PRESS BULLETIN No. 63.
Florida Agricultural Experiment Station.
"BLACK ROOT," OR WILT DISEASE OF COTTON.
BY H. P. STUCKEY.
This disease has been identified and studied in several of the cot-
ton-growing states. As to its exact distribution in Florida, this has not
as yet been fully determined. However, the writer has visited infected
farms in Bradford and Baker counties.
HOW TO IDENTIFY THE "BLACK ROOT."
The first outward symptom of the "black root" is the wilting of the
leaves. Sometimes only one branch will show signs of the presence of
the disease, while other parts of the plantAill appear healthy and vigor-
ous. The whole plant, however, usually succumbs to the fungus and
dies within a few weeks. At other times the whole top wilts at once
and the plant soon dies. On an infected farm the plants usually die out
in spots. However, on a farm in Baker county the writer observed, in
addition to the dead spots, occasional diseased plants in almost all parts
of a large field. Further proof of the nature of the disease may be
gathered by cutting lengthwise the roots or stems of a diseased plant,
and observing the blackish-brown discoloration of the woody tissue.
Small tufts of fibrous roots will also be found on the diseased parts of the
larger roots, which is abnormal for healthy plants.
CAUSE OF THE DISEASE.
The disease is caused by a parasitic fungus (Neocomospora vasin-
fecta Var), which lives in the soil and gains entrance to the vascular
bundles of the stem through the roots. The mycelium, or vegetative
portion of the fungus, when growing rapidly, plugs up the ducts or
tubes, which carry the nourishment from the roots to the leaves of the
plant, thus cutting off the water supply from the leaves, and causing
them to wilt and die. The fungus passes the winter in the soil in the
decaying roots and stems, and probably also in the form of loose spores.
After the spores germinate and infect the plant, it will be about six
weeks before the plant will show signs of the disease.
August 1, 1907.
Prof. W. A. Orton, of the U. S. Department of Agriculture, has
fully demonstrated that the different proportions and various kinds of
fertilizers used have no direct effect in holding this disease in check; so
the farmer need not purchase an unnecessary supply of commercial fer-
tilizers with this end in view. He has also shown that treating the soil
with fungicides, such as Bordeaux mixture, lime-sulphur mixture, caus-
tic soda, formalin, etc., has not at all an encouraging effect in controlling
It is highly important that we should know the nature of this dis-
ease in order to prevent soil infection. Anything causing parts of plants
or particles of soil to be transported from one field to another is liable to
spread the disease. Therefore,rcattle should not be allowed to graze on
infected fields, and then pass over healthy or uninfected areas. Imple-
ments for cultivating, used on infected fields, should not be used on un-
infected fields. However, if their use becomes necessary, then they
should be washed with a 5 per cent. carbolic acid solution, or some
other disinfectant. Great care should be exercised in keeping the soil
of an infected field from being washed by rains into other fields. Also,
if the barnyard manure should become infected by admixture with dis-
eased plants, such manure should not be used for land intended for cot-
A judicious crop rotation will serve to hold this disease in check,
the following being recommended:
1st year.-.Corn with velvet beans between the rows.
2nd year.-Oats, followed by beggar weed.
SELECTION OF RESISTANT PLANTS.
There are to be found in every infected field some plants which
are more or less resistant to the disease. It frequently happens that of
two plants in the hill, equally exposed to infection, one will die, while
the other will mature a good crop of cotton. We should take advantage
of this fact, and when resistant plants are found in diseased spots of in-
fected fields, the seed from such plants should be saved and planted in
separate plats the following year. As some plants have greater power
for transmitting this characteristic to their offspring than others, the
seed of each resistant plant should be planted separately and their pre-
potent characteristics noted. If from this progeny the most resistant
plants are selected in a like manner, and the method closely adhered to
for a few years, the result will be a wilt-resistant strain of cotton.
State papers please copy.