Angular leaf spot (blackfire)
 Weather fleck

Title: Common leaf diseases of flue cured tobacco
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066877/00001
 Material Information
Title: Common leaf diseases of flue cured tobacco
Series Title: Plant Pathology fact sheet 15
Physical Description: Book
Creator: Kucharek, Tom
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Plant Pathology Department -- Institute of Food andAgricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1981
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066877
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 51338413

Table of Contents
        Page 1
        Page 2
    Angular leaf spot (blackfire)
        Page 3
    Weather fleck
        Page 4
        Page 5
        Page 6
        Page 7
Full Text

Plant Pathology Fact Sheet

Common Leaf Diseases of Flue Cured

Tom Kucharek, Professor and Extension Plant Pathologist, University of Florida,
Gainesville. 1981; Revised February 2001.
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean


Tobacco is susceptible to numerous dis-
eases, and almost all diseases will result in
some sort of leaf symptoms. Black shank, root
knot nematodes, and other diseases that cause
malfunctions of roots and lower stems will
cause leaf discoloration indirectly, usually in
definite patterns on leaf margins and between
major veins. Discoloration results when water
and nutrient transport from the soil is impeded.
Diseases included in this publication, are those
that cause damage to the leaf directly by infect-
ing the leaf itself, thereby causing distinct spots,
blights or mosaic patterns. Spots may be aggre-
gated (grouped) or randomly dispersed de-
pending on the organism.

Three types of organisms cause leaf dis-
eases that occur commonly on tobacco in
Florida: First, fungi are organisms without chlo-
rophyll, with microscopic spores and with mi-
croscopic threads called hyphae. Numerous
spore types can be produced. Those involved
with infection are called sporangia or conidia,
and are produced in abundance. Blue mold can
produce millions of sporangia on a leaf. The
size of one of those spores is 1/900 of an inch.
Secondly, bacteria are microscopic organisms
that are simple rod-shaped cells that reproduce
by divisions of cells. Bacteria which cause plant
diseases lack chlorophyll, and generally are
about 1/12,000 of an inch long. Thirdly, viruses
mentioned herein are non-cellular and are com-
posed of protein and nucleic acids only. They
reproduce in living plant cells by redirecting
cellular functions of the plant. An average to-

bacco mosaic particle is 1/90,000 of an inch
Blue Mold

Blue mold is caused by the fungus
Peronospora tabacina In the United States blue
mold is a problem only on tobacco. Blue mold
had been considered to be primarily a prob-
lem in the plant bed where total loss of plants
has occurred when not controlled. However,
since 1979, blue mold has become epidemic in
the field in the United States in some years.
Extremely wet and cool conditions provide fa-
vorable conditions for fungus development,
spread, and infection. Spore production can
occur from 46-86F. Temperatures above 860F
or below 460F restrict spore production. The
time from infection to sporulation is typically
from 4 to 15 days, but can be considerably
longer depending upon day and night tempera-
tures, variety, and strain of the fungus. Night
temperatures from 50 to 650F and daytime tem-
peratures from 70-85F are ideal for disease de-
velopment. It is important to remember that
during most years in Florida ideal temperatures
for blue mold occur during much of the early
part of the tobacco growing season. Thus, rain-
fall and irrigation tend to strongly influence
blue mold.
Blue mold causes variable symptoms. In
young plants, leaf yellowing and cupping oc-
cur (Fig. 1). Eventually leaves will turn brown
and the plant may die. In the plant bed some-
what circular patches of plants will be infected,
with disease spread away from these areas. As
plants get larger, various degrees of systemic
infection can occur.


Prior to the time of stem elongation af-
ter transplanting, a severe systemic infection can
occur. Leaves become distorted and yellowed
(Fig. 2). Vascular discoloration in the form of
brown streaks, can occur as well as excessive
suckering (Fig. 3). Where infection occurs on
established, growing plants in the field, leaf
spots of various sizes and shapes occur. Usu-
ally the spots begin with a yellow area and then
turn brown (Fig. 4). Fresh sporulation will ap-
pear white to grey-blue (Fig. 5). As the fungus
ages, the downy growth will become light
brown in color and is located primarily on the
lower leaf surfaces.

