This document provides information on diseases that affect tomatoes, including early blight, late blight, and other bacterial and viral diseases. Early blight is caused by Alternaria solani and presents as dark brown spots on leaves and stems. Late blight is caused by Phytophthora infestans and results in large, dark brown leaf blotches and spots on fruits and stems. Management of these diseases involves cultural controls like removing debris, improving airflow, and rotating crops, as well as applying fungicides in a preventative manner.
6. Early blight - Alternaria
solani
• Early blight is the most destructive disease of
tomatoes in the tropical and subtropical regions.
Each 1% increase in intensity can reduce yield by
1.36%, and complete crop failure can occur when the
disease is most severe.Yield losses of up to 79%
have been reported in the U.S., of which 20-40% is
due to seedling losses (i.e., collar rot) in the field.
• It can affect almost all parts of the tomato plants,
including the leaves, stems, and fruits.
• The plants may not die, but they will be weakened
and will set fewer tomatoes than normal.
7. Leaves
Initially small dark spots form on older foliage near the
ground
Leaf spots are round, brown and can grow up to half inch
in diameter.
Larger spots have target board or bull eye symptom
like concentric rings and tissue around spots often turns
yellow.
Severely infected leaves turn brown and fall off, or dead,
dried leaves may cling to the stem
Stem
Seedling stems are infected at or just above the soil line.
The stem turns brown, sunken and dry (collar rot). If the
infection girdles the stem, the seedling wilts and dies.
Stem infections on older plants are oval to irregular, dry
brown areas with dark brown concentric rings.
Fruit
Fruit can be infected at any stage of maturity
Fruit spots are leathery, black, with raised concentric
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15. FAVOURABLE CONDITION :
Disease develops at moderate to warm 15 to 27
degree celsius;
Rainy weather or heavy dew, 90% humidity ,
June-July sowing - weak and old plants prone to
infection high soil moisture.
DISEASE CYCLE :
PSI : Mycelium or conidia in infected plant debris.
SSI : Conidia by wind, water or rain splash .
Mode of spread:
Seed borne and air borne conidia
16. spore
Light brown conidia with muriform
shape, but the isolates varied in the size
(length, width and beak length) of the
conidia, the number of cells per
conidium and sporulation times.
Among the nitrogen sources, potassium
nitrate followed by sodium nitrate and
ammonium molybdate increased the
growth of mycelium.
Low pH (4-4.5) was found as ideal for
the growth of A. alternata, while the
minimum growth was observed in pH
9.0, irrespective of isolates
The conidia of A. alternata isolates
germinated at 46°C.
18. MANAGAMENT
CULTURAL CONTROL
Use pathogen-free seed, or collect seed only from
disease-free plants.
Remove infected debris from field to reduce inoculum
for the next year.
Water plants in the morning so plants are wet for the
shortest amount of time.
Apply plastic or organic mulch to reduce humidity and
provide a barrier between contaminated soil and leaves.
Use a drip irrigation than over head system to minimize
leaf wetness which provides optimal conditions for
fungal growth.
Rotate to a non-Solanaceous crop for at least three
years.
If possible control wild population of Solanaceae. This
19. IIHR 2101 (Solanum habrochaires LA-1777) showed highly
resistant reaction, IIHR- 2758 showed moderately resistant
reaction
Fertilize properly to maintain vigorous plant growth.
Particularly, do not over-fertilize with potassium and maintain
adequate levels of both nitrogen and phosphorus.
For greenhouse production, early blight has been reduced by
as much as 50% by covering houses with UV-absorbing vinyl
film.
Increase air circulation in rows. Damp conditions allow for
optimal growth of A. Solani and the disease spreads more
rapidly. This can be achieved by planting farther apart or by
trimming leaves.
CHEMICAL CONTROL
Some of the fungicides are chlorothalonil, copper
product,mancozeb, potassium bicarbonate, and ziram.
Bacillus subtilis
FORECAST MODEL EPIDEM
20. LATE BLIGHT- Phytophthora infestens
Late blight is a potentially devastating disease of
tomato and potato, infecting leaves, stems, and fruits
of tomato plants. The disease spreads quickly in
fields and can result in total crop failure if untreated.
Late blight of potato was responsible for the Irish
potato famine of the late 1840s.
phytophthora in Latin means "plant destroyer."
Infected plant tissue dies.
21. Signs and symptoms :
Leaves :
Leaves have large, dark brown blotches with a
green gray edge; not confined by major leaf veins
Infections progress through leaflets and petioles,
resulting in large sections of dry brown foliage.
Stem :
Stem infections are firm and dark brown with a
rounded edge.
Fruit :
Firm, dark brown, circular spots grow to cover large
parts of fruits. Spots may become mushy as
secondary bacteria invade.
In high humidity, thin powdery white fungal growth
appears on infected leaves, fruit, and stems
In cool, wet weather, entire fields turn brown and
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31. FAVOURABLE CONDITIONS:
High relative humidity >90 %
Low temperature 10 – 25 degree celsius
Cloudy weather and rainfall with splashing rains.
DISEASE CYCLE :
PSI : Oospores in the infected debris and soil.
SSI : Sporangia or zoospores dispersed by wind
or
rainwater
Mode of spread:
Soil borne-spread through sporangia or zoospores
dispersed by
wind or rainwater.
32. MANGEMENT :
CULTURAL METHOD
Destroy potato piles before the growing season
begins,
Control volunteer potato plants, as infected plants
can grow from infected tubers.
Seed infection is unlikely on commercially prepared
tomato seed or on saved seed that has been
thoroughly dried.
If infection is found in only a few plants within a field,
infected plants should be removed, disced-under,
killed with herbicide to avoid spreading through the
entire field
Movement of water from infected to healthy field
should be avoided.
Crop rotation with cereals
33. CHEMICAL CONTROL
Prophylactic sprays with copper fungicides or
dithiocarbomates 0.25% .
Metalxyl / amiston 0.2%.
FORECAST MODEL : TOMCAST
