Causes and Favourable Conditions

Powdery mildew spreads rapidly under the following conditions:

• Warm temperatures of 20–30°C during the day.
• High humidity levels (above 80%) & cool temperatures at night.
• Poor air circulation in the crop.
• Dense plant canopies.
• Overuse of nitrogen fertilizers.
• Infected plant debris and weeds acting as hosts.

Symptoms of Powdery Mildew

• Initially, white powdery spots appear on the lower surface of older leaves.
• Further, infection spreads to upper surface of the leaves, covering the entire leaves, stems, and sometimes fruit surfaces.
• As the disease progresses, infected leaves exhibit curling along with interveinal yellowing, which eventually lead to drying of leaves.
• Affected plants show poor photosynthesis with defoliation & stunted growth, which further reduces fruit quality and fruit setting, impacting overall yield.
• Powdery mildew can also cause cracking or deformities in fruit, making them unmarketable.

Life cycle of Powdery mildew

1. Overwintering (Survival Stage)

• Leveillula taurica, the fungus causing powdery mildew survives in unfavourable conditions (e.g. dry or cold weather) by overwintering primarily as chasmothecia (fruiting bodies containing spores) in crop residues above the soil surface.
• These overwintering chasmothecia, are resistant structures containing overwintering spores (ascospores)

2. Dispersal

• Under the favourable condition, the overwintering spores (ascospores) are released and carried by wind, insects, or water splashes to nearby healthy plants.

3. Germination and Infection

• Ascospores land on the leaves, especially on the lower surface of the leaves and germinates which further penetrates the leaf through stomata causing primary infection.

4. Colonization

• L. taurica penetrates the leaf through stomata and develops within the leaf tissue and forms a mycelial network and produces more conidia on the leaf surface.
• Fungal colonization is favoured by high day temperature and low night temperature with high humidity.

5. Reproduction and Re-spread

• The fungus produces asexual conidia which act as secondary source of infection, repeating the cycle throughout the growing season.
• Multiple infection cycles can occur (polycyclic disease), especially in warm, humid conditions.

Management and Control Measures

1. Cultural Practices

• Maintain adequate plant spacing to improve air circulation.
• Remove severely infected leaves through pruning and destroy them to prevent further spread.
• Avoid solanaceous crop rotation with in the same area continuously to prevent disease build-up.
• Removal of weeds & plant debris that may harbour fungal spores to reduce the risk of infection.
• Avoid excessive nitrogen use in fertilization, as it promotes dense foliage, creating favourable conditions for mildew.
• Use drip irrigation instead of overhead watering to reduce humidity around plants and avoid the spread of fungal spores.
• Apply organic mulch to regulate soil moisture and temperature while reducing spore dispersal.
• Use varieties that exhibit resistance to powdery mildew, as breeding programs have identified resistant lines that can significantly reduce disease incidence.
• Regularly clean and disinfect tools, greenhouse structures, and equipment to prevent the spread of fungal spores.

2. Biological and Organic Control

• Multiplex Mahan – 10kg/acre or Multiplex Neempure P – 8kg/acre has to be incorporated into the fields before sowing.
• Multiplex Rognash B at 2-3ml/L can be applied to the crop in the initial stages. Prior to spraying the entire crop, test a small portion of the crop for sensitivity.
• As a prophylactic measure, mix 2 to 5 kg of Multiplex Nisarga or Multiplex Bio Jodi along with 120-150 kg of Multiplex Annapurna and broadcast over one acre before planting.

3. Chemical Control

• The chemical spray should be taken by altering the different recommended molecules belonging to different modes of action in a rotational basis to prevent the development of resistance.
• For foliar application use fungicides like Nagcarzim @ 1.5 – 2g/L or Vishesh @ 2g/L or Sergent @ 2ml/l or Nagzol @2ml/L or Tecozo @ 1- 2 ml or Nagsulp SC @ 3ml/L or Tough @ 2g/L or Nagcoper @ 2- 3g/L.
• Combi products like Duo Care @ 1-1.5 ml/L or Ziddhi @ 2g/L or Jodi @ 2g/L or Tecsulp @ 2g/L are also effective in controlling powdery mildew disease.

• Triazole fungicides like Propiconazole, Tebuconazole, Difenoconazole, Hexaconazole etc. are generally very effective against powdery mildew.
• Initiate fungicide applications at the first sign of disease and continue at recommended intervals, as early intervention is crucial for effective management.