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Clover scorch disease of subterranean clover | AG0725 |
Rod Clarke, Knoxfield
November, 1999 |  |
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Importance
Clover scorch is caused by the fungus Kabatiella caulivora and mainly occurs in areas receiving between 500 and 650 mm of rainfall each year. It has not been recorded in Gippsland where similar rainfall is recorded. In the 1970's when there were many susceptible cultivars of subterranean clover (eg. Yarloop and Wooginellup) in use, losses due to this disease were extremely high. Whole paddocks of subterranean clover could collapse in just three weeks, making them uneconomical to cut for hay or harvest for seed.
Symptoms
The first signs of clover scorch are usually seen in early September, although symptoms have been seen as early as mid-June. At first, patches of plants, up to one metre in diameter, wilt and show a scorching of the leaves. The leaves hang down from the petiole to give a characteristic "shepherd's crook" appearance. Individual leaflets often twist so as to expose the undersides, which is the case with Yarloop, giving plants a silvery-white appearance.
Elongated, brown, sunken lesions develop on the petioles, runners and at the junction of the leaflets. As the lesions extend, the petioles are girdled, causing the collapse of the leaf. The remaining petiole can often be seen protruding above the stand after the leaves die. As the plants dry out the whole paddock may appear scorched.
Biology
Survival: The spores of the fungus carry-over on infected plant debris.
Environmental conditions: Clover scorch is most severe in dense clover stands that have been locked up for hay or seed production. It also occurs in open pastures, despite grazing. Mild, humid and wet conditions are ideally suited to the development of clover scorch.
Dispersal: Spores are primarily spread by wind driven rain-splash, as well as livestock and probably insects. Infected material on hay cutting equipment can spread the disease from one paddock to the next.
Host Range: Kabatiella caulivora occurs on subterranean clover, berseem clover, and red clover in the northern hemisphere ("northern anthracnose").
Control
Use resistant or tolerant cultivars.
At the first sign of clover scorch in a stand closed up for hay or seed production, graze or cut for hay as soon as possible to minimise losses and reduce the humid conditions within the stand that favour disease development.
Use preventive or curative sprays of benomyl or carbendazim, particularly on hay or seed crops. The economics of doing this should be carefully considered.
Preventive sprays (lower rate) should be applied 2 to 3 weeks after closing up, about mid September.
A second spray could be applied 4 weeks later in mid October if weather conditions favour disease build-up.
Curative sprays (higher rate) could be applied if the disease has established at closing-up time. A second spray could be applied 4 weeks later if the disease develops further.
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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