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Paspalum leaf blight | AG0722 |
Rod Clarke, Knoxfield
November, 1999 |  |
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Importance
Paspalum leaf blight, caused by the fungus Ascochyta paspalii, occurs from September to May each year. This disease was discovered at Strathmerton in 1978, and since then it has been detected throughout the flood irrigation perennial pastures of northern Victoria and southern New South Wales. The leaf blight can reduce paspalum dry matter production by up to 50% with the average loss being 20%.
Symptoms
Symptoms are often difficult to detect, especially if the pasture has been recently grazed. It is usually three weeks after grazing when symptoms start to develop.
The first symptom of paspalum leaf blight is a blue/grey discolouration, with a light brown margin, extending from the leaf tip and usually confined to one side of the midrib. Within a few days the affected area changes through an ashy-grey to a light brown straw colour, and tiny, pin-prick sized black spore producing fruiting bodies (pycnidia) appear. Within a few days the whole width of the leaf may he affected and the symptoms will spread longitudinally down the leaf with a yellow to light-brown margin between healthy and affected areas.
Biology
Survival:
Ascochyta paspalii over winters in the paspalum roots, crowns, leaves and seed.
Environmental conditions:
A leaf wetting period of 12-24 hours (irrigation), high humidity and temperatures between 20° and 30°C favour disease development.
Dispersal:
Spores from the fruiting bodies on the leaves are rain splashed to nearby plants. These spores may also he transferred from plant to plant in the saliva of grazing animals.
Host range:
Ascochyta paspalii occurs only on Paspalum spp.
Control
There is no known control for this disease at present. Do not move grazing animals from infected to healthy paddocks. The animals should be moved onto a ryegrass/clover pasture before going onto healthy paspalum. If paspalum is to be sown into a paddock, use seed from a disease free stand. Applications of nitrogen will help boost production of diseased paspalum, but will not reduce disease levels. Fungicides have been found not to be effective against this disease.
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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