The Australian horticultural brassica industry grows produce valued at $134 million annually.
Broccoli, cauliflower and cabbage are the major brassica
vegetable crops. Minor crops include Brussels sprouts, Chinese cabbage and Asian brassica vegetables.
Clubroot is the most serious soilborne disease affecting brassicas world wide. It is caused by
Plasmodiophora brassicae Woronin, an obligate biotrophic parasite. Currently considered to belong to
the Protoctista, it is neither plant, animal nor fungus.
Clubroot was first reported in Australia in 1890. It is likely to have been brought into the country with
the early settlers as diseased planting material, although fodder or grazing
animals represent an alternative source of contamination.
Recent increases in the prevalence of this
disease can be associated with the increased use of transplants, narrow rotations, more extensive
cropping on the same soil (in some cases, 4 crops per year) and the suspected increased movement of
the pathogen on trucks, bulk bins and other farm equipment.
Surveys have shown that over 70% of brassica properties in Victoria are affected
Crop losses of up to 25 hectares/property have been reported and total national crop loss
is estimated at between 5 and 10% of brassica production.
Clubroot is endemic in most of the major production regions of Victoria, New South Wales and
Tasmania. Outbreaks have occurred in Stanthorpe (Queensland in 1997), Gatton, (Queensland in
2001) and Manjimup (Western Australia in 1993).
Clubroot is now a significant problem in every state
Symptoms of disease are restricted to members of the family Cruciferae.
Infection can occur at any stage of growth and is restricted to the roots.
Infected roots swell forming characteristic galls that may either be large and compact or numerous irregular swellings, depending upon the timing and severity of infection.
Infected plants are nutritionally impaired as galled roots have a reduced capacity to assimilate water and nutrients from the soil.
The earliest above ground symptom of clubroot is wilting of the leaves of infected plants particularly on warm days.
Severely infected plants will be stunted and yield significantly reduced.
The results presented in this report serve as a small snapshot of activities undertaken in the field for the duration of the project.
During this time two new treatments have been developed, reports from individual states have been tested nationally and large numbers of growers have participated in field displays and demonstrations.
The following generalisations can be made:
- Application of lime as calcium oxide (to increase pH to 7.0-7.5 in responsive soils) is a ‘good value for money’ treatment consistently returning a profit from most field sites nationally.
- Shirlan (fluazinam) applied at 3 L/ha effectively controls clubroot but must be evenly distributed around the transplant root zone at planting.
Lower rates (2-3 L/ha) may suffice in the Manjimup district of Western Australia.
- Banded incorporation of Shirlan (3 L/ha) at planting is the most effective method of application of this fungicide.
- Banded incorporation of a very low rate of calcium cyanamide has reduced the cost of treatment from $1600/ha to $112/ha.
- A new fungicide flusulfamide (Nebijin) applied with Du-wett (a wetting agent) has provided good control of clubroot at 0.6 mg/plant in Victoria and Queensland.
In these states control has been on par with that provided by Shirlan. The effective rate is twice that recommended by the New Zealand based suppliers (the recommended rate being ineffective).
No residues were found in treated produce and negotiations for registration and distribution in Australia are underway.
This result was not repeated in Western Australia and the reason for the failure of the product to control clubroot in this state should be further investigated before registration.
Financial support for this research has been provided by: Horticulture Australia Limited, the vegetable
growers R&D levy and Stae Departments of Agriculture.
Thanks to the following growers for their assistance with trial work:
| Sam Calameri
|| Kevin Temple
||WU Yue Fang,
||ZHONE Cai Xia
|Ha Sau Ying
||XIANG Cai Ji
Thanks to the following for their technical assistance on the project:
|Chang You Pan
| C. Haase
Statistical advice by Fiona Thomson and Nam Ky Nguyen (Department of Primary Industries, Vic).