No second chance on LLS azole rates

With the latest Light Leaf Spot (LLS) forecast predicting high disease pressure for all regions Bayer’s Tim Nicholson is advising growers not to take any chances with azole rates. He says persistence is vital as crops need to be protected until growers have the opportunity to get back in ahead of stem extension.

“There’s no second chance with LLS as even the most effective actives offer no real curative option. If the disease is established ahead of stem extension then yield losses can be substantial,” he cautions.

That’s why Mr Nicholson is now advocating robust rates of the most active products, prothioconazole and tebuconazole. “Last season we saw significant stem and pod infection so it was perhaps inevitable that we would see high disease pressure this autumn. Under such conditions using less effective chemistry or reducing rates will be a risk.

“With very high LLS pressure being forecast no programme will be effective unless it contains the most potent LLS actives. When targeting LLS it is critical to use a proven LLS effective fungicide, otherwise you could run the risk of the disease becoming established through the winter,” he warns.

His preferred course of action is a 0.46 L/ha rate of Proline275 (prothioconazole). “Even with a number of forward crops it’s now too late to get the full benefit from autumn growth regulation. Where this needs to be addressed I would hold back straight tebuconazole until stem extension. Also, growers don’t want to compromise autumn disease control. Following a dry September many crops are about to reach Phoma thresholds as well so growers need to be selecting actives that are effective against both diseases, and that’s prothioconazole,” he says.

He believes that is critical now given the spread of LLS over recent years. “Favourable weather, the intensity of OSR rotations and lack of varietal resistance means that many growers now face the twin threat of Phoma and LLS in their OSR crops.With the dry conditions in September delaying the onset of Phoma, and the disease only appearing in the crop more recently, it is important to increase the rate of Proline275 from 0.32 L/ha up to 0.46 L/ha”.

“In both Bayer and independent trials we see dose responses in all but the lowest disease situations and I would suggest that upping rates of Proline275 for late autumn applications is worthwhile given the combination of Phoma and LLS threat this season,” he concludes.

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