Plant Pathology Department, University of Kentucky

Diagnostic Images

Tobacco

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Last Modified: 01-Apr-2008
Copyright © 2004, University of Kentucky, College of Agriculture, Department of Plant Pathology

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Target spot
Causal agent: basidiospores of the fungus Thanatephorus cucumeris (anamorph Rhizoctonia solani )
Signs: none seen with naked eye.
Symptoms: When the fungus first infects the leaf, it produces a dark green spot. As the infection process continues,
the spots turn papery thin and can drop out. Spots can also enlarge and have a bull's eye look to them.
The last image shows infection of older plants in the field.
Total image number: 13

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Damping-off
Causal agent: Rhizoctonia solani (fungus)
Signs: webbing of fungus (mycelium)
Symptoms: Plants usually rot at the soilless mix surface and continue to rot until the entire plant dies.
Plants were on a floatbed system.
2nd row of images are fungal hyphae.
3rd row, the single image shows infected plants in a float tray.
Total image number: 7

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Sclerotinia collar rot
Causal agent: Sclerotinia sclerotiorum (fungus)
Signs: black, raisin-like, resting structure of fungus (sclerotia). See 2nd image from left.
Symptoms: Plants usually rot at the soilless mix surface and continue to rot until the entire plant dies.
Plants were on a floatbed system.
In the 2nd row, the image shows a large number of plants in a group rotted by the disease.
Total image number: 5

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Black shank
Causal agent: Phytophthora parasitica var. nicotianae
Signs: spore-producing bodies ("sporangia") seen after infected tissue placed in water culture
Symptoms: Plants wilt, turn yellow and eventually die
Total image number: 21

4 images of plants in the field with symptoms of the disease called "Black shank".

2 images of plants in the field with typical 'disking" symptoms in the infected pith tissue.

8 images of leaves with symptoms of the disease "Black shank" in this case called "Foliar Black shank".

7 images of the "signs" of the fungus: asexual spore-producing bodies called "sporangia" of the fungus Phytophthora parasitica var. nicotianae. When the sporangia is hollow-looking it has produced zoospores and they swam away in search of susceptible host tissue.
The last 3 images show zoospores swimming out of a sporangium.

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Root rot
Causal agent: Pythium spp. (fungus)
Signs: Images of the asexual spore-producing bodies ("sporangia") of a species of Pythium.
In the 1st row shows views of oospores outside and inside root tissue.
In the 2nd row, shows a view of the fungus in water incubation. The first two images on the left show filamentous
sporangia and a single terminal sporangia. The third image shows a filamentous sporangium.
The last image on the right show spores in the act of swimming away from a terminal sporangium.
In the 3rd row, the image on the left shows plants that are stunted and yellow due to the disease.
The image on the right is a demonstration with healthy plants on the left and artificially-inoculated plants on the right.
Symptoms:
Total image number: 10

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Blue mold
Causal agent: Peronospora tabacina (fungus)
Signs: visible "mold" which is the fungus producing spores in infected areas.
Symptoms: yellow spots on upper leaf surface with corresponding moldy growth on lower leaf surface
1st row of images are seedling plants, burley tobacco.
2nd row of images are leaves from tobacco growing in the field, burley tobacco.
Total image number: 8

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Fusarium wilt
Causal agent: Fusarium oxysporum f. sp. nicotianae (fungus)
Signs: none
Symptoms: A one-sided yellowing when looking at the whole plant, an individual leaf, or both.
Vascular disoloration is also seen.
Total image number: 8
1st row of images is of burley tobacco in the field.
2nd row of images is of burley tobacco cultivar, 'KT 204', from a field.

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Angular leaf spot
Causal agent: Pseudomonas syringae p.v. tabaci (bacterium)
Signs: see two images at the right; the bacteria can be seen oozing from the infected leaf tissue.
Symptoms: Images below are of dark tobacco. On dark tobacco the spots have a little bit different look on dark
tobacco because you do not usually see the yellow halo you will see on burley varieties, although a grouping of
spots can cause an area of the leaf to turn yellow. Also interior portions of the spots look darker
than those on burley.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Tomato Spotted Wilt
Causal agent: Tomato Spotted Wilt Virus (virus)
Signs:
Symptoms: The 1st row of images is of a small burley plant showing leaf symptoms.
2nd row shows 2 small burley plants with none or minimal leaf symptoms, but severe stem symptoms.
3rd row shows an older burley plant with leaf symptoms.
4th shows older burley plants with leaf and stem symptoms.
5th row shows older dark plants with leaf and stem symptoms.
6th row shows a plant in the field with TSWV symptoms which may be confused with Fusarium wilt.
Total image number: 20

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Tobacco streak (suspected)
Causal agent: Tobacco Streak Virus (virus)
Signs:
Symptoms: It is characterized by striking patterns of necrotic leaf tissue usually bearing a close relation to the veins. Some leaves may be affected on one side only. Midribs have dead streaks and the small veins are darkened. Stalks can show depressed dead areas. Apparently normal-growing plants develop necrosis, puckering, and curling of the young leaves. Affected plants appear permanently injured and likely to die; this severe stage soon passes, however, and the plants resume apparently normal growth, with only the originally affected leaves being misshapen and dwarfed.
1st row images are of dark tobacco leaves.
2nd row shows infected plant in the field.
Total image number: 5

