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Clubroot of Cruciferous Crops

Note Number: AG0531
Published: May 2006
Updated: January 2010

 

This Agriculture Note describes clubroot, a persistent and devastating disease of cruciferous crops (i.e. cabbage, cauliflower, Chinese cabbage, broccoli, Brussels sprouts, turnip, radish and a number of leafy Asian vegetables).

Caused by

A parasite that lives in the soil. It is not fungal and not bacterial.

Scientific name

Plasmodiophora brassicae

Introduction

Clubroot is a most persistent and devastating disease of cruciferous crops. This disease is widely distributed where these crops are grown and is particularly severe in older market garden areas.

Symptoms

Infection occurs on roots at any stage of growth. Symptoms do not become obvious until knotted swellings form on the roots (Figure 1).
The first above ground symptom is usually wilting, particularly during hot-dry weather (Figure 2). Severely diseased plants are generally stunted, and the foliage may be different in colour from healthy plants.
Infected roots show characteristic swellings or knots (Figure 1). Normal root growth does not occur on severely infected taproots of young plants which form a single-clubbed root.

Biology

Survival

P. brassicae spores can remain viable in the soil for at least 20 years, even in the absence of a susceptible host.

Resting spores germinate under moist conditions and release swimming spores that infect tiny root hairs. The pathogen multiplies rapidly in the root hair and releases more swimming spores which reinfect the roots. During the secondary stage of the lifecycle, the pathogen continues to multiply within the root causing the root tissues to swell. This leads to the formation of galls which are characteristic of clubroot (Figure 1).

Infected root cells contain millions of resting spores of the pathogen (Figure 3). After the roots decay, spores are released into the soil where they remain dormant until conditions are suitable for germination, e.g. when another cruciferous crop is grown.

Dispersal

The pathogen can be spread on or in anything that may carry contaminated soil from place to place. Farm machinery, boots, animals, the dung of animals that have eaten diseased roots, and compost containing remains of a diseased crop are some of the means of spreading clubroot.

The most important means of spread is on the roots of infected transplants, contaminated irrigation water and surface flood water. Reports indicate that dam water, especially water from dams receiving runoff from infected fields, can become contaminated with the pathogen.

Spore dispersal by wind carrying contaminated dust is also possible, especially under dry conditions. Seed may become contaminated, especially if it comes into contact with contaminated water or soil.

Environmental conditions

Infection byP. brassicae depends on high soil moisture and disease development is favoured by soil temperatures between 20 to 25°C, although infection can also occur at temperatures as low as 12°C. Clubroot is more prevalent on poorly-drained soils, particularly low-lying areas.

Clubroot is more pronounced in acidic soils (pH<7.0), although at high spore concentration levels the disease can develop in alkaline soils (pH>7.0). Crop losses are most severe in warm-moist soils (generally between October to April) which are heavily infested with P. brassicae.

Host range

The pathogen infects a wide range of hosts, including some non-cruciferous plants (Table 2), however typical clubroot symptoms are only seen on members of the cabbage family.

In Victoria, clubroot has been recorded on cabbage, cauliflower, Chinese cabbage, broccoli, Brussels sprouts, turnip, radish, mustard and many varieties of leafy brassica Asian vegetables. Clubroot has been recorded elsewhere on other crops, including canola (rape), kale and swede, and also on cruciferous weeds (Table 1 and figure 4) and flower crops.

Control

Prevention

Management practices that can be used to reduce build up and spread of disease include:

Seedlings

• Use only disease-free transplants preferably obtained as cell-grown seedlings raised in a soilless or pasteurized mix, or from an open seedbed which is disease-free or pretreated with appropriate soil fumigants.
• Ensure that any equipment coming from the nursery on to the farm (e.g. seedling trays) is kept off the ground.
• Wash all traces of soil off reused trays (preferably with a high pressure wash), disinfect or steam sterilize (at least 60ºC for 30 mins) trays before reuse. Note: Plastic trays are easier to clean and disinfect than polystyrene.
• Isolate seedbed from other diseased areas and avoid contaminating the area with diseased soil or water.
• Ensure seed beds are maintained free of cruciferous weeds.
  
  

In the field

Do not use manure as a fertiliser if animals have been fed diseased roots because some spores can remain viable after passing through animals' guts.

Chemical control

There are several fungicides registered to control club root in cruciferous crops, as well as fumigants for treating seedbeds. Be sure to read label directions before use of any agricultural chemical and ensure the product is registered for the situation. For the registration status of these products, please refer to Australian Pesticides and Veterinary Medicines Authority (www.apvma.gov.au), your chemical reseller or the nearest office of DPI.

Some fungicides and fumigants require the user to hold a licence issued by DPI Chemical Standards prior to use. Please contact your local DPI office, call the DPI Customer Service Centre 136 186 or visit www.dpi.vic.gov.au/chemicalstandards for more information.

Chemical users must ensure they read and understand all sections of the chemical label prior to use.

Solarisation

Solarisation is a safe, non-chemical method for controlling clubroot, particularly for treating seedbeds (this treatment is more effective when combined with low doses of fumigants). Solarisation is only economic to use on infested land during periods of high temperature (January and February).

 Table 1. Common cruciferous weeds susceptible to infection by P. brassicae. *

Common name	Botanical name
Bird rape	Brassica campestris L.
Wild turnip	B. tournefortii. Gouan
Shepherd's purse	Capsella bursa-pastoris (L.)Medikus
Wild cabbage	Conringia orientalis (L.) Dumort
Sand mustard	Diplotaxis tenuifolia (L.) DC
Field cress	Lepidium campestre (L.) R.Br.
Musk weed	Myagrum perfoliatum L.
Wild radish	Raphanus raphanistrum L.
Turnip weed	Raphanus rugosum (L). All
Charlock	Sinapsis arvensis L.
Hedge mustard	Sisymbrium officinale (L.) Scop.
Wards wee	Vella annua L.

 Table 2. Non-cruciferous plants susceptible to infection by P. brassicae. * 

Common name	Botanical name
Creeping bent grass	Agrostis alba (L.) var stolonifera
Cocksfoot	Dactylis glomerata L.
Strawberry	Fragaria sp.
Yorkshire fog grass	Holcus lanatus L.
Perennial rye grass	Lolium perenne L.
Stock	Matthiola incana
Flanders poppy	Papaver rhoeas
Common mignonette	Reseda odorata L.
Dock	Rumex sp.
Nasturtium	Tropaeolum majus L.

Further Information

Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the DPI Knoxfield Centre.
For further information, phone Crop Health Services on (03) 9210 9222 or fax (03) 9800 3521.

For information relating to the safe and appropriate use of chemicals, including management of chemical residues and licencing requirements, call the DPI Customer Service Centre of 138 186 or visit www.dpi.vic.gov.au/chemicalstandards.

Acknowledgement

This Agnote was developed by Caroline Donald and Ian Porter, Biosciences Research Division in November 2001.
It was reviewed by Caroline Donald, Biosciences Research Division in May 2006 and January 2010.