1 8 BULLETIN 70. 
These negative results may have been due to unsuitable 
conditions. A thorough study of this phase of the disease 
will be made during the coming season. 
From a number of observations during the year, it is 
quite evident that the Alternaria which infest the onions of 
this section may also invade the foliage and produce early 
blight of potatoes. Hence it was found necessary in the 
field experiments to spray the plants with Bordeaux mix¬ 
ture as a preventive of this disease. Further observations 
may show that early blight is an important factor in pro¬ 
ducing potato failures in some sections. Should this prove 
to be true it may be controlled with Bordeaux mixture. 
Onions also frequently harbor Rhizoctonia. This probably 
explains why potatoes so frequently do poorly when planted 
in onion ground. 
Experiments during the past year indicate that sulphur 
has very little or no value in treating this disease. Lime 
may prove helpful. Both sulphur and lime will be given a 
thorough test during the coming'season. 
Preliminary experiments in rejecting all infected seed 
potatoes gave excellent results. 
ACKNOWLEDGEMENTS. 
In conclusion I wish to offer my sincere thanks to Prof. Paddock 
who has made many helpful suggestions in this work. The illustra¬ 
tions of this bulletin were all taken and arranged by him. I am also 
indebted to Mr. J. G. Coy of Fort Collins, for his co-operation in the 
field experiments. 
SUMMARY. 
Rhizoctonia solani (Kuhn) is the name given to a fun¬ 
gus which occurs on the underground parts of the potato 
plant. Our experiments show that this fungus is an active 
parasite on the potato and that it is one of the principal 
causes of potato failures in many parts of the state. 
Many potato growers are familiar with one or more of 
the following conditions which have usually been thought 
to be due to the influence of altitude or climate; abnormally 
large vines which produce few or no potatoes, (See Plate 
V.) vines which though vigorous in appearance, bear a 
large number of small, worthless tubers, (See Plates IX. and 
X.) The failure of much of the seed to grow or the dying of 
plants during the fore part of the season resulting in a poor 
stand, (See Plate III.) This fungus, in the vicinity of Fort 
Collins at least, frequently produces all of these conditions. 
The fungus lives over winter on the potatoes in the 
form of dark patches which resemble bits of soil (See Plate 
I. Fig 2.) When such potatoes are planted the fungus devel¬ 
ops with the plant and begins its attacks at once. 