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Tobacco ringspot (suspected)
Causal agent: Tobacco Ringspot Virus (virus)
Signs:
Symptoms: Images are of burley tobacco leaves.
In the 1st row of images, the characteristic "oak leaf" pattern is evident on leaves at far left and center. In the 2nd row, the single leaf shows this "oak leaf" pattern. This virus is carried to the plant by the dagger nematode, Xiphenema americanum. The first symptoms may appear on tobacco in the plant bed or on plants
soon after they are set in the field. The virus may overwinter in many biennial and perennial weeds from which it may
be transmitted to tobacco. Tobacco crops that follow clover, soybean, lespedeza and alfalfa are particularly likely to
show ringspot infection, as these crops may act as inoculum (virus) sources. In the field infected plants may appear
alone or in clusters. Most infected plants recover as new symptomless leaves develop.
Total image number: 6

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Alfalfa mosaic
Causal agent: Alfalfa Mosaic Virus (virus)
Signs:
Symptoms: Images are of a burley tobacco plant.
It is characterized by chlorotic line patterns somewhat similar to the symptoms of tobacco ringspot virus,
but with severe symptoms causing younger leaves to appear nearly white with puckering of tissue
between the veins.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: fertilizer injury
Causal agent: 10x rate of fertilizer in floatbed system
Signs:
Symptoms: Reading on Dist4 meter (dissolved solids tester) indicated about a 10x rate of fertilizer had been used
and likely caused the yellowing and necrosis of the older leaves and along the margins of the younger leaves.
The plants are a dark tobacco variety 'VA 359'.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Weather fleck
Causal agent: high levels of atmospheric pollutants such as ozone.
Signs:
Symptoms: The spots usually start as small dark green water-soaked areas. Within 48 hours, the lesions change to
a brown color then to a gray or white and appear as sunken necrotic areas bordered by chlorotic tissue (on dark
tobacco you usually do not see any yellow halo). The spots are often concentrated along the side of the midrib and
large secondary veins but can be found anywhere on the leaf. On expanding leaves the spots appear near the tip.
Lower leaf surfaces may show no evidence of damage in the early stages. Lesions may run together causing the leaf
surface to become necrotic and fall out. Symptoms may occur at any growth stage, but most commonly occur
during periods of rapid growth. Older leaves are more susceptible.
Dark fired types usually show less injury than burley types when at the same growth stage and exposed to the same
level of ozone.
The 1st row is of dark tobacco variety unknown.
The 2nd row is of dark tobacco variety ‘KT D4 LC’ which seems to be more susceptible than other dark varieties.
Note "ring spot" on the leaves. This “ring spot” (also known as "star and crescent spot") which has the form of a
necrotic spot encircled by alternating rings of healthy and injured tissue, with the necrotic rings being partial rings or
broken lines, is described in an Agronomy Journal of 1971 as physiological in cause (not being caused by a
pathogen, air pollutant, nutrient, or chemical). The book "Diseases of Tobacco" 3rd edition, puts this "ring spot" and
the reference that says it is not caused by an air pollutant, under the category of weather flecking.
We have sent similar samples in the past to a private laboratory for a tobacco virus screen and they have always
come back with negative results.
The 3rd row of images is of a dark tobacco leaf on the left and a burley tobacco leaf on the right in the field.
Total image number: 10

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: Frenching
Causal agent: metabolite of Bacillus cereus (bacterium)
Signs:
Symptoms: The image on the left is burley. The image in the middle shows an affected burley plant on the left and
an affected dark plant on the right. The image on the right shows the dark plant from the middle image, a little closer.
Total image number: 3

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: herbicide injury
Causal agent: 'picloram'
Signs:
Symptoms: Tobacco is extremely sensitive to `picloram' and small amounts from drift, contaminated equipment,
or residue in the soil will cause serious injury. Symptoms appear first on young growing leaves, but due to the
persistence of the compound, it will continue to affect the new bud leaves. `Picloram' residues may persist in the soil
and cause damage to tobacco for periods of three or more years after application.
In this case there is a question of possible contamination of the well water used to fill the floatbeds.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: herbicide injury
Causal agent: 'sulfentrazone' ("Spartan")
Signs:
Symptoms: The leaves show two primary symptoms:
1- areas or blotches of necrotic tissue that is due to splashing of “Spartan” up onto the leaf. It is associated with high
rates of the herbicide (or overlapping), wet prone soils, and/or a heavy rain preceding the onset of symptoms by a
few days. The "Spartan" label reads, under the heading "precautions": splashing of treated soil onto tobacco leaves
may cause some localized burning. Use sound transplanting practices that insure treated soil will not wash or crust
over tobacco plants."
2- a death (whitening) of the finer veins and a little puckering. This can be associated with the herbicide "Spartan"
when taken up through the roots. The injury is associated with movement of the herbicide into the root zone due to
incorporation and/or a heavy rain preceding the onset of symptoms by a few days. These symptoms are usually seen
on the older leaves and little or no symptoms on the younger ones. The plants will usually grow out of the injury
sustained earlier in the season. Plants taking up enough herbicide to cause injury later in the season will be stunted
and the leaves that are injured are not marketable.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: herbicide injury
Causal agent: acetamide herbicide containing 'alachlor’, ‘metolachlor’, ‘acetochlor’, or‘dimethenamid’.
Signs:
Symptoms: The main symptom is the producion of heart-shaped leaves. In this case we believed this was a sprayer contamination issue. The injury was diagnosed by symptomatology alone.
Total image number: 4

Plant: Tobacco (Nicotiana tabacum) Back to List
Disease/Disorder: fungicide injury
Causal agent: 'azoxystrobin' ("Quadris")
Signs:
Symptoms: Burley tobacco leaves with large spots with a water-soaked margin seen more clearly
on the bottom side of the leaves.
Image on the left is the top side of the leaves; Image on the right is the bottom side of leaves.
Total image number: 2