WELCOME

Potato and Tomato Diseases

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

Fungal diseases

Early blight Alternaria solaniLate 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

black scurfRhizoctonia solani

Wart Synchytrium endobioticum

Bacterial wilt = brown rot Ralstonia solanacearumBlackleg and bacterial soft rot  Erwinia carotovora subsp. atroseptica

Ring rot Clavibacter michiganensis 

Common scabStreptomyces scabies S. turgidiscabies

Bacterial Disease  

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

Viral

Nemic

Potato cyst nematode Globodera rostochiensisGlobodera pallida

Lesion nematode Pratylenchus spp.

Root knot nematode Meloidogyne incognita,M. javanica,

Aerial tubers

Phytoplasma infection or anything that constricts the stem, including but not limited to Rhizoctonia canker,

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 necrosis

Oxygen deficiency of tuber accompanying high soil temperature

Stem-end browning Exact cause(s) unknown, chemical injury, viruses or other pathogens.

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.

• 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

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

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

 

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).

• 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.

• 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.

Fusarium wilt

• 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

Common ScabStreptomyces 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.

Brijal Diseases

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.

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

• 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.

Phomopsis Blight Phomopsis vexans

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%

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.

• 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&94. 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.

Little LeafTransmission- 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

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.

MOSAICCharacteristic 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.

TransmissionContact &aphids

Control 1.Rogue out the affected plants.2.Collect the seeds from virus free plants.3.Avoid unnecessary touching of plants.4.Use virus free seedlings

Spray with Malathion 50 EC @0.1% at 15 Days interval

Control :1.Obtain seeds from healthy fruits.2.Treat the seed with 2g of Thiram per kg of seed before sowing.3.Spray the crop with 750g of Indofil M-45 Blitox 50 WP 250 litres of water/acre at10 day interval. Give first-spray in the 1stweek of July followed by 3-4 moresprays.

                                                                                                                                                  

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

• Leaf spot can be controlled by spraying Mancozeb 2 g/lit or Copper oxychloride 2.5 g/lit.    

Cercospora leafspot in chilli

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.

CucurbitPowdery Mildew Erysiphe cichoracearumAppear 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.

Downy Mildew Pseudoperonospora cubensis Angular, chlorotic lesions on the foliage.  Lesions appear angular because they are bound by leaf veins. 

In humid conditions, inspection of the underside of the leaf reveals gray-brown to purplish-black ‘down’. 

This is the sporulation of the pathogen. Eventually, leaves will turn necrotic and curl upwards.  The disease is sometimes called “wildfire” because of how rapidly it progresses, as if burned by fire. 

Control1.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

irrigation, 6. Apply contact fungicides

chlorothalonil /maneb or systemic

cymoxanil/famoxadone, dimethomorph

cymoxanil, Pamocarb

Fig. When moisture and temperature are conducive, downy

mildew will quickly spread within a field and to other fields. Leaf

lesions will become numerous, coalesce, and turn brown. Leaf edgesmay turn up, making the plants appear

scorched.

Mosaic

Okra

Spray 1 per cent Bordeaux mixture or copper oxychloride 3 g/1 at 15 days interval.

Disease: Leaf spot of betel vineCausal organism: Colletotrichum piperisSymptoms•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.

Disease: Leaf rot of betel vineCausal organism: Phytophthora parasitica var. piperinaSymptoms•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.

Disease: Frog eye leaf spot of tobaccoCausal organism: Cercospora nicotianae SymptomsNumerous, 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.

Disease: Brown spot of tobaccoCausal organism: Alternaria longipes/A. tenuisSymptomsThe 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.

Thanks to allThanks to all

K. M. Golam DastogeerLecturerDepartment of Plant PathologyBangladesh Agricultural universityMmensingh-2202