Circular 190 January 1959
AGRICULTURAL EXTENSION SERVICE
Angular Leafspot of Tobacco
J. H. OWEN, F. CLARK, and S. L. BROTHERS*
Professor of Plant Pathology, College of Agriculture;
associate Agronomist, Agricultural Experiment Station;
and Assistant Agronomist, Agricultural Extension Service
i) the University of Florida, Gainesville, Florida.
Fig. 1.-The disease on the mature tobacco leaf, showing
typical dark, angular lesions.
The angular leafspot disease of tobacco is
caused by a bacterium, Pseudomonas angulata
(Fromme & Murray) Holland, which may infect
tobacco in any stage of growth from seedlings to
mature plants, producing small, dark, angular-
shaped lesions on the leaves. This disease is com-
mon in most flue-cured tobacco growing areas.
It was first reported in Florida in 1957 on mature
plants in several fields near Newberry and Mayo,
and in 1958 it was again destructive on mature
plants in these areas. It occurred also in several
fields in Madison, Hamilton, Suwannee and Colum-
bia counties. The abundance of rainfall during
the 1957 and 1958 seasons was very favorable
for the establishment and development of this
The bacterial organism which causes the dis-
ease is capable of spreading rapidly once it be-
comes established, and there are possibilities that
this disease could appear in Florida fields in wide-
spread proportions during seasons of heavy rain-
fall. Therefore, flue-cured tobacco growers should
be familiar with the symptoms of this disease and
the precautions that should be taken to control
it in the plant bed before infected plants are trans-
planted into the fields.
Angular leafspot usually appears first rather
suddenly, within 4 to 5 days following rainy
periods, in the wetter parts of the plant beds on
tender, rapidly growing plants. On the young
plants the bacterial organism enters the leaves
during periods of high humidity, producing water-
soaked spots which rapidly turn brown to almost
black, giving the plant a scorched appearance.
Normally, only a few angular dark-brown spots
appear on any one leaf of a seedling. Some leaves,
however, may become severely infected, and the
tissue around the spot will often appear puckered
or torn on rapidly growing plants.
The early stages of angular leafspot appear as
angular-to-irregular, black water-soaked tissue
which dies rapidly, forming dark-brown, angular
lesions (Fig. 1). The centers of these spots often
become light tan with dark borders as they age,
and during rainy weather the dead centers may
fall out. A slight yellowing or chlorosis is some-
times observed as a narrow band around the spot.
These angular-shaped lesions range in size from
1/25 to 1/3 inch in diameter and frequently co-
alesce, thus involving large areas of the leaf blade.
When numerous infections appear, the leaf may
become distorted. Dark brown lesions may ap-
pear on the seed capsules.
Outbreaks of angular leafspot on mature
plants in the field will develop rather suddenly
on rapidly growing plants which might previously
have appeared to be free of infection. If this
disease is suspected, on plants in the plant bed
or in the field, contact your county agent imme-
diately for proper identification.
The disease can be expected to be more de-
structive and widespread during seasons with pro-
longed rainy periods. During dry seasons or years
of moderate rainfall it will likely be absent or
cause little damage. In 1957, the disease was
first observed on the lower 8 to 10 leaves of field
plants 3 feet tall after several days of intermit-
tant rains, one of which was a hard 3-inch rain-
fall. During the following two weeks of dry
weather, the disease appeared to be checked. With
the recurrence of several days of rainy weather,
including two heavy rainfalls of 2.25 and 1.19
inches, the disease continued to spread up the
plants, causing severe infection. The rainfall dur-
ing the 1958 flue-cured tobacco season in Florida
was probably one of the heaviest on record, and
again angular leafspot was severe in several loca-
Inspection of an old plant bed in the vicinity
of an infected field revealed that the plants left
in the plant bed also were heavily infected. This
indicated that the bacterial organism might have
been introduced on contaminated seed or on plant
tissue among the seed.
SOURCE OF THE DISEASE
The bacterial organism which causes angular
leafspot has been introduced into the plant beds
and fields from a number of sources. It has been
shown that it is seed-borne, and contaminated
seeds are a common source of the pathogen. The
debris from the seed capsules and pieces of in-
fected leaf tissue mixed with the seed could har-
bor the bacterium, or it might survive from one
season until the next on used plant bed covers. It
also is capable of living over on diseased plant
parts left in fields or plant beds from the previous
season. Under certain conditions the organism
may remain over in the soil. There has been some
indication that it can survive from season to
season on the roots of grasses and weeds.
During periods of rainy weather or heavy dews
the bacteria exude and accumulate on the surface
of the spots, and are readily spread to other plants
by splashing or wind-borne rains. Hard rains
sometimes produce a water-soaked condition of
the leaf tissue which is easily invaded by the
organism, and an increase in infection usually
follows rains and windstorms. Field laborers
working among diseased plants while dew or mois-
ture is present may spread the bacteria to other
plants and possibly from field to field. There is
little chance, however, that the organism will
spread in nature from field to field when fields are
separated by several hundred feet or more.
The bacteria may be transferred readily from
one plant bed to another on the hands of workers
while weeding or pulling plants. Infected plants
convey the bacterium from the plant bed into the
field where the disease will continue to develop
if rainy weather persists. The disease may like-
wise be spread from one farm to another on in-
FACTORS AFFECTING SEVERITY
Rainfall.--The disease is more severe during
prolonged wet seasons. Rainfall also is the chief
means of disseminating the bacterium in the field
once it has become established. In addition, it
causes a faster growing and more succulent plant
which is more susceptible to bacterial infection.
