disease is prevalent, effective control measures must 
include the consideration of the soil phase. As in the case of seed- 
treatment methods, however, very little has been done to combat the 
disease from the standpoint of soil infestation. 
The application of general sanitary measures should control the 
disease to some extent, but just what success may be expected in this 
direction can not be predicted at this time. As pointed out earlier 
in this bulletin, the fungus apparently persists for a considerable 
period in the soil, even though the land may le in summer fallow. 
Just what influence different cropping systems may have on the 
disease can not be stated until further work has been done along 
this line. Preliminary experiments indicate that the growth of 
the fungus used by the writer is favored by a neutral to slightly 
acid medium, but no information is at hand concerning the influence 
of soil reaction on the development of the disease. The influence of 
various fertilizers on the development of the disease is likewise 
undetermined, ? 
