Mar. 17,1923 Influence of Soil Temperature on Seedling-Blight 
865 
The first two sowings showed the influence of high soil temperature upon 
both host and parasite. The germination and stand of the controls was 
greatly reduced, yet the reduction in germination and stand from blight 
was not as great as in the following two sowings where the mean soil 
temperature was 16 0 C. The last seeding, however, in which the seed 
germinated in a cool soil, gave little blighting, and, further, the stand and 
general vigor of the plants were comparable to the condition of the 
controls. 
These soil-temperature experiments in the field have shown, then, that 
wheat germinated in a cool soil resists the blight but when germinated in 
a warm soil succumbs to the attack. These results also have shown that 
the critical soil temperature for the production of the seedling-blight of 
Fig. 14.—Graph showing relation of date of planting to the development of seedling-blight of com in 1921. 
The seedling-blight occurred during the April plantings when the mean soil temperature was below 2o°C. 
No blight developed when the mean soil temperature reached 20 0 C. (Summary of fig. 2.) 
wheat is the same under field conditions as in the soil-temperature tanks 
in the greenhouse, namely, about 12 0 C. 
These results already have been applied as control measures by agrono¬ 
mists and other wheat growers, yet further emphasis is necessary from 
the phytopathological viewpoint. Seeding at the earliest safe date 
in the spring for spring wheat and the latest safe date in the fall for 
winter wheat is the best method of reducing the seedling-blight. Agron¬ 
omists have shown that the date of planting has a marked relation to 
lodging and to yield and quality of grain. The marked reaction between 
the date of seeding and tie root development may partly explain those 
relations. 
