Damping Off Management in Onion: Symptoms, Treatment, Chemical, Biological, and Organic Control

Damping off is a fungal disease that affects the seeds and seedlings of various plants, including onions. It is caused by a group of soil-borne fungi that thrive in damp conditions and attack the base of the stem, causing the seedling to wilt and die. Onion seedlings affected by damping off may exhibit stunted growth, yellowing leaves, and a mushy stem at the soil line. The disease can cause significant damage to crops and reduce yields.

Damping Off Management in Onion

What Is Damping Off in Onions?

Damping off is a fungal disease that affects the seeds and seedlings of onions.
Soil-borne fungi, including Rhizoctonia, Fusarium, and Pythium, cause it.
The disease thrives in damp conditions and attacks the base of the stem, causing the seedling to wilt and die.
Infected seedlings exhibit stunted growth, yellowing leaves, and a mushy stem at the soil line.

Onion Plant Characteristics

Onion is a biennial plant that belongs to the Allium genus.
It has a shallow root system and a bulbous stem that grows underground.
The leaves of the onion plant are long, narrow, and green, with a waxy texture.
Onions prefer well-drained soil with a pH between 6.0 to 7.5.
They require a cool and moist climate to grow successfully.

Causes/Pathogen of Damping Off in Onion

Damping off in onions is mainly caused by the Fusarium oxysporum fungus, common in most onion-growing areas.
The Pythium sp. fungus has also been reported to cause damping-off in some regions.
The disease thrives in damp soil conditions and attacks the base of the stem, causing the seedlings to wilt and die.
The disease is more prevalent in northern and eastern India during the kharif season, causing 60-75% damage to onion crops.
Overcrowding, over-watering, and poor soil drainage are contributing factors that increase the likelihood of the disease.

The Disease Cycle of Damping Off in Onion

The damping-off disease cycle in onions begins with the fungal pathogen(s) in the soil.
The pathogen(s) survive on infected crop debris and soil, the primary inoculum sources.
The fungal spores can persist in the soil for several years, so practicing proper crop rotation and soil sterilization methods is important.
The pathogen(s) infect the seeds and seedlings when they come into contact with contaminated soil or debris.
The fungus then grows on the surface of the seedlings, causing the stem to weaken and collapse, resulting in damping off.
The disease is more prevalent in damp conditions, especially during the plant’s early growth stages.

Conditions Favorable for Damping Off Spread in the Field

Damping off in onions is more prevalent during the Kharif or rainy seasons.
The disease can cause significant damage, up to 60-75% in some cases.
High soil moisture, moderate temperature, and high humidity are favorable conditions for developing and spreading the disease.
Over-watering or poor soil drainage can increase soil moisture levels and create conditions that favor fungal growth.
Crowding of seedlings can also increase humidity levels, providing a conducive environment for fungal spores to germinate and spread.
The disease is more common in areas with heavy rainfall or poor soil drainage.
Maintaining proper soil moisture levels, spacing seedlings adequately, and practicing good sanitation and hygiene can help prevent the spread of damping off in onions.

Damage Symptoms of Damping Off

Damping off in onions can result in two types of symptoms: pre-emergence damping-off and post-emergence damping-off.
Pre-emergence damping-off causes seed and seedling rot before they emerge from the soil. Affected seeds fail to germinate, and the seedlings appear stunted or fail to emerge altogether.
Post-emergence damping-off occurs when the pathogen attacks the seedlings’ collar region on the soil’s surface. The collar portion rots and the seedlings ultimately collapse and die.
Affected young plants or trees become chlorotic, wilt, and eventually topple down, appearing cut off at the base.
White or grey mold-like growth appears on dead plants or the soil surface.

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Yield Loss Due to Damping Off on Onion

Damping off disease in onions can cause significant yield losses.
Up to 60-75% of the crop can be damaged or lost in severe cases.
The disease affects the plant’s early growth stages, which can lead to stunted growth and reduced bulb size.
Reduced plant stand and uneven growth can also impact the yield and quality of the onions.

Damping Off Management in Onion by Cultural Method

Crop rotation with non-host crops is an effective method to reduce the incidence of damping off.
Soil solarization, a technique that covers moist soil with clear plastic to trap the sun’s heat, can help kill fungal spores and reduce disease incidence.
Planting in well-draining soil can help prevent the accumulation of moisture, which favors the growth of the fungus.
Seed treatment with fungicides can protect the seedlings from damping off.
Proper irrigation practices, such as avoiding over-watering and providing adequate drainage, can also help reduce the incidence of the disease.

Damping Off Management in Onion by Biological Method

Biofungicides based on fungi Trichoderma viride, Beauveria bassiana, or bacteria such as Pseudomonas fluorescens and Bacillus subtilis can be used as seed treatments or applied around the root zone at the time of planting to prevent or control pre-emergence damping off.
These bio fungicides work by colonizing the root zone, creating a protective barrier against pathogenic fungi.
In some cases, preventive treatment of seeds with copper fungicides such as copper oxychloride or Bordeaux mixture can help reduce the incidence and severity of the disease.

Damping Off Management in Onion by Chemical Method

Fungicides can be used as a preventive measure in fields with a history of damping off or poor drainage.
Seed treatments with fungicides such as metalaxyl-M can effectively control the pre-emergence form of damping off.
Foliar spray with fungicides like Captan 31.8% or metalaxyl-M 75% during cloudy weather can help control the disease.
Soil drenching with copper oxychloride or captan every two weeks from planting can help prevent the spread of the disease.
Following the recommended rates and timings of application for fungicides is important to avoid damage to the crop and the environment.

Damping Off Management in Onion by Organic Method

Organic methods can prevent and manage damping off in onion plants.
Homemade solutions based on plant extracts of Eupatorium cannabinum have been found to inhibit the growth of the damping-off fungus completely.
Maintaining proper soil drainage and avoiding over-watering can also help prevent the disease.
Crop rotation, disease-free seeds, and good sanitation practices can also reduce the incidence and severity of damping off in onion plants.

Preventive Measures for Control of Damping Off

Use seeds from healthy plants or certified sources to avoid introducing the pathogen into the field.
If available, use onion varieties that are resistant to damping off.
Use raised beds in areas with poor drainage or wet soils to improve soil aeration and drainage.
Plant seeds or seedlings with enough space between them to promote air circulation and reduce humidity levels.
Avoid planting seedlings too deep during transplanting to prevent collar rot.
Remove infected plants as soon as symptoms appear to prevent the spread of the disease.
Adopt a balanced fertilization program with split nitrogen applications to ensure healthy plant growth.
Water regularly but shallowly, and avoid overhead irrigation.
Water in the morning hours to allow the soil surface to dry before evening.

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Conclusion

Effective management of damping off disease in onions requires a combination of preventive measures and appropriate treatment options such as chemical, biological, and organic control methods. Early detection of symptoms and prompt action can help reduce yield losses and improve crop health.

Damping Off Management in Onion: Symptoms, Treatment, Chemical, Biological, and Organic Control

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