Jan. 6,1923 
A Phytophthora Footrot of Rhubarb 
23 
In a large commercial field there would be no need for spraying the 
entire plantation unless the widespread occurrence of the disease indi¬ 
cated this need. Application could be confined to those plants in the 
immediate vicinity of spots where the disease definitely occurred the 
preceding season. Consequently, a small machine, such as a knapsack 
sprayer or a small pressure sprayer (which was used by the writer), is 
satisfactory under ordinary circumstances. 
In addition to the spraying, to prevent infection of plants near those 
definitely attacked by the fungus, the observance of sanitary precau¬ 
tions is exceedingly important. Diseased plants should be dug up and 
destroyed, with all the dead parts found lying on the ground. Every 
vestige of the large fleshy roots showing the presence of decay should be 
removed. Then a heavy application of formaldehyde of the usual 
strength for soil sterilization, 1 part commercial formalin to 100 parts of 
water, should be made to the hole where the plant stood. To replant 
rhubarb without this sterilization would be a waste of time, for the new 
plant could not be expected to live through the season. Repeated ob¬ 
servations have shown this to be the case (p. 2, text and footnote). In 
a field in which control measures have not been taken, cultivation may 
spread the disease along the row. In fact, this appears to be one of the 
means by which spread occurs. Long vacant spaces in the rows in 
which the disease has occurred indicate this. 
This disease is undoubtedly spread widely by means of the root divisions 
in the ordinary commercial propagation and distribution of rhubarb. 
To prevent this, one should be sure that his roots have come from a 
field in which the disease does not occur, or at least from a clean portion 
of the field. If this can be relied upon, no further measures will be nec¬ 
essary. Where there is a strong chance that roots have come from dis¬ 
eased fields, examination and occasional cutting with a sharp knife will 
disclose the presence of actual decay in the roots if it exists. Such roots 
should be discarded. A thorough wetting of suspected roots with formal¬ 
dehyde i to 100, followed by covering them with burlap bags or canvas 
for several hours, is a still further measure against starting the disease 
in a new field. A careful experiment by the writer showed that this is a 
very effective method of killing most of the surface fungi on the roots 
and that it does not injure the roots for propagating. Rhubarb when 
dormant is very hardy and will endure rather extreme conditions of cold, 
drying, chemical treatment, or other unfavorable conditions. 
SUMMARY 
(1) A disease of rhubarb, caused by Phytophthora parasitica var. rhei, 
is reported for the first time. The causal organism is distinctly different 
from one mentioned by Beach on the same host. 
(2) Its distribution has not been determined. It has definitely been 
found in Maryland, District of Columbia, and Virginia. It is probably 
much more widely spread. 
(3) The disease is primarily a footrot and rootrot of the rhubarb plant, 
resulting in its rapid and complete destruction. 
(4) Warm, wet weather over a considerable period appears to be 
requisite to the development of the disease. 
(5) The organism is readily isolated and grown in pure culture, though 
special methods of isolating are sometimes required. 
(6) Inoculation experiments are described, in which the plants were 
almost invariably killed by the fungus. Reisolations were made. 
