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Rusts in ryegrass | AG0723 |
Rod Clarke, Knoxfield
November, 1999 |  |
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Crown rust
Importance:
Crown rust, caused by the fungus Puccinia coronata, is the most common and damaging disease of ryegrass. It can reduce dry matter yields by as much as 37%, root growth by depleting carbohydrate reserves, palatability, milk production in cows forced to eat infected grass and increase pasture litter on which the Facial Eczema fungus Pythomyces chartarum may grow. Rust infections in autumn can reduce plant height, as well as tillering, and thus reduce spring regrowth, by as much as 23% .
Symptoms:
Initially yellow spots develop on the leaves. Later oval orange-brown pustules 0.5 to 1.0 mm long occur on both leaf surfaces. The black spore (teliospore) stage can be found as early as September, and through the summer and autumn. Infected leaves die prematurely and severely rusted plants become stunted.
Biology:
Survival: Puccinia coronata carries-over on a range of grass hosts throughout the year.
Environmental conditions: Crown rust is favoured by warm dry days and dewy nights. These conditions are conducive to spore germination and infection of leaves.
Dispersal: Spores are spread by wind and rain splash.
Host Range: Puccinia coronata occurs on ryegrasses, wild oats, cocksfoot, tall fescue, fog grass and oats.
Control: Use resistant cultivars where available. Graze or cut infected grass before it becomes too heavily rusted. This will help remove inoculum and limit the unpalatability of the grasses. Fungicides could be considered for valuable seed crops, but not for general grazing pasture.
Stem rust
Importance:
Stem rust is caused by the fungus Puccinia graminis. and occurs on stems and leaves. Stem infections can decrease seed yield by up to 50% by restricting the flow of nutrients to the head thus reducing seed weight, and numbers per spike. Seed crops may become uneconomical to harvest. Stem rust is reported to be more of a problem in the late maturing cultivars.
Symptoms:
Reddish-brown elongated, 1-10 0.5-2 mm pustules with ragged edges occur on the leaves, stems and seed head. Later in the season the pustules may turn black when the fungus produces a resting stage spore (teliospore). These spores, in Australia, have no further part in the life cycle of the fungus.
Biology:
Survival: Puccinia graminis carries over on a range of grasses and cereals.
Environmental conditions: Free moisture on the leaf surface is required for spore germination and infection. Such conditions occur following dew or light rain. Disease development is most rapid at temperatures between 15° and 22°C.
Dispersal: Spores of Puccinia graminis may be wind-borne over substantial distances.
Host Range: Puccinia graminis occurs on ryegrass, phalaris, wheatgrass, blowngrass, wild oats, cocksfoot, quaking grass, barley grass and cereals.
Control: Use resistant or less susceptible cultivars where available. Graze or cut infected grass before it becomes too heavily rusted. This will help remove inoculum and limit the unpalatability of the grasses. Fungicides could be considered for valuable seed crops. Spraying should be applied at the first sign of stem rust and not left until infection is severe, by then the damage is done.
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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