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Identification and Control Methods for Southern Blight in Carnations

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[Distribution]Shanghai, Hangzhou. [Symptoms]The disease occurs at the base of the stem near the soil surface, turning brown and rotting; when the diseased stem tissue is cut open, a tea-brown or dark brown rot develops from the outside toward the center; the xylem also discolors upward, and white mycelium growing in a feathery, radiating pattern can spread to the surrounding soil surface; afterward, on the diseased area and the surrounding soil surface mycelium, sclerotia form that are initially white and later turn yellow-brown, the size of rapeseeds; after a plant is infected, it usually collapses and dies as a whole. On cutting beds, wet rot begins at the callus formation area of the cuttings and can also cause severe root

[Distribution]Shanghai, Hangzhou.

[Symptoms]The disease occurs at the base of the stem near the soil surface, turning brown and rotting; when the diseased stem tissue is cut open, a tea-brown or dark brown rot develops from the outside toward the center; the xylem also discolors upward, and white mycelium growing in a feathery, radiating pattern can spread to the surrounding soil surface; afterward, on the diseased area and the surrounding soil surface mycelium, sclerotia form that are initially white and later turn yellow-brown, the size of rapeseeds; after a plant is infected, it usually collapses and dies as a whole. On cutting beds, wet rot begins at the callus formation area of the cuttings and can also cause severe crown rot.

[Pathogen]The pathogen is a fungus, Sclerotium rolfsii. The sclerotia are superficial, 0.5-1.0 mm in diameter, smooth and glossy, shaped like rapeseeds.

[Disease Development]The pathogen has a wide host range and can harm several dozen plant species, including cacti, orchids, squirrel's tail, cineraria, chrysanthemum, snapdragon, cosmos, dahlia, iris, tulip, hyacinth, lily, and hosta. The fungus survives as mycelium or sclerotia in diseased residues, diseased plants, wild plants, and soil. Sclerotia can survive in soil for 3-4 years, but their survival period in water and wet soil is very short. High humidity favors the spread of the pathogen, and the peak period of disease occurrence is in summer.

[Control Methods]

(1) Horticultural control: Avoid continuous cropping with susceptible plants; base fertilizer applied should be thoroughly decomposed to prevent the fertilizer from carrying the pathogen; provide appropriate ventilation and avoid planting too densely.

(2) Chemical control: Disinfect the soil before planting (see Orchid Southern Blight), or use 50% Tuzet at 5 grams per square meter. If disease occurs during the growing period, promptly dig out and remove diseased plants, disinfect the planting holes with lime, or drench with 65% zineb at 600-800 times dilution; other fungicides may also be drenched. A 20% emulsifiable concentrate at 1000 times dilution can also be used for spraying or drenching to control carnation southern blight.

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