It may not be present during dry seasons.
Fertilization and Topping Practices.-Low
topping and high-nitrogen fertilization favor dis-
ease development. Under certain conditions, low
potash increases susceptibility of the tobacco
plant to infection. Any factor which will increase
the succulence of the tissue also increases sus-
ceptibility to the pathogen.
Harvesting and Curing.-When tobacco leaves
infected with the angular leafspot bacterium are
harvested and cured they result in a poorer qual-
ity of tobacco than non-infected leaves. Angular
leafspot lesions are frequently invaded by the soft
rot bacteria as secondary organisms which con-
tinue to develop during the curing process and
might cause additional losses unless proper pre-
cautions are taken to provide adequate ventila-
tion and heat during the yellowing of the leaves.
A yellowing temperature of 1000F. with good
ventilation, or maintaining a humidity of 85 per-
cent in the curing barn, has greatly improved the
quality of the leaf whenever brown spot and soft
rot diseases were present.
The control of angular leafspot can best be ob-
tained by the production and use of disease-free
seedlings. Attempts should be made to reduce
infection in the plant bed. Proper field sanitation
also should be practiced.
Seed Treatment.-The bacterium has been
proven to be carried on the seed as a contaminant.
If there is some question as to whether the seeds
are contaminated with the bacterium or come
from an area where the disease is common, they
can be treated easily. The treatment to use is
corrosive sublimate bichloridee of mercury), 1
part in 1,000 parts of water used in a glass or
earthenware container. The seeds may be placed
directly in the treating solution, or they can be
tied in a cheesecloth bag and soaked in the solu-
tion for 15 minutes, rinsed thoroughly in water,
and dried at room temperature. Corrosive sub-
limate should be handled with care, since it is
poisonous. It does not, however, injure the skin.
It may be obtained from most drug stores. Your
county agent may know where it can be purchased.
Plant Bed Sanitation.-Seed treatment alone
cannot control the disease and should be accom-
panied by certain sanitary practices.
The plant bed location should be new, or if
the same bed is used, the soil and side boards
should be treated with methyl bromide gas or
steam to insure freedom from the angular leaf-
spot bacterium. Plant beds should be well ditched
. id drained to prevent water from flowing over
It is most desirable that new cloth be used on
the plant bed each year, particularly if angular
leafspot was present the previous year.
Handling of the plants should be kept at a
minimum, and care should be taken to prevent
spread of infection from an infested plant bed to
a clean one by workers at transplanting time. If
diseased seedlings appear in the plant bed, the
plants should not be handled or pulled while they
The purchase or exchange of seedlings should
be avoided unless they are known to be free of
angular leafspot, or have been sprayed or dusted
as a precautionary method to control this disease.
If the disease appears in the plant bed, its
spread to other seedlings may be prevented or
minimized by the application of bactericidal
sprays or dusts. Antibiotics such as "Agrimycin
100" and "Streptomycin" have been reported to
be effective controls for this disease. Drenches
and sprays of tribasic copper sulphate have also
given satisfactory results.
Agrimycin 100 (15.0% Streptomycin and 1.5%
Terramycin), or Streptomycin at a concentration
of 200 ppm, is applied to the seedlings in the
plant bed as a spray at the rate of 10 gallons per
100 square yards. Three applications at weekly
intervals should give good control.
Streptomycin may also be applied in the form
of a dust of 1,000 to 4,000 ppm, at a rate of three
to four pounds per 100 square yards. Four ap-
plications are required at weekly intervals.
Tribasic copper sulphate (fixed copper), 3
pounds per 100 gallons of water, can be applied
as a drench at a rate of 25 gallons per 100 square
yards using a sprinkling can. Two applications
a week apart are recommended. This same cop-
per mixture may also be used as a spray at 10
gallons per 100 square yards, using 4 weekly
applications. Copper drenches or sprays have
been shown to be less effective than either Agri-
mycin or Streptomycin. The first application or
the spray or dust should be made when the plants
are in the two-leaf stage.
Field Sanitation.-Practice rotation to prevent
growth of tobacco on the same land for two con-
secutive years. This will decrease the possibility
of the bacterium being carried over in the soil.
Avoid handling the crop while the leaves are
wet, if the disease is known to be present.
If the disease begins to develop in the field,
an antibiotic spray should be helpful. This is
expensive, however, and control is difficult, par-
ticularly if the disease has become well estab-
lished and rainy weather occurs. Agrimycin 100
or Streptomycin at 200 ppm, 120 gallons per acre,
has been found to check the spread of the disease
to some extent in the field.
Clayton, E. E. Tobacco Diseases and Their Control. U.
S. Dept. Agr. Farmer's Bul. 2020, p. 69. 1950.
Fromme, F. D., and S. A. Wingard. Blackfire and Wild-
fire of Tobacco and Their Control. Va. Agr. Exp. Sta.
Bul. 228, p. 19. 1922.
Owen, J. H., and F. Clark. Angular Leafspot of Tobacco
in Florida. U. S. Dept. Agr. Plant Dis. Reptr. 41:
Shaw, L., and G. W. Thorne, Jr. Wildfire Control Studies
in Burley Tobacco Plant Beds in North Carolina in
1955. U. S. Dept. Agr. Plant Dis. Reptr. 40: 325-327.
Wolf, F. A. Tobacco Diseases and Decays. Duke Univ.
Press, Durham. 396 pp. 1957.
COOPERATIVE EXTENSION WORK IN
AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and
United States Department of Agriculture, Cooperating
M. O. Watkins, Director