Disease on vegetables

Club root of crucifers- Plasmodiophora brassicae

Symptoms

• Club like swelling of roots and rootlets due to hypertrophy or hyperplasia.
• Stunting and yellowing of plants and wilt on hot days.
• It is prevalent on acidic soils (pH- <7) and less serious on heavy soils

Mode of spread or survival

It is soil borne fungus . It survives in the crop residues in the form of minute resting spores for at least 10 years. Contaminated soil can be caused by carts, tools and on the feet of human being.

Management

• Soil fumigation with methyl bromide 1kg/10m2 followed by covering with plastic film.
• Seed treatment with Captan/Thiram 4g/kg, followed by Trichoderma viride.
• Application of lime 2.5 t/ha to bring pH above 7.
• Soil drenching with copper oxychloride 0.25%.
• Discard transplanting of seedlings if clubroot is found on any seedling as it infests the main field.

Alternaria leaf spot- Alternaria spp.

Symptoms

• The pathogen affects leaves, stem, pods and seeds.
• The symptoms first appears as pin-sized black specks. The specks enlarge concentrically creating a distinct target spot or bull’s eye lesion with a yellow halo.
• Symptoms are typically seen on older and lower leaves first.
• Black sooty spores are produced on the surface during extended periods of high humidity.
• Lesions are visible from both sides of the leaf and necrotic lesions can easily tear.

Management

• Use clean and treated seeds.
• Remove or bury plant debris
• Rotate crops and perform a 3 year rotation of brassica crops.
• Use fungicides like Mancozeb @ 0.25% and spray with the initiation of specks.

Damping off- Pythium aphanidermatum/ Rhizoctonia solani

Symptoms

• Seedlings fail to emerge from the soil.
• Cotyledons and seedling stems are water soaked, soft, mushy and may be discolored gray to brown.
• Seedling stems become water soaked and thin, almost thread like, where infected. Seedlings topple down.

Mode of spread – pots, tools and potting media that have been used in previous seasons are not properly cleaned can harbor the pathogens. Infected plant debris.

Management

• Sterilize all the used pots and trays in a solution of 10% household bleach by soaking for 30 minutes.
• Used raised seed beds and avoid water logging in nursery beds or main field with better drainage.
• Drench field with copper oxychloride @0.2 % .
• Seed treatment with thiram @3g/kg of seed or with Trichoderma viridae @4g/kg of seed.
• Spray metalaxyl @0.2% when the weather is cloudy.

Late blight of potato- Phytopthora infestans

Symptoms

• Leaves, stems and tubers are affected by the pathogen.
• Water soaked spots appear on leaves, increase in size, turn purple brown and finally black in color.
• White mycelium grows on the underside surface of the leaves. This spreads to petioles, rachis and stem.
• On tubers, purplish brown spots spread to the entire surface. On cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.

Factors responsible for disease development

• Relative humidity= >90%, day temperature- 10-25 C, Night temperature- 10C. Cloudiness on the next day with intermittent rainfall.
• Soil and infected tuber serves as the primary source of infection
• Air borne infections is caused by the sporangia.

Management

1)Protective spraying with fungicides like mancozeb @0.2% should be done to prevent infection of tubers with the early spots of infection seen on leaves.

2) Haulm pulling or destruction of foliage few days before harvest is better to stop infection spread to tubers.

3) Use of resistant varieties like CIP 393077.159, LBr40

Early Blight of Potato- Alternaria solani

Symptoms

• Brown- black necrotic spot-angular, oval shape characterized by concentric rings.
• Several spot coalesce and spread all over the leaf. Shot holes on fruits.

Factors affecting disease development

Temperature- 25-30 C, dry warm weather with intermittent rain. Poor vigor and poorly manured crop.

Conidia are club shaped with a long beak with half the long of the whole conidium. There may be 5-10 transverse septa and there may or maynot be few longitudinal septa.

Primary spread- conidia on over-wintered mycelium

secondary spread- with wind, rain and insects

Management

• Disease free seed tubers should be used for planting.
• Removal and destruction of infected plant debris should be done as spores lying in the soil are the primary source of infections.
• Early spraying of captan or mancozeb @ 0.2% and repeat at 15-20 days interval for effective control.
• Planting of disease resistant variety.

Fusarium wilt- Fusarium oxysporum

Symptoms

• It is characterized by wilting of the plant and upward and inward rolling of the leaves. The leaves turn yellow and die.
• Initial slight yellowing of the foliage and wilting of the upper leaves. In later days, permanent wilting of leaves still attached is observed.
• The vascular system of the plant is discolored particularly on the lower stem and roots.

Management

1)Use of wilt resistant varieties.

2) Drenching with 1 % Bordeaux mixture to give protection.

3) Seed treatment with 4 g Trichoderma formulation or 2 g Carbendazim per kg seed is effective.

4) Mix 2 kg Trichoderma formulation with 50 Kg FYM, sprinkle water and cover with thin polythene sheet. When the mycelial growth is seen on the heap after 15 days, apply the mixture in rows of plantation.

Bacterial wilt- Erwinia tracheiphila / Pseudomonas solanacearum

Symptoms

1) Symptoms first appear on a single leaf which suddenly wilts and becomes dull green.

2) The bacteria spreads through the xylem vessels of the infected runner to the main stem, then to other runners and whole plant shrivels and dies.

3) White bacterial ooze is released from the xylem vascular bundles of affected stem if it is cut crosswise near the ground and squeezed.

Management

• Beetles are the major cause of the disease spread. So, plants should be protected from insect infestation like carbaryl, malathion, at weekly interval.
• Spray of streptomycin can be done to prevent infection spread.

Bacterial soft rot- Erwinia carotovora

Symptoms

• Fleshy fruit peduncle is highly susceptible and is frequently the initial point of infection.
• On both ripe and green fruits, the lesions are light to dark-colored, water-soaked, and some what sunken.
• The affected areas expand rapidly under high temperature and tissues lose their texture.
• In later stage, bacterial ooze may develop in affected areas. The affected fruit hang from the plant like water-filled bag. In post-harvest stage, softening of stem end of fruit is observed.

Management

• Use of antibiotics like streptomycin should be done in field condition.
• Use chlorinated wash water to reduce population of bacteria and infection risk while washing. Allow fruit to dry thoroughly.
• During packaging and storage, the fruit should be kept clean in cool and dry place.

Cercospora leaf spot- Cercospora solani

Symptoms

1) The leaf spots are characterized by chlorotic lesions, angular to irregular in shape, later turn grayish brown.

2) Profuse sporulation is seen at the centre of the spot.

3) Severely infected leaves drop off prematurely, resulting in reduced fruit yield.

4) Air borne conidia is the source of spread.

Management

• Use of resistant variety of crop
• Spray 1% Bordeaux mixture or 2 g copper oxychloride or mancozeb 2.5g/lt of water effectively to control leaf spots.

Writer: RAJARAM YADAV