Symptom Identification and Control Methods for Southern Blight in Impatiens

Southern blight in impatiens attacks the roots, stems and fruits of plants, causing damping-off, root rot, basal rot and fruit rot. This disease can also harm plants such as iris, orchids, peonies, peaches and plums.

Symptoms: In the early stage of the disease, a brownish-black wet rot appears at the base of infected plants, later followed by white silky mycelium and the formation of sclerotia the size of rapeseeds. In the late stage of the disease, severely infected plants collapse with damping-off.

Pathogen: The pathogen is Sclerotium rolfsii Sacc., belonging to the Deuteromycotina, Hyphomycetes, Agonomycetales fungi.

Disease pattern: The pathogen can survive for many years in soil and plant debris as mycelium and sclerotia, and the mycelium infects plants from the root and stem base.

Control: (1) Pull out diseased plants and collect and destroy the sclerotia in the soil. Spread lime in the diseased planting holes, or use 70% quintozene powder mixed with fresh soil to make medicated soil (1:100) for soil disinfection. (2) In the early stage of the disease, drench the stem base of diseased plants with a 500-800 times dilution of 50% carbendazim wettable powder, or a 500 times dilution of 50% thiophanate-methyl wettable powder, once every 7-10 days, for a total of 2-3 times.