2l6 
Journal of Agricultural Research 
Vol. XXVI, No. S 
(6) Two field experiments were conducted in naturally infested soil 
located in the American Bottoms of the Mississippi River near Granite 
City, Ill., opposite St. Louis, Mo. 
(7) The results of all the experiments show that the Helminthosporium 
disease as it occurs on the underground parts of wheat and barley is 
influenced by soil temperature and soil moisture. 
(8) The disease developed at all temperatures used between the 
extremes of 8° and 35 0 C., but infection was greatly reduced toward the 
extremes. 
(9) The optimum soil temperature for the disease on Marquis (spring) 
wheat and on Hanna and Hannchen (spring) barleys was found to be 
28° C. For Harvest Queen (winter) wheat the optimum was 32 0 C. 
(10) There was some shifting in the optima of the several experiments, 
but it was limited to the high temperatures. This shifting is explained 
on a basis of other factors than moisture which were not uniformly 
controlled throughout all of the experiments. A control of such uncer¬ 
tain factors will make possible a more accurate determination of the 
temperature optima in future experiments. 
(n) The disease seems to attack barley more freely than wheat at 
temperatures below 16 0 C. 
(12) In all experiments Marquis wheat has shown the highest sus¬ 
ceptibility to the disease. 
(13) An experiment was conducted to determine the influence of 
controlled alternating soil temperatures on the disease in comparison 
with a constant temperature equivalent to the mean of the alternating 
series. 
(14) Essentially the same amount of disease developed at the soil 
temperatures which alternated between 14 0 and 30° C. every 12 hours 
as developed at the constant mean temperature of 22 0 . 
(15) These results are preliminary and represent but one simple com¬ 
bination of time and temperatures, and, therefore, should not be given 
too wide an application. However, they do indicate that the constant 
temperature method probably gives a fair index to the influence of soil 
temperatures under field conditions. 
(16) Two soil-moisture experiments conducted in the greenhouse show 
that high soil moistures favor the disease. A third moisture experiment 
combined with a soil-temperature series also shows that high soil moisture 
is more favorable to the disease at temperatures of 24 0 C. and above. 
(17) The results of this combined soil moisture and temperature experi¬ 
ment indicate that the temperature optimum is not altered by changes 
in soil moisture, whereas changes in soil temperature do seem to cause a. 
rather regular shifting in the soil moisture optimum. The temperatures 
at and above 24 0 C. favor a high moisture optimum, while temperatures 
below 24 0 C. seem to favor low moisture optima. 
(18) Two field experiments show that there is a direct correlation 
between soil temperature and soil moisture and the development of the 
disease. Early-sown winter wheat is more severely affected by the 
disease than late-sown winter wheat. These results are in direct line 
with the controlled experiments conducted in the soil temperature tanks 
since early sowings are subjected to higher soil temperatures than are the 
late sowings. 
