Sclerotinia blight

Sclerotinia sclerotiorum and S. minor.

Major and expanding. S. minor is the main problem in the South Burnett, while S. sclerotiorum is the main problem on the Atherton Tableland and at Coominya.

These diseases can devastate a crop in a few days, if it is continuously wet. Sclerotinia, particularly S. sclerotiorum, shows up first in wetter parts of the paddock where the bushes are larger or where it may be in the shade for longer.

Usually the first sign of sclerotinia is a wilting branch or bush. The plant will begin to show visible wilting only after it has been infected for many days. Early detection is essential.

Both types of sclerotinia produce fluffy, white, mould-like cotton wool. The size of the black resting bodies (sclerotes) formed on and in stems is different; those of S. sclerotiorum are larger than a wheat grain, while those of S. minor are smaller and similar in size to raw sugar crystals. Stems wilt and become dry and bleached where the fungus is present. The life cycles of the two types differ. S. minor does not normally produce the small mushrooms that release spores into the wind like S. sclerotiorum. Infections of lower stems and pegs develop from germinating sclerotes.

S. minor spreads by physical movement of the sclerotes. S. sclerotiorum spreads by sclerotes and by wind-blown spores.

Prevention in future crops is difficult.

Cultural
Avoid damage to plants from inter-row cultivations.

Chemical
Monitor the crop for infection, especially in cool, damp conditions. Spray with a recommended fungicide as soon as the disease is seen. Correct timing is essential to get the most effective control.

Apply registered fungicide. If the field has a history of sclerotinia, consider spraying as a precaution when the row has half closed. More than one spray may be needed.

Try to avoid the continued use of chlorothalonil to control leaf diseases in fields where sclerotinia is a problem. Continue to use chlorothalonil if the damage from leaf spot, rust and net blotch is likely to be worse than the sclerotinia.

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