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New diagnostic test for downy mildew

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An AHDB Horticulture-funded study into reducing the cost of downy mildew control in onion crops has resulted in a new diagnostic test which will be available for growers to trial next year.

Dr Alison Wakeham of the University of Worcester explained the scientific work which has gone into developing the MILIONCAST (MILDEW on ONION FIRECAST) model which provides predictions of downy mildew sporulation based on environmental conditions.

However this cannot determine the disease is actually present, which is where the new hand held test comes in. An in-field air sampling device is collected and, “A five minute stick test shows if the disease is present in the [air]sample and at what level. As the level of the disease increases the strength of the line depletes,” explained Dr Wakeham.

In order to prevent different interpretations of the result due to differences in people’s eyesight a reader is used, although phone apps to read similar tests are becoming available. In trials using the test and the forecast model reduced the number of spays by half while maintaining control levels of the disease.

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