Ppt on Major Diseases Of Okra: Symptoms, Causal Agents And Management Strategies

This presentation covers major diseases of okra, focusing on their cause, etiology, symptoms, disease cycle, and management. Key diseases include Powdery Mildew, Fusarium Wilt, Alternaria Leaf Spot, and Yellow Vein Mosaic. Understanding the pathogens, epidemiology, and integrated management strategies is essential for effective disease control and sustainable okra production.
Introduction to Okra Diseases
  • Okra (Abelmoschus esculentus) is affected by several fungal and viral diseases.
  • Major diseases: Powdery mildew, Fusarium wilt, Alternaria leaf spot, Yellow vein mosaic.
  • Effective management requires knowledge of pathogens, symptoms, and control measures.
Powdery Mildew – Pathogen, Symptoms, Disease Cycle, Management
Pathogen: Erysiphe cichoracearum
Symptoms:
  • White or grayish powdery growth on upper leaf surfaces, later covering entire leaf.
  • Lower leaf surfaces may also be infected.
  • Affected leaves dry and fall prematurely, reducing yield.
Disease Cycle:
  • Overwinters as dormant mycelium or cleistothecia on infected leaves.
  • Secondary spread by wind-borne conidia.
  • Favored by 60–80% relative humidity and dry conditions.
Management:
  • Spray fungicides: wettable sulphur (0.25%), dinocap (0.1%), carbendazim (0.1%), hexaconazole (0.05%), or difenoconazole (0.05%).
  • Repeat sprays at 10–14 day intervals.
  • Biocontrol: Ampelomyces quisqualis, Trichoderma spp., Bacillus subtilis.
  • Use azadirachtin (0.03% EC) as needed.
Fusarium Wilt – Pathogen, Etiology, Symptoms, Disease Cycle, Management
Pathogen: Fusarium oxysporum f. sp. vasinfectum
Symptoms:
  • Yellowing, stunting, wilting, and rolling of leaves.
  • Dark brown vascular discoloration in stems.
  • Severe cases: stem blackening and plant death.
Etiology:
  • Produces hyaline mycelium, microconidia (single/two-celled), macroconidia (3–4 septa), and chlamydospores.
Disease Cycle:
  • Survives as chlamydospores in soil and infected seeds.
  • Optimum temperature for growth: 25°C; disease develops at 22–28°C.
Management:
  • Use healthy, treated seed (carbendazim 0.2%).
  • Practice crop rotation and soil solarization.
  • Remove and destroy affected plants.
  • Grow resistant varieties: CS-3232, CS-8899, IS-6653, IS-7194, Pusa Makhameli, Pusa Sawani.
Alternaria Leaf Spot – Pathogen, Etiology, Symptoms, Disease Cycle, Management
Pathogen: Alternaria alternata
Symptoms:
  • Brown leaf spots with pale margins and yellow halos.
  • Lesions enlarge, show concentric rings, and coalesce.
  • Severe infection causes leaf drying and defoliation.
Etiology:
  • Produces cylindrical conidiophores and brown, muriform conidia with transverse and longitudinal septa.
Disease Cycle:
  • Survives in infected plant debris, weed hosts, and seeds.
  • Secondary spread by wind-borne conidia.
Management:
  • Remove and destroy infected debris and weeds.
  • Seed treatment with Thiram (6 g/kg).
  • Spray Mancozeb (0.2%) after disease appearance.
Yellow Vein Mosaic – Pathogen, Symptoms, Disease Cycle, Management
Pathogen: Yellow Vein Mosaic Virus (YVMV)
Symptoms:
  • Vein yellowing and thickening, forming a network pattern.
  • Leaves become chlorotic and yellow under severe infection.
  • Plants are stunted with small, pale fruits.
Disease Cycle:
  • Transmitted by whitefly (Bemisia tabaci) in a persistent manner.
  • Wild and cultivated plants act as inoculum sources.
  • Favored by dry, hot weather with low rainfall.
Management:
  • Destroy wild hosts and avoid mixed cropping with pumpkin.
  • Adjust sowing dates to avoid peak whitefly populations.
  • Remove infected plants up to 55 days after sowing.
  • Grow resistant cultivars: Punjab Padmini, Punjab-8, Prabhani Kranti, Hissar Unnat.
  • Spray systemic insecticides (cypermethrin, deltamethrin, triazophos) to control vectors.
Summary: Integrated Disease Management in Okra
  • Use disease-free, treated seeds and resistant varieties.
  • Practice crop rotation, field sanitation, and timely removal of infected plants.
  • Apply recommended fungicides and insecticides judiciously.
  • Adopt biological control agents where feasible.
  • Monitor fields regularly for early detection and management.

Objective Questions

Q1. Which causal organism is responsible for powdery mildew in okra?
A. Erysiphe cichoracearum
B. Fusarium oxysporum f. sp. vasinfectum
C. Alternaria alternata
D. Yellow Vein Mosaic Virus
Answer: A

Q2. What is the optimum temperature range for Fusarium wilt disease development in okra?
A. 15–20°C
B. 22–28°C
C. 30–35°C
D. 10–15°C
Answer: B

Q3. Which structure allows Fusarium oxysporum to survive in soil for long periods?
A. Cleistothecia
B. Chlamydospores
C. Conidiophores
D. Sclerotia
Answer: B

Q4. Which of the following is NOT a recommended management practice for yellow vein mosaic in okra?
A. Spraying systemic insecticides
B. Mixed cropping with pumpkin
C. Removal of wild hosts
D. Use of resistant cultivars
Answer: B

Q5. Which symptom is characteristic of Alternaria leaf spot in okra?
A. White powdery growth on leaves
B. Brown spots with concentric rings
C. Vein yellowing and thickening
D. Blackening of stem
Answer: B

Q6. Which fungicide is recommended for seed treatment against Alternaria leaf spot in okra?
A. Carbendazim
B. Mancozeb
C. Thiram
D. Wettable sulphur
Answer: C

Q7. What is the main vector for transmission of yellow vein mosaic virus in okra?
A. Aphid
B. Thrips
C. White fly
D. Leafhopper
Answer: C

Q8. Which of the following is a biological control agent used against powdery mildew in okra?
A. Bacillus subtilis
B. Thiram
C. Cypermethrin
D. Deltamethrin
Answer: A

Q9. Which symptom is NOT associated with Fusarium wilt in okra?
A. Yellowing and stunting
B. Dark brown vascular discoloration
C. Brown spots with yellow halo
D. Wilting and rolling of leaves
Answer: C

Q10. Which of the following is a resistant variety for Fusarium wilt in okra?
A. Punjab Padmini
B. CS-3232
C. Prabhani Kranti
D. Hissar Unnat
Answer: B