Diseases of vegetable crops in Bangladesh A lecture for L-4,S-1 students-Bangladesh Agricultural University by K. M. Golam Dastogeer

1. WELCOME

2. Potato and Tomato
Diseases

3. At the end of the lesson the
students will be able --
to tell list important diseases of
potato and tomato with their cause
to identify the disease by observing
the symptom
to draw life cycle of most important
diseases
To formulate the control strategy
for these diseases

4. Fungal diseases
Early blight Alternaria solani
Late blight Phytophthora infestans
Fusarium wilt Fusarium oxysporum
Verticillium wilt Verticillium albo-atrum
Fusarium dry rot Fusarium spp
Gangrene Phoma exigua f. sp. foveata
Powdery scab Spongospora subterranea f.sp. subterranea
Rhizoctonia canker and
Rhizoctonia solani
black scurf
Wart Synchytrium endobioticum

5. Bacterial Disease
Bacterial wilt = brown rot Ralstonia solanacearum
Blackleg and bacterial soft rot Erwinia carotovora subsp. atroseptica
Ring rot Clavibacter michiganensis
Streptomyces scabies
Common scab
S. turgidiscabies
Viral
Potato leafroll Potato leafroll virus
Potato mop-top Potato mop-top virus
Potato rugose mosaic Potato virus Y
Potato spindle tuber Potato spindle tuber viroid
Potato yellow dwarf Potato yellow dwarf virus
Potato yellow mosaic Potato yellow mosaic virus
Potato yellow vein Potato yellow vein virus
Potato virus X Potato virus X
Potato virus Y Potato virus Y

6. Nemic
Globodera rostochiensis
Potato cyst nematode
Globodera pallida
Lesion nematode Pratylenchus spp.
Root knot nematode Meloidogyne incognita,M. javanica,
Phytoplasma infection or anything that constricts the
stem, including but not limited to Rhizoctonia canker,
Aerial tubers
heat necrosis, chemical injury, mechanical injury,
wind injury
Air pollution injury Photochemical oxidants (primarily ozone), sulfur oxides
Black heart Oxygen deficiency of internal tuber tissue
Hollow heart Excessively rapid tuber enlargement
Internal brown spot = heat Oxygen deficiency of tuber accompanying high soil
necrosis temperature
Exact cause(s) unknown, chemical injury, viruses or other
Stem-end browning
pathogens.

7. Late blight of potato
• Great Irish Famine of 1845 to 1847
Disease symptoms and signs
• necrotic spots, may or may not
be surrounded by a pale green
border
• Older lesions generally have a
necrotic center and a chlorotic
halo
• they coalesce, blighting and
killing the entire leaf within a
few days.

8. • a white fluffy growth appears at
the lesion edges on the underside
sporulating, producing sporangia
• Irregular, slightly depressed
areas of brown to purplish skin
• A coppery brown granular rot
usually extends less than one-
half inch into the tuber

9. Fig. 3: Other seed Fig. 4.Inert matter

10. Management
• Healthy Seed-first line of defense
• Cultivar Resistance
• Removal of Diseased Plants:
• Fungicide Spraying: Fungicides – mancozeb @
0.2% or Copper oxychloride @ 0.3%. If late blight
attack is early in the season and weather conditions
are favorable, one spray of metalaxyl + mancozeb
@ 0.2% may be given

11. Early blight
• Initially on the older, lower leaves
• Lesions first appear as small spots—dry
and papery.
• Lesions become brownish black and
circular.
• Concentric rings of raised and depressed
tissue gives the lesions "target-spot" or
“bull’s eye” appearance
• Adjacent to the lesion is usually
yellowed. As new lesions develop and
older lesions expand, the entire leaf
becomes chlorotic (yellow).

12. • Tuber lesions are dark, sunken,
and circular to irregular in
shape, and often are surrounded
by a raised, purplish-gray border
Management of disease
•Use a crop rotation
•Use tillage practices such as fall plowing that bury all plant refuse.
•Select cultivars that have a lower susceptibility to early blight.
•Use certified disease-free tomato seed and transplants.
•Kill off the foliage at least 2–3 weeks before harvesting to prevent tuber infection
•Allow tubers to mature before digging.
•Avoid harvesting tubers when conditions are wet, dig when vines are dry
•Avoid excessive wounding of potatoes during harvesting and handling.
•Although the above measures are important to minimize infection, it is usually necessary to
apply fungicide sprays to fully protect plants from early blight.

14. Fusarium wilt
• develop a yellowing of the older
leaves. Often the yellowing is
restricted to one side of the plant
or even to leaflets on one side of
the petiole.
• the main stem is cut, dark,
chocolate-brown streaks may be
seen running lengthwise through
the stem
• tubers may show browning of
the vascular ring as well as
browning at the stem end

15. Common Scab
Streptomyces scabies
• Lesions typically are circular, raised, and tan to
brown in color, with corky areas that develop
randomly. Lesions may become irregular in
shape when they coalesce .
• A superficial corklike layer (russet scab)
occasionally appears instead of the circular
lesions.
• In other cases, the lesions are one-half inch
deep (pitted scab). These pitted scab lesions
are dark brown to black, and the tissues
underneath are often straw-colored and
translucent.
• More than one type of symptom may be present
on a single tuber.

