Tobacco Disease, Frog Eye Leaf spot, Mosaic of Tobacco, Leaf Curl with Symptoms Favourable condition Control Measure
Tobacco Disease
Frog Eye Leaf spot
Causal organism: Cercospora nicotianae.
Symptoms
1.
Small roundish spot are developed on the leaves, especially on the older
leaves.
2.
The spots enlarge and become roughly circular in shaped.
3.
The centre of the spots turns white or pale brown surrounded by a dark black
margin resembling the eye of a frog.
4.
More than one lesion coalesce together to form a bigger lesions and maximum
portion of leaves dry down and finally fallen it.
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| Frog Eye Leaf spot. https://cststudy.blogspot.com/ |
The
fungus may over winter in the crop residues, plant debris and on the collateral
host. From this source, the air borne conidia because primary infection
then favourable condition, it may cause secondary infection.
Favourable condition
•
Close plantation.
•
Frequent irrigation/rainfall.
•
High Relative humidity, above 80%.
•
Excess use of nitrogenous fertilizer.
•
Windy weather.
•
Insect infestation.
•
Present of wounds.
Control Measure
A. Cultural method
Cultural
method is good for minimizing the disease;
v Optimum
fertilizer management.
v Optimum
irrigation as a when necessary.
v Weeding
of collateral host.
v Sanitation
of the field.
B. Chemical method
v Spraying
Bordeaux mixture usually 2 times at 10-12 days interval.
v Spraying
of fungicides like Macuprax, Cupravit, Dithane M45 @ 2% solution at
2-3 times onset of disease at 20 days interval.
Mosaic of Tobacco
Causal organism: Tobacco Mosaic Virus
(TMV).
Origin
Adlof
Mayer at first reported this disease in 1886. In 1892 Iwanowski demonstrated
that tobacco mosaic virus would pass through a bacteriaproof filter. It
is the first reported viral disease in the world. Has long association
with other viral diseases.
Symptoms
1.
Discolored vein/Yellowing of the vein of leaf.
2.
Green patches and yellow patches are alternate with each other. This is the
most characteristics symptom of leaf mosaic of tobacco.
3.
Three type of characters such as mottling, Distortation and Stunting are seen
on the leaves.
4.
Infected bud leaves become twisted and malformed.
5.
If infection make earlier, severe dwarfing of plant reduced yield and reduction
yield quality.
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Mosaic of Tobacco. https://cststudy.blogspot.com |
Favourable condition
•
Excess use of nitrogenous fertilizer.
•
Windy weather.
•
Insect infestation.
•
Present of wounds. Intensity of disease Intensity of
disease depend on physical and environmental condition. The virus can survive
in dried tobacco leaves upto 5 years and infected plant juice upto 25
years.
Transmission
TMV
transmitted by sap. It is done mechanically (Animal, knife, labour hands etc).
Control Measure
v Field
sanitation.
v Highly
contagious disease; washed the used implements as well as labour hands by
running
water.
v Roughing
and cultural practices.
v Seed
bed soil should be sterilized by steam.
v Destruction
of collateral host.
v Balanced
fertilizer are used (optimum Nitrogenous fertilizer).
v No
chemical is recommend for TMV.
Leaf
Curl
Causal organism: Tobacco leaf curl
virus.
Symptoms
1.
There is no change in the colour of the infected leaves.
2.
Size of the leaves are usually smaller.
3.
Downward turning of the infected leaf, exposed in the mid rib. The mid rib
exposed upward giving an inverted boat shaped.
4.
Leaf blade will be thicker.
5.
Young apical leaves become twisted.
6.
Plant become dwarf and inflorescence remain condensed.
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| Leaf Curl of tobacco. https://cststudy.blogspot.com |
Favourable condition
•
Excess use of nitrogenous fertilizer.
•
Windy weather.
•
Insect infestation.
•
Present of wounds.
Transmission Cycle: Same as tobacco
mosaic disease.
Control Measure
v Remove
and destroy the infected plants.
v Rogue
out the reservoir weed hosts which harbour the virus and whiteflies. Planting tobacco
crop during the crop periods when the vector population is low.
v Field
sanitation.
v Highly
contagious disease; washed the used implements as well as labour hands by
running water.
v Balanced
fertilizer are used (optimum Nitrogenous fertilizer).
v Spraying
Sevin 85 WP @ 1.7 kg/ha for control white fly.
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