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Diseases of white clover - 2: fungal diseases | AG0732 |
Rod Clarke, Knoxfield
November, 1999 |  |
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Clover rot
Importance:
Clover rot is caused by the fungus Sclerotinia trifoliorum. The incidence and severity of this disease varies from year to year and paddock to paddock, but does occur in most years. There may be just scattered plants affected or when severe, whole paddocks. Outbreaks of clover rot are most frequent and damaging in irrigated pastures where as much as 25-50% of a stand can be affected. Seedlings are particularly susceptible to this disease.
Symptoms:
Small (less than 1 mm), brown spots, which expand and join together, develop on the leaves, causing them to wither and drop off. The fungus also infects the stems and shoots causing the plant to collapse and die. A severely affected patch of pasture can be a mass of rotting plant material on the ground. Dead leaves and stems can be covered by a white mould, and small (slightly larger than a pinhead), black, irregularly shaped, resting bodies (sclerotia), which are characteristic of this disease.
Biology:
Survival: The black resting bodies, sclerotia, enable the fungus to survive the hot summers on plant debris or in the soil, where they can survive for at least 5 years.
Environmental conditions: Cool, moist weather and luxuriant plant growth are ideal conditions for the development of this disease.
Dispersal: Under moist conditions, in autumn, the sclerotia germinate to produce a saucer shaped spore bearing body (apothecia). The spores are ejected from this body and are carried onto nearby leaves by wind to set up the initial infection. Secondary spread is via fungal growth from plant to plant.
Host Range: S. trifoliorum occurs on lucerne, red clover, subterranean clover and vetch as well as white clover.
Control:
Close grazing of clover in the autumn and early winter will slow the spread of the disease by reducing the humidity within the stand.
Deep ploughing will bury sclerotia and reduce their chances of germinating.
Use seed that is free of sclerotia.
Use rotations of at least 4 to 5 years between susceptible crops.
There are no resistant cultivars.
Grey mould
Importance:
Grey mould is caused by the fungus Botrytis cinerea. It is a minor disease of white clover which affects scattered plants or patches of plants up to several metres in diameter, but never a whole stand.
Symptoms:
The fungus infects the stems and shoots causing the plant to collapse and die. A severely affected patch can be a mass of rotting plant material similar to that of clover rot. Dead leaves and stems, under moist conditions can be covered by a growth of furry grey mould and spores, and small (slightly larger than a pinhead), black, irregularly shaped, resting bodies (sclerotia).
Biology:
Survival: The fungus can survive on infected plant debris, seed and as resting bodies (sclerotia) in the soil.
Environmental conditions: Cool moist conditions and lush growth, favour the development of grey mould. Plants damaged by frost or other means are susceptible to infection.
Dispersal: Large numbers of spores in the grey furry mould are rain splashed over relatively short distances or wind blown over several kilometres.
Host Range: Botrytis cinerea has a wide host range including white clover, red clover, subterranean clover, lupin, chick pea, field pea, sunflower and paspalum.
Control:
Close grazing of clover in the autumn and early winter will slow the spread of the disease by reducing the humidity within the stand.
Deep ploughing will bury sclerotia and reduce their chances of germinating.
Use seed that is free of sclerotia.
Use rotations of at least 4 to 5 years between susceptible crops.
Wart disease
Importance:
Wart disease is caused by the fungus Physoderma trifolii and usually causes little economic loss due to the fact that the disease only assumes epidemic proportions under conditions of excessive moisture.
Symptoms:
Galls or swellings about 5 mm in diameter develop on the leaves, stems and flowers. The galls often join and this causes a twisting and distortion of the affected parts.
Biology:
Survival: Physoderma trifolii can carry-over by means of resting spores within the galls.
Environmental conditions: The disease usually occurs in locally wet areas, such as river flats or on heavy poorly drained soils.
Dispersal: Under excessively wet conditions the galls decay and the resting spores release zoospores which move to infect nearby plants.
Host Range: Physoderma trifolii occurs on subterranean clover, red clover and white clover.
Control:
Improve irrigation management and surface drainage to reduce excess water lying in bays.
Rotate paddock out of pasture legumes for a number of years, if disease continually occurs.
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.
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