16. Brijal Diseases

17. Damping off (Phytophthora, Rhizoctonia or
Pythium sp.)
1. Pre-emergence damping-off:
• Results in seed and seedling rot before these
emerge out of the soil.
• Young seedlings are killed before they reach the
surface of the soil.
• Since this happens under the soil surface, the
disease is often not detected except for the
resulting poor stand
2. Post-emergence damping-off:
• Characterized by toppling over of infected
seedlings.
• Collar portion rots and ultimately the seedlings
collapse and die.

18. Management
•Healthy seed
•Seed treatment with Thiram @ 2g/kg of seed before sowing.
•Soil treated with Thiram @ 5g/m2 area of the soil/ Formalin
•Soil drenching with the same chemical @ 2g/litre of water at fortnightly
interval.
•Soil solarization by spreading polythene sheet over the bed for 30 days
before sowing
•Application of BAU- biofungicide (T. viride) in soil @ 1.2kg/ha
•Continuous raising of nursery in the same plot should be avoided.
Additional precautions:
a) Thin sowing to avoid overcrowding.
b) Light sandy soils for nurseries or use pure fine
sand sawdust mixture for raising seedlings.
c) Use well-decomposed manure.
d) Light but frequent irrigations.
e) Raised nursery beds to drain off excess water, and
f) Sterilization of soil by burning a 30cm thick stack of
farm trash on the nursery bed before seed

19. Phomopsis Blight Phomopsis vexans
• seedling infection-------------damping off
symptoms
• leaves infected-----------small circular spots
appear which become grey to brown with
irregular blackish margins
• Lesions may also develop on petiole and
stem, causing blighting of affected portion of
the plant
• Fruits infection-------minute, sunken dull and
dusky spots which later merge to form rotten
areas. The flesh of severely infected fruits
rots
• At advance stage, numerous pycnidia as
small, black pimples embedded in the host
tissue are seen.

20. Control
•Healthy seeds
•Good field sanitation,
•Destruction of infected plant material
•crop rotation
•Disease resistant variety e.g BAU begun-1&2
•Seed treatment with hot water (51oC for 15 minutes)/
Thiram (2 g/kg seed)
•Spraying with Zineb (Dithane-Z-78) or Mancozeb (Dithane
M-45)/Bavistin @ 0.2%

21. Wilt
Bacterial Wilt (Psedomonas solancearum)
•The characteristic symptoms of the
disease are wilting of the foliage followed
by collapse of the entire plant.
•Wilting is characterized by gradual,
sometimes sudden, yellowing, withering
and drying of the entire plant or some of its
branches. Verticillium Wilt (Verticilium dahliae) :
•Infected young plants show dwarfing and stunting with no
flower and fruit.
•Infection after the flowering stage results in distorted
floral buds and fruits. Affected fruits finally drop off.
•infected leaves show irregular, scattered necrotic pale
yellow spots over the leaf lamina. Later on, these spots
coalesce resulting in complete wilting of leaves.
•Roots are split open longitudinally, a characteristic dark
brown discoloration in the xylem vessels is observed.

22. • How to Mange Bacterial wilt?
1. Clean and well drained land.
2. Grafting with resistant Solanum root stock.
3. Cultivate moderaterly tolerant variety like BARI
Begun-6,7&9
4. Dip seedlings into streptrocycline (1gm/40 L
water) for 30 minutes.
5. Other solanaceous crops to be avoided in crop
rotation.
6. The field should be cleaned as soon as the
disease is detected in the field i.e. the diseased
fruits should be plucked and burnt.
How Can You Control V. wilt?
•Crop rotation with bhendi, tomato,
potato should be avoided.
•Soil application and foliar
application with Benlate (0.1%) is
effective in reducing the wilt
disease.

23. Little Leaf
Transmission- leaf hopper Cestius phycitis
•leaves in early stages are light yellow in color
•Leaves show a reduction in size and are malformed
plant are shorter, bearing a large number of
branches, roots and leaves.
•Give the plants a bushy appearance.
•No fruit or hard and tough fruit and fails to mature
Control Measures
i. The disease affected plants should be destroyed,
ii. Spray Dimethoate
(Rogor-30 EC)/Oxydemiton methyl (Metasystox-25
EG) or Monocrotophos (Monocil)/ Malathion@ 1 ml
per litre of water to check the spread of this disease,
iii. Disease resistant variety such as Pusa purple
Cluster should be cultivated

26. Leaf Curl
•Transmission-whitefly Bemisia tabaci
•Abaxial and adaxial curling of leaves
accompanied by puckering and blistering
of interveinal areas and thickening and
swelling of veins
• Cover nursery beds with nylon net or straw to
• Protect the seedlings from viral infections.
• Raise barrier crops such as maize, sorghum,
pearl millet or snap bean around chillies in two to
three rows
• Remove infected plant as soon as they are
noticed.
• Spray metasystox or rogar at 0.1% at 10 days'
interval.
• Spraying should be stopped 15-20 days before
harvest of the crop.

