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.
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.
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.
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.