320 
Journal oj Agricultural Research 
Vol. XXX, No. 4 
arrived did not have time to give a 
• great number of infections before dry 
weather checked the growth of the 
fungus and prevented further infec¬ 
tions and perhaps checked the progress 
of the fungus through the host tissue. 
DISSEMINATION OF THE FUNGUS 
The character of the fungus de¬ 
scribed in the previous pages points 
clearly to certain obvious methods 
whereby it may be distributed. Any 
transfer of soil from diseased fields wiil 
carry the parasite with it. In locali¬ 
ties where soil from old fields is used to 
inoculate new fields with the bacteria 
which produce the beneficial nodules 
on the roots the parasite also will be 
carried if it is present. An excellent 
example of the harm which may be 
brought about in this way was seen in 
1922 in Maryland. Soil from an old 
pea field in which the present crop was 
withering before maturity because of 
this root rot had been used to inoculate 
several neighboring fields used for peas 
for the first time. In every one of these 
fields thus inoculated individual plants 
scattered uniformly were dying, and 
others were infected, not enough in all 
to reduce the yield of this first crop 
appreciably, but enough to infest the 
soil so thoroughly that the failure of 
future crops was assured. Since trans¬ 
fer of soil from old fields to new may 
carry any of the known pea diseases 
which happen to be present, this prac¬ 
tice is so often the cause of ruin to 
crops which are grown two or three 
years after the fields have thus been 
inoculated with disease that it appears 
to produce on the whole much more 
harm than benefit. 
The flow of surface water over ad¬ 
jacent fields is an excellent conveyor of 
the fungus to new ground. The course 
which floods have taken across fields 
is sometimes indicated by areas of 
blighted peas. Irrigation water may 
be an excellent conveyor of the para¬ 
site. When the soil of an infested field 
is light and blown by wind, it may be 
a source of infestation for a large terri¬ 
tory. In this manner a few centers of 
infestation are believed by R. E. 
Vaughan, who is familiar with the 
territory, to have ruined the entire 
area of the Truax Prairies in Eau 
Claire County, Wis., for pea growing. 
In the spring of 1922 some early plant¬ 
ings of peas were visited at Rochelle, 
Ill., when a large part of the land sur¬ 
face was being prepared for planting. 
A violent wind was drying out the sur¬ 
face soil so rapidly and picking up so 
much dust from it that the whole level 
country seemed covered with a fog 
clinging close to the ground. The dis¬ 
tribution of spores with soil particles 
from a few infested fields in this local¬ 
ity under such conditions may account 
for the occasional diseased plants which 
are sometimes found when peas are 
grown for the first time in this vicinity, 
and the rather rapid subsequent in¬ 
crease of infestation. 
There is a widespread opinion among 
growers that this disease is often intro¬ 
duced into new fields by the use of in¬ 
fected pea seed grown in diseased fields. 
This opinion, however, does not ap¬ 
pear to be justified. Since the fungus 
does not enter the plant above the 
ground, it never reaches the seed and 
could only become attached to the seed 
in particles of dust from the soil. Even 
though this might conceivably happen, 
it appears to be a remote possibility, 
and, in any case, very few of the spores 
which could withstand drying would 
be present, so few that they would al¬ 
most certainly escape detection by any 
experimental method that could be 
used and, therefore, so few that the 
disease which they would produce 
would not become conspicuous until 
several successive crops of peas have 
been grown. Although it is impos¬ 
sible to say that new infestation never 
takes place in this manner it appears 
to be at least a rare occurrence. 
CONTROL MEASURES 
CROP ROTATION 
Although from early times the tradi¬ 
tion of pea growing warns of failure 
which will attend the planting of peas 
on the same ground repeatedly, and 
English experience has developed a 
rotation of five or six years’ duration 
as an insurance against disease, there 
are, on the other hand, so many 
advantages in intensive culture of the 
crop for the commercial purposes for 
which it is chiefly grown in the United 
States that rotation has usually been 
adopted only when the failure of the 
crop made this course necessary. A 
long rotation has been found to have 
a number of disadvantages of more or 
less importance. In some localities 
experience has abundantly shown that 
the second crop of peas on new land 
thrives better than the first, and the 
third may produce a better crop than 
either of the preceding. Peas grown 
for canning can often be produced 
more cheaply in a limited area close 
to the canning plant than in the much 
larger territory required by a long 
rotation. In the pea-seed-growing dis- 
