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Controlling onion white rot

Onion white rot Fruitfed 2022

Controlling onion white rot

Onion white rot can cause significant loss to onion crops in all major growing areas around the country. Caused by the fungal pathogen Sclerotium cepivorum, white rot symptoms are seen as fluffy white growth on the roots and base of an onion. Above ground symptoms include stunted growth, wilted appearance and characteristic yellowing of the leaves.

Numerous black sclerotia form on infected tissue, creating hard masses of fungal threads which are the resting bodies of the disease. In this sclerotia form, white rot can remain dormant in soil for many years making control difficult. Crop rotations of two to three years do not lessen disease pressure and even longer rotations do not fully rid a paddock of the disease.

The most effective control measure is to apply a fungicide at the time indicated by the onion white rot disease prediction model, which measures soil temperature and calculates cumulative degree days from planting. By using the model, growers can time fungicide application 100 to 150 degree days from planting. Without intervention, the first infected plants can be found 250 degree days from planting.

Several effective fungicides are available, so consider the maximum number of applications allowed for the different chemical groups, and their recommended use pattern. Sercadis® is a strong option, having performed well in Fruitfed Supplies trials in recent years. This product can be rotated with DMI and QoI options.

When creating your onion white rot control strategy, consider:
Seed coatings containing SDHI fungicides count as one of the three SDHI applications allowed per crop. Remember there is a maximum of two applications of the same SDHI active per crop.
Export market Maximum Residue Levels (MRL) which can change from season to season, so communicate with your exporter.

For more information regarding product selection or the white rot disease prediction model, please contact your local Fruitfed Supplies Technical Horticultural Representative.

Article written by Daniel Sutton,
Technical Specialist – Vegetables

ACVM Registration Number: Sercadis® #P008977. Read the registered label before use.