27. MOSAIC
Characteristic symptoms are appearance
of dark green and yellow areas on the
leaf surface.
These may be sunken
or raised (puckering).
Sometimes the leaves
are greatly reduced in
size and filamentous
or shoe string like.
Control
1.Rogue out the affected plants.
Transmission 2.Collect the seeds from virus
Contact &aphids free plants.
3.Avoid unnecessary touching
of plants.
4.Use virus free seedlings
Spray with Malathion 50 EC @0.1% at 15 Days interval

28. ANTHRACNOSE, DIE BACK AND RIPE FRUT ROT
Die back.
•Necrosis of the tender twigs from the tip
backwards.
•Entire branch or the entire top of the plant
may wither away.
•Twigs are water soaked to brown,
becoming greyish white or straw colored in
advance stage.
•Large number of black dots called acervuli
are formed on the affected twigs.
Ripe fruit rot.
•The disease usually occur on mature fruits
as circular to elliptical sunken spots with
black margins and marked with concentric
rings .
•Badly diseased fruits turn straw colored
from normal red. On this discolored area,
numerous black dots (acervuli) are present.
The diseased fruit may drop off
prematurely

29. Cercospora leafspot in chilli
• Leaf spot can be controlled by
spraying Mancozeb 2 g/lit or
Copper oxychloride 2.5 g/lit.
Symptoms :
•Roughly circular, cherry red to dark red spots, variable in size
are formed by C. canescens.
•In case of C. cruenta black mats due to mouldy growth of the
fungus are caused.
•Defoliation occurs in both the cases. At maturity, infected pods
show black sporulation of the fungus.

30. Cucurbit
Powdery Mildew Erysiphe cichoracearum
Appear first as a pale yellow spots
The fungus soon sporulates yielding a
characteristic powdery-white appearance.
This powdery appearance can involve the
entire leaf which eventually turns yellow
then brown and dries to the point that it
crumbles when crushed.
 Use resistant varieties.
 good drainage and allow for maximum air
circulation
 Apply protectant fungicides, such as wettable
sulfur, to susceptible plants before or in the
earliest stages of disease development.
 Spray Karathane/ chlorothalonil (e.g.
Daconil 2787 10 day intervals.

31. Downy Mildew
Pseudoperonospora cubensis
 Angular, chlorotic lesions on the foliage.
Lesions appear angular because they are
bound by leaf veins.
This is the sporulation of the pathogen. Eventually,
leaves will turn necrotic and curl upwards. In humid conditions, inspection
The disease is sometimes called “wildfire” because of of the underside of the leaf
how rapidly it progresses, as if burned by fire. reveals gray-brown to purplish-
black ‘down’.

32. Control
1.Plant varieties that are resistant to downy
mildew.
2.Wide spacing between plants, choosing
planting sites with good soil and air drainage
and exposure to all-day sun,
3.Maintain ample but not excessive nitrogen
fertility,
4. Control weeds 5. Avoiding overhead Fig. When moisture and temperature
are conducive, downy
irrigation, 6. Apply contact fungicides mildew will quickly spread within a field
chlorothalonil /maneb or systemic and to other fields. Leaf
lesions will become numerous,
cymoxanil/famoxadone, dimethomorph coalesce, and turn brown. Leaf edges
may turn up, making the plants appear
cymoxanil, Pamocarb
scorched.

33. Mosaic

34. Okra

35. Disease: Leaf spot of betel vine
Causal organism: Colletotrichum piperis
Symptoms
•The round to oval shaped spots are pale
brown color at early stage and dirty black at
later stage which appear initially as water
soaked lesions on the leaves.
•These lesions enlarge irregularly towards
the center of the leaves. The mature spots
have ashy center, dork brown distinct
margin surrounded by yellow halo.
Spray 1 per cent Bordeaux
mixture or copper oxychloride 3
g/1 at 15 days interval.

36. Disease: Leaf rot of betel vine
Causal organism: Phytophthora parasitica
var. piperina
Symptoms
•The infected area of tile leaves turn brown
to dark brown and later dirty black
•Often starting from the edge or tip of the
leaves and progress towards the centre of
the leaves without a well defined margin.
•The lesions enlarge rapidly to cover a part
or whole leaf which later starts rotting.

37. Disease: Frog eye leaf spot of tobacco
Causal organism: Cercospora nicotianae
Symptoms
Numerous, small reddish spots develop on
the leaves especially on the older leaves.
The mature spots become roughly circular
in shape. The centers of the spots turn
while brown/ash colored with a grey
circular layer surrounded by dark brown
margin. The spots look like the eye of the
frog, hence the disease so called.

38. Disease: Brown spot of tobacco
Causal organism: Alternaria longipes/A.
tenuis
Symptoms
The large, circular and brown colored spots
present on the leaves which appear initially
as pin pointed to large (5-10 mm diameter)
spots. The mature spots have dark brown
concentric rings which is the most
important diagnostic character of the
disease. Several spots near the tip may
coalesce together causing death and
drying of leaves.

41. Thanks to all
K. M. Golam Dastogeer
Lecturer
Department of Plant Pathology
Bangladesh Agricultural university
Mmensingh-2202