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Sclerotinia white rot of french bean

Note Number: AG0549
Elizabeth Minchinton & Kathy Pullman, Knoxfield July, 1996
Updated: December 1999

Scientific name

Sclerotinia sclerotiorum

Figure 1. Sclerotinia sclerotiorum on beans in the field.

Figure 1. Sclerotinia sclerotiorum on beans in the field.

Introduction

White rot is a destructive disease caused by a fungus which can infect all above-ground parts of french bean plants. This disease infects flowering crops, especially when the weather is cool and moist and the crop canopy is dense.

Symptoms

A watery-brown soft rot develops, followed by a white-cottony mould. Stems, leaves, flowers and pods may be affected and stem infections near soil level lead to plant collapse. Black, seed-like resting bodies called 'sclerotia' develop in the mould or in the stem pith (tissue located in the centre of the stem).

Disease development

Plants are susceptible at all ages, but most infection occurs on beans during and after flowering. Air-borne spores (ascospores) infect old and dying flowers then the fungus grows into neighbouring tissues and organs, which are rapidly killed. Infected flowers falling onto leaves and branches will also spread the disease within a crop. White rot may also develop on pods in transit and storage.

Biology

Figure 2. Sclerotinia sclerotiorum on beans after harvest.

Figure 2. Sclerotinia sclerotiorum on beans after harvest.

Survival

The sclerotia can survive in the soil for over five years. Sclerotes in the top 10 cm of soil germinate after exposure to cool moist conditions.

Dispersal

Air-borne spores are the most important means of spread and infection. Spores are ejected from the apothecia (small, orange, cup-like structures produced by the seed-like sclerotia) and are dispersed by the wind over many kilometres. The fungus can also be transmitted through infected seed, irrigation water or plant to plant contact.

Environmental conditions

The fungus likes dense plant canopies, prolonged-high humidity and cool wet weather. White rot develops at temperatures ranging from 5-30 C, with an optimum of 20-25 C.

Host range

Phaseolus vulgaris (bean) and a large range of crops, eg Brassica, sunflower, safflower, coriander, melon, tomato, lettuce and cucumber.

Control

  • Do not over irrigate, and avoid irrigation in the afternoon.
  • Spray with a registered fungicide during flowering.
  • Avoid planting dense crops.
  • Plough in infected crop remains deeply.
  • Rotate crops with at least a four-year break between beans.


Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the Institute for Horticultural Development (IHD). For further information, phone Crop Health Services on (03) 9210-9222 or fax (03) 9800 3521.
For further information on registered chemicals, phone NRE Chemical Information Service.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.