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Crop Advice & Expertise

South: Disease control a priority in the South this April

Kent-based Nick Lewis offers some advice on how to protect cereal and oilseed rape crops from foliar disease this month

This month’s key messages

  • Don’t stretch the gap between T0 and T1 applications in winter wheat
  • Dissect main stems to ensure T1 is targeting final leaf 3
  • SDHI-azole plus chlorothalonil best option at T1 timing
  • Siltra the strongest T1 product on barley disease
  • Only use chlorothalonil at T1 in winter barley if crop is stressed
  • Use an OSR flowering spray that protects against sclerotinia and light leaf spot

Crop progress

The weather has largely played ball over the last month, with no extremes of cold, dry or wet. This has seen winter crop growth to continue unchecked and there is plenty of yield potential across the South. Growers have also been able to travel and apply nitrogen, grassweed herbicides and continue with spring drilling with little delay.

The only major problem this spring is cabbage stem flea beetle larvae in oilseed rape crops, with damage very localised but severe in some cases. Hotspots seem to be more abundant in the West of the region, with Kent in the South East less affected.

 

Nick’s agronomy tips for April

1. Apply a T0 fungicide no more than 2-3 weeks before T1

Although weather has been relatively dry through March, foliar diseases such as Septoria is present in winter wheat crops. If it turns wet during April, it could be a high disease year and applying a T0 fungicide will help suppress inoculum until the important T1 timing. Prioritise earlier drilled crops and varieties with low Septoria resistant scores.

A T0 of multisite chlorothalonil should be minimum for Septoria protection, adding in other actives such as a strobilurin or specific mildewicide where rust and mildew are a problem. Do not use any primary azoles, such as epoxiconazole or prothioconazole, at T0 to avoid selecting for resistant Septoria strains.

Timing is also key – get out in the field and check growth stages and apply any T0 sprays no more than 2-3 weeks ahead of an expected T1 timing, when final leaf 3 is fully emerged.

2. Make sure final leaf 3 is targeted at T1 timing

Some of the more forward wheats will reach the T1 fungicide timing later in April. Timing of sprays is a crucial element of disease control – growers should get out into the field and dissect plants to ensure product is applied to the correct leaf. In the case of T1, that is final leaf 3.

In terms of product choice, going down a non-SDHI (succinate dehydrogenase inhibitor) fungicide route is an option, but I would argue it is better to include one at T1. The SDHI will help support the azole and if timing is correct, the inclusion of chlorothalonil will help with resistance management too.

In a low-pressure situation, 1L/ha of Aviator (bixafen + prothioconazole) is good choice. Where disease risk is higher, 1L/ha of Ascra (fluopyram + bixafen + prothioconazole) will provide a more robust option. Consider omitting chlorothalonil when using Aviator if used in a more curative situation – this is less of a concern with Ascra.

3. SDHI-azole fungicide well suited for barley T1s

Winter barley crops are at a spread of stages, but the majority will be ready for a T1 fungicide application in the first week on April. An SDHI-azole combination is well suited to this timing, with Siltra (bixafen + prothioconazole) the best of the options available.

There is a debate on whether multisite chlorothalonil should be used at T1 in barley for ramularia, because it is the only effective fungicide available for its control. The disease can go unseen for much of the season, only expressing itself when crops are stressed or after flowering. If the crop is stressed at T1 the addition of chlorothalonil is an option, but otherwise growers will see the greatest benefit at T2.

4. Plan flowering sprays in oilseed rape

Oilseed rape crops are approaching flowering and will soon require a fungicide treatment. Proline (prothioconazole) is an important product at early to mid-flowering, not only protecting the crop from sclerotinia infection, but also helping to prevent light leaf spot moving up the canopy. If the crop is still flowering three weeks later, a second application may be required to maintain sclerotinia protection until all petals have fallen.

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