Sclerotium disease

Sclerotium rolfsii is a very common soil-borne fungus infecting a wide range of vegetable, ornamental and field crops. It is most active during warm, wet weather in tropical and subtropical regions. The fungus causes rots of the lower stem, roots and crown. It can also cause rot of fruit in contact with the soil.

Cause

The fungus Sclerotium rolfsii.

Symptoms

Symptoms develop on plant parts in or near the soil. The most common symptom is a brown to black rot of the stem near the soil line. The stem becomes girdled and the plant wilts suddenly and dies. A coarse, white, cottony fungal growth, containing white, spherical resting bodies (sclerotia) covers the affected area. The sclerotia soon become light brown and resemble cabbage seed. Fruit symptoms usually develop where there has been contact with the soil. Decay may progress rapidly, eventually causing complete collapse.

How it spreads

The fungus can survive for years as sclerotia in the soil or in host plant debris. Sclerotia spread with soil movement, infested plant material and contaminated equipment. Infection and disease development are favoured by warm, moist conditions. Sclerotium diseases often develop on crops produced under sub-optimal growing conditions, when plant vigour and quality has been compromised by other factors.

Crops affected

Vegetable crops commonly affected include bean, beetroot, capsicum, carrot, cucurbits, sweetpotao, potato and tomato.

Control

Control of sclerotium diseases is difficult when soil and weather conditions favour the fungus. Management systems that can reduce the disease severity include the following:

• ensure plant residues have decomposed before planting
• deep ploughing soil to bury host debris and sclerotia is a useful measure
• include non-susceptible crops such as maize and small grains in rotations to reduce inoculum levels in soil
• drench transplants with the recommended fungicides.

Chemical registrations and permits

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.