CONTROL of blue mold can be accom-
plished with chemical and cultural methods.
For chemical control, contact your county Ex-
tension agent for up-to-date recommendations.
Cultural controls include: (1) Use transplants
produced in northern Florida; preferably grow
your own plants in open non-shaded areas.
Plants from south Florida grown outdoors used
to be commonly infected with numerous dis-
eases including blue mold. Greenhouse-pro-
duced plants in south Florida in recent years
have had no blue mold. (2) Do not seed the
transplant bed prior to January 10. The use of a
plastic cover maintains heat for accelerated
plant growth, and temperatures above 86F in-
hibit blue mold development. (3) Avoid use of
excessive amounts of nitrogen. (4) Irrigate beds
when needed. Excessive irrigation will create
favorable conditions for blue mold especially
when coupled with high rainfall amounts. (5)
Inspect fields and beds routinely. Inspect near
high trees, hedge rows and low areas as blue
mold usually begins in such areas first. (6) De-
stroy old plants in the bed immediately after
successful transplanting is complete. Cut and
plow down stalks in the field immediately af-
ter harvest. Plow down reduces inoculum of
several diseases for the following season.
Brown Spot

Brown spot is caused by the fungus Al-
ternaria alternate. Tobacco is considered to be the

only host for this fungus, although tomatoes,
peppers, and certain weeds have been infected
in some experiments. Brown spot occurs on
plants in the field primarily from topping time
through the harvesting period. Brown spot can
occur from 59 F 860F. Wet weather is condu-
cive for disease development. Brown spot le-
sions occur primarily on lower leaves, progress-
ing to upper leaves. Suckers, petioles, seed cap-
sules, and stems may become infected in some
situations. Spots begin as a pinpoint area with
a tan center, surrounded by a brown ring. A
yellow halo may also be evident at this time.
Later, the spot enlarges up to 1 1/2 inches in
diameter at which time concentric rings are seen
within the brown spot (Fig. 6). A diffuse yel-
low area usually surrounds the spot. The yel-
low area is caused by a toxin produced by the
CONTROL of brown spot is achieved
by growing a vigorous, well-fertilized, healthy
plant. Brown spot is more apt to be a problem
on poorly managed tobacco. Specifically, low
potassium levels, nematode injury and other
harmful factors make plants susceptible to in-
fection. The use of proper rates of MH for sucker
control reduces brown spot. Delayed flower
stalk removal (topping) can result in increased
amounts of brown spot. If brown spot becomes
a serious threat, advance harvesting of lower
leaves to minimize loss. A few varieties have
some resistance to brown spot.

Frogeye Leaf spot

Frogeye leaf spot is caused by the fungus,
Cercospora nicotine. Typically, it has not been a
disease of commercial importance in that it
occurred late in the season in Florida. In fact,
some people equate the presence of frogeye leaf
spot with ripe and quality tobacco. Frogeye leaf
spot is more likely to be common on later-ma-
turing tobacco. However, in recent years, frog-
eye leaf spot has increased to damaging levels
in some plantings. If tobacco were grown
through the latter part of the summer, frogeye
leaf spot could be a problem. Frogeye can oc-

cur in leaves at any time during the season.
Spots vary in size from a pinpoint to slightly
over 1/2 in. Spots 1/8 to 1/4 inch are com-
mon. Frogeye leaf spots are sunken, somewhat
round, white in the center when mature and de-
lineated by a distinct brown-purple border ring.
The ring may encompass most of an individual
spot in some situations (Fig. 7). No controls are

Angular Leaf spot (Blackfire)

Angular leaf spot is caused by the
bacterium, Pseudomona syringae pv. angulata.
Tobacco is considered to be the primary host
for this bacterium, but numerous other plant
species (cowpeas, soybean, tomatoes, pep-
pers) have been infected experimentally. This
bacterium can survive in tobacco stubble, dry
leaf, or manufactured tobacco. It survives also
on roots of pasture, weed, and crop plants
such as tobacco, wheat, rye, barley, vetch,
chickweed, shepherds purse, lespedeza,
clover, ragweed, and oxalis. Spread of the
bacterium occurs primarily by wind-driven
rain, rain splash, or irrigation. Infection of
leaves occurs through wounds or natural
plant openings such as stomates. Bacterial
cells enter into such openings and within 2 7
days, leaf spots develop. The shorter incuba-
tion period of two days occurs when plants
are exposed to excess rain or irrigation. Angu-
lar leaf spot can develop at any temperature
suitable for growth of tobacco. Symptoms of
angular leaf spot are often diagnostic in the
field (Fig. 8). Distinct angular, dark, vein-
limited spots occur on a leaf, often in an
aggregated pattern. Laboratory diagnosis
may be necessary in many situations.
CONTROL of angular leaf spot is
difficult but certain measures used collec-
tively will reduce this disease: (1) Rotate the
plant bed and field sites with pasture crops.
(2) Plow down plant bed and field sites
during the previous fall so that plant roots are
well decomposed. (3) Use disease-free trans-
plants. (4) Avoid high amounts of nitrogen or

lime as these materials predispose tobacco to
infection. (5) Cut down and plow down plant
beds and fields immediately after harvest.

Viral Diseases

Tobacco mosaic virus (TMV), Potato vi-
rus Y (PVY), Tobacco etch virus (TEV), Tomato
spotted wilt virus (TSWV) and Cucumber Mo-
saic virus (CMV) occur in tobacco in Florida.
All five viruses can infect numerous other hosts
including peppers, tomatoes, eggplants, pota-
toes, black nightshade, and numerous other
weed and crop species.
Incubation of TMV may take 2-3 days for
fast-growing plants. Numerous other variables
can influence the length of the incubation pe-
riod. The incubation period for PVY is about 7
days. The incubation period for TEV can vary
between 4 to 10 days.
Symptoms of TMV may be masked at
temperatures above 800F or below 500F. Spread
of TMV is primarily mechanical. Plant sap from
an infected plant, if moved via people or equip-
ment to a healthy plant, can spread this disease.
Thus, any kind of field operation can cause
spread of TMV. TEV, PVY and CMV are spread
primarily by aphid feeding. Aphids may be
wind-borne or fly to a field from adjacent fields
or hedge rows. Aphids in a field may have origi-
nated many miles from your field. Five seconds
of feeding is all that is necessary for the aphid
to attain or transmit the virus. This is why in-
secticide sprays are not recommended for vi-
rus control; the aphid can transmit the virus
before being killed.
Viral symptoms are variable and posi-
tive identification in the field is not recom-
mended. Tobacco mosaic virus usually appears
as an overall checkering (variegation) of shades
of greens and yellows (Fig. 9). Plants are often
stunted when infected with TMV. Potato virus
Y often results in a vein-banding symptom (Fig.
10). Tobacco etch virus often has white to brown
etchings as one of the symptoms (Fig. 11). CMV
causes stunting, severe leaf narrowing and leaf
puckering and distortion (Fig.12). For informa-

tion on Tomato spotted wilt virus (TSWV), see
University of Florida Circular 914.
CONTROL of viruses on tobacco is dif-
ficult. However, certain controls should be used
on a routine basis: (1) Grow your own trans-
plants; transplants produced outdoors in south
Florida are often infected with virus. (2) Elimi-
nate weed hosts such as ground cherry, black
nightshade, or jimsonweed. (3) Isolate tobacco
fields from plantings of peppers, tomatoes,
potatoes, or eggplants. (4) Do not allow aphids
to become established in transplant beds. (5)
Do not use tobacco products prior to or during
field operations associated with tobacco. (6) Do
not prune roots when cultivating. (7) Use crop
rotation. (8) Do not top plants obviously in-
fected with TMV; rogue them when they first
appear and do not handle other plants after
doing so. (9) Cut, disk, and plow down fields
and transplant beds immediately after harvest-
ing. Recently some varieties have been devel-
oped that possess resistance to PVY, TEV or
TMV. Recently, a couple of pesticides have
been labeled that suppress development of

Weather Fleck

Weather fleck is caused by toxicants in
the air, with ozone being the primary agent.
Ozone is a natural component of our atmo-
sphere. However, ozone can originate by ultra-
violet radiation reacting with certain pollutants
arising as exhausts generated from engines,
furnaces, or other mechanical devices. Ozone
enters plants through stomates (breathing
pores) occurring on either side of a leaf surface.
Senescing or rapidly expanding leaves are less
susceptible than younger leaves. Damage will
tend to be most severe on turgid (swollen)
leaves due to heavy rains, irrigations, poor
drainage, high humidity, or other variables that
increase turgor pressure (water pressure)
within the plant. Symptoms include white to
tan etching on leaves (Fig. 12). These symptoms
can be confused with virus symptoms.
CONTROL is achieved primarily by
avoiding excess moisture situations, by good
drainage in the soil, and by avoidance of
excessive irrigation.

Figure 1. Blue mold in tobacco seedlings. Figure 2. Systemic blue mold in transplanted

Figure 3. Inner stem symptoms
blue mold.

;ure 4. Leat spots caused

Figure 5. Sporulation of blue m

Figure 9. Tobacco mosaic virus. Figure 10. Tobacco mosaic virus and potato
virus Y.

Figure 12. Cucumber mosaic virus

Figure 11. Tobacco etch virus.

Figure 13. Weather fleck.

i. ..

University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs