526 
Journal of Agricultural Research vot. xxiii. No. 1 
CONTROL EXPERIMENTS 
;The characteristic behavior, indicating that the disease is virulent 
only near the rim of the circles, encouraged the writer's attempted use 
of certain fungicides in the effort to check the spread of the fungus. 
By thoroughly saturating the soil to a depth of 4 feet with a solution 
of formaldehyde (1 part 40 per cent formalin to 100 parts water), in 
small circular areas where the activity had just started, it was found 
possible to prevent further spread of the disease. It appears that the 
fungus mycelium must extend a foot or more in advance of the last 
plant showing distress, since to be effective the soil 18 inches outside 
the apparent periphery in alfalfa fields must also be included in the 
treatment, it was found. 
With cotton plants the mycelium appears to extend for at least 2 J2 
feet in advance of the ring of recently wilted ones, there being instances 
where the disease reappeared after treatment on plants 2% feet away. 
In no case in cotton fields has the disease reappeared where the treated 
area extended as far as 3 feet outside the ring of recently wilted plants. 
The most practical method of applying the solution seems to be that of 
throwing up a small dike around the area to be treated and pouring 
in the solution gradually until the soil has been saturated to a depth of 
at least 4 feet. 
None of the areas in alfalfa fields treated as described above in July 
and early August, 1922, have shown further disease activity after 60 
days. With the control areas where dikes were thrown up, but no 
fungicide applied, the disease has progressed from 4 to feet during 
that time. There has been no reappearance of the disease outside any 
of the areas in cotton fields during 50 days after treatment. In the 
control areas the disease has advanced from 6 to 8 feet during that 
interval. 
The first successful attempt to communicate the rootrot disease to 
healthy cotton plants was made in August, 1922. The inoculation experi¬ 
ments were conducted with normal plants in the field, since it had been 
found difficult to grow normal cotton plants or develop them into a 
fruiting condition in pots in the greenhouse under the climatic condi¬ 
tions which prevail at Sacaton in summer. An area was selected on 
which there had been no evidence of rootrot since the experiment sta¬ 
tion was established in 1907. A trench was made on July 29, approxi¬ 
mately 2 feet wide, 9 feet long, and 2 yi feet deep, between two cotton 
rows in which the plants were normal in every respect and fruiting 
heavily. With a small hand pick the soil on one side of the trench was 
dug away from the roots of each plant alongside the trench until 15 
inches or more of each tap root had been exposed in the small vertical 
channels. On this side of the trench sections of rootrot-diseased cotton 
roots 1 inch in length, previously washed in distilled water, were inserted 
in the channels and placed end to end and in direct contact with the 
healthy tap root. The full length of the channel was then stuffed with 
sterile cotton soaked in distilled water, and then soil, which had been 
saturated with water, was applied with a trowel on top of the cotton 
until the channels were completely filled. 
On the other side of the trench the roots were exposed in the same 
manner, but instead of diseased roots being used the cotton wrapping was 
soaked in distilled water containing 50 cc. per liter of fresh spores col¬ 
lected from active rootrot spots. After 21 days following a rainy period, 
one of the plants treated with diseased roots wilted suddenly and upon 
