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Crop Advice & Expertise

Scotland: How to formulate crop fungicide plans this May

James Howat provides some timely advice on controlling disease in wheat, barley and oilseed rape

This month’s key messages

  • A robust wheat T1 fungicide provides spray timing flexibility if delayed
  • Aviator or Ascra are best options and adjust rates based on septoria risk
  • Check for eyespot and use a prothioconazole-based T1 product to negate threat
  • First sclerotinia sprays should be applied to OSR as soon as possible
  • Follow up with second spray three weeks later if risk remains high
  • Use chlorothalonil to negate ramularia threat in winter barley
  • Conisder taking advantage of successful SpotCheck service next season

Crop progress

Wheat crops are approaching the T1 fungicide timing and growers will soon be setting off with the sprayer to get those recommendations applied. Most winter barleys will now have had T1 sprays, bar the odd late-drilled crop.

Oilseed rape is about 80-100% flowering and looking very well after avoiding all the cabbage stem flea beetle damage crops have been subjected to further south.

With the high temperatures in late April and relatively little rain over recent weeks, things have dried out, but drought stress is far from being a concern yet. It does mean that disease levels in most crops are low heading into May.

 

James’s agronomy tips for May

1. Use appropriate product and dose for T1s in wheat

Levels of Septoria in wheat crops are lower than expected across the region for this time of year. While a non-SDHI approach to imminent T1 applications can provide good control of the disease, timing needs to be spot on. