May IS. 191S 



Seedling Diseases of Sugar Beets 



159 



Table VI. — Results of inoculation experiments with Rhizoctoniasp. at Garden City, Kans. 



« Two of these made feeble effort at recovery in October, showing that a little parenchyma had survived. 



The 30 beets inoculated at Rocky Ford were killed, while all the con- 

 trols remained healthy (PI. XX, fig. i). 



A consideration of the facts related indicates that soil properties are 

 potent factors influencing the susceptibility of beets to attack by Rhi- 

 zoctonia. It has long been maintained that clay soils and those which 

 are seriously deficient in organic matter and of fine, compact texture, 

 so as to bake readily, are most likely to develop Rhizoctonia diseases. 

 Further indication of this is found in the development of spontaneous 

 root-rot in the Colorado soils used in the pot experiments at Wisconsin. 

 It did not develop in the other soils employed, although the amount of 

 Rhizoctonia damping-off indicated that the Kansas soil was at least as 

 heavily infected with Rhizoctonia as was the Colorado material. The 

 experimental data lead to the conclusion, however, that, in the case of 

 the Rhizoctonia root-rot of the beet, soil temperature is a more im- 

 portant factor than soil texture. The inoculations in the field at Madi- 

 son in 1 91 2 were made at the beginning of a very hot period which en- 

 dured for several days. Infection was produced uniformly, but in 

 practically every case the beets completely recovered during the cooler 

 weather which set in a few days after the inoculations were made. In 

 191 3 infection was attempted at an earlier date when it might be ex- 

 pected that a somewhat longer period of hot weather would ensue. This 

 proved to be the case and, as already pointed out, the inoculations were 

 very generally successful. It is also significant that the cases of partial 

 or complete recovery which occur appear late in the season when the soil 

 temperatures are considerably lowered. 



PYTHIUM DEBARYANUM 



Hesse (24) reported Pythium debaryanum Hesse as a damping-ofif 

 parasite of beets in 1874, but his experimental work appears to have 

 been done on other hosts, so that while no one has doubted the accuracy 

 of Hesse's deductions, Peters (33, p. 221) appears to have been the first 

 to demonstrate by culture methods that this fungus includes the sugar 

 90271°— 15 5 



