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Causal organism - Oculimacula yallundae and Oculimacula acuformis (formerly Tapesia species)
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A two year break from cereals will frequently reduce inoculum in a field to a level which does not pose a serious threat to the following crop. A one year break from cereals is not sufficient to significantly reduce inoculum levels. Minimal cultivation following a cereal crop, as an introduction for oilseed rape can be used to reduce eyespot inoculum. Cereal stubble is left on the soil surface during the oilseed rape crop and is then ploughed down in preparation for another cereal crop. The infective stubble, having produced spores throughout the oilseed rape crop, is likely to pose less of a threat than inoculum on fresh stubble. Ploughing down in preparation for the next cereal crop after the oilseed rape, further decreases the inoculum risk. Ploughing releases nitrogen and can increase risk from eyespot. Minimum tillage and direct drilling can pose less of a risk from eyespot.
In the UK the resistance of winter wheat to eyespot has been derived mainly from the variety Cappelle Desprez. This confers a degree of tolerance rather than total resistance to disease. The introduction of the winter wheat variety Rendezvous in the 1980's brought a new source of resistance derived from a grass species, Aegilops ventricosa, which is now used in many breeding programmes. Varieties carrying high levels of resistance (Pch 1 gene) are now available.
The disease is very sporadic in its occurrance and so it is normally cost-effective
to apply a fungicide only when a disease threshold is reached. A threshold
of 20% tillers affected by penetrating
lesions is generally recommended although for susceptible
varieties in high-risk situations a threshold of 10-15% may be used. The HGCA
have funded the development of an eyespot risk model to help assess the need
for treatment. For many years MBC fungicides were used for eyespot control.
However the eyespot fungus quickly became resistant to the fungicide and until
1996 control of the disease relied on the use of prochloraz
(in Sportak, Sportak Alpha and Sportak Delta). Many fungicides such as Tracker(epoxiconazole+boscalid),
Proline (prothioconazole) and Unix (Cyprodinil) give high levels of control
of eyespot.
