36 BULLETIN 1347, U. S. DEPARTMENT OF AGRICULTURE 
in case the fungus gains entrance. However, this method is not 
applicable in some cases, as, for example, in parts of Kansas where 
Ophiobolus graminis and Helminthosporiwm sativum sometimes ap- 
pear in the same wheat fields, and in parts of Wisconsin, Minnesota, 
and the Dakotas where Gibberella saubinetu and H. sativum appear 
together. As indicated in Figure 2 (p. 13), infection by O. graminis 
is favored by fairly low soil temperatures, whereas infection by A. 
sativum is favored by fairly high soil temperatures, and on the 
basis of the studies reported by Dickson (78) the optimum soil tem- 
perature for wheat-seedling infection by G. saubinetiz les between 
the temperature optima for O. graminis and ZH. sativum. From these 
data it is evident that any arrangement of fall or spring seeding 
dates for the purpose of obtaining soil-temperature differences will 
result in very little economic benefit to the farmer when any two or 
more of these parasites occur together. Plainly, if the temperature 
conditions are not favorable for one disease they are likely to be so 
for one of the others, as is shown by the curves in Figure 2. 
Several investigators have attempted to control foot-rots by means 
of special cropping and soil-tillage systems and also through the use 
of fertilizers and amendments. Although these methods of control 
have not been thoroughly developed for any of these diseases, there 
is good reason to believe that, in certain regions at least, they offer 
one of the most promising means of reducing crop losses due to 
foot-rots. 
The development of varieties resistant to foot-rots has not been 
given systematic consideration by many plant breeders, and there- 
fore very little definite knowledge on this subject is at hand. Several 
investigators -have mentioned varieties as being resistant to certain 
foot-rots, but in some cases varieties said to be resistant by one 
worker are reported highly susceptible by another. In general, it 
may be stated that most wheat varieties seem to be susceptible to one 
or another of the foot-rots when the proper conditions for infection 
exist. 
Numerous attempts have been made to control foot-rots by treating 
the soil with chemicals which kill the parasites present. In some 
cases the results have been successful, but in most instances the 
materials used were too expensive for general field use. This mode 
of attacking plant parasites which live in the soil has not been 
studied systematically. Low-priced chemicals have not been inves- 
tigated, nor have the methods of application been studied. This 
method should be efficient for the control of such foot-rots as take-all 
when they are not too extensively distributed over a field. How- 
ever, it appears doubtful whether this method would ever be prac- 
ticable for the control of the Helminthosporium foot-rot, owing to 
the wide dissemination and copious occurrence of the spores of the 
parasite. 
On the basis of our present knowledge it is clear that the control 
of the foot-rots depends not on one method but on several.’ 
14 The following publications on the wheat foot-rots were received after this bulletin 
was prepared for the printer: 
Dosdall, Louise. Factors influencing the pathogenicity of Helminthosporium sativum. | 
Minn. Agr. Exp. Sta. Tech. Bul. 17, 47 pp. illus., 1923. 
Guyot, L. De l’existence de formes pycnidiennes chez Ophiobolus graminis, Sacc., et 
Map herpotrichus (Fr.) Sace. Jn Rev. Path. Vég. et Ent. Agr., t. 12, pp. 74-81, 
illus., 25. : 
