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Rhizoctonia Aerial Blight

Fungus

Rhizoctonia solani


In a Nutshell

  • Yellowing of leaves.
  • Development of brown irregular lesions.
  • Girdling and complete death of the top of plants.
  • Defoliation.

Symptoms

Initially, circular or irregular green water-soaked spots with reddish-brown margins appear on older leaves, sometimes on separate leaflets. At later stages of the disease, lesions turn brownish or tan, and the spots start to appear on petioles, stems and young pods. Brown protrusions grow on stems and petioles. Agglutinations of leaves with cottony fungal growth are also common. Severe infections cause leaf and pod blight and defoliation. The infection is more common during late vegetative stage.

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Hosts

Trigger

The fungus Rhizoctonia solani survives in the soil or on plant debris. It can overwinter in alternative hosts such as weeds. During prolonged periods of warm temperatures (25 to 32°C) and high relative humidity, the fungi spread extensively on plants due to wind and rain. They weave leaves together and form localized mats of “webbed” foliage, giving the plant a characteristic aspect.

Organic Control

Biological agents, plant extracts and essential oils can help to control the infection. The parasitic fungus Trichoderma harzianum competes with Rhizoctonia Aerial Blight. Plant extracts of onion, garlic and turmeric reduce the growth of the fungus, in this order of efficiency. Essential oils of mentha, citronella, peppermint, palmarosa and geranium can contain the infection.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. If fungicides are needed, spray products containing fluxapyroxad in combination with pyraclostrobin. Apply fungicides no more often than twice a season. Do not start the treatment if there are less than 21 days to harvest.

Preventive Measures

  • Plant tolerant varieties.
  • Prepare seedbed and fields carefully in order not to spread the pathogen.
  • Leave sufficient space between plants to ensure good ventilation.
  • Crop rotation with non-host crops (corn and sorghum) for at least 2 years is recommended.
  • Avoid excessive weed growth (weed can serve as an alternative host).
  • Plow deep to rid the soil from any remaining pathogen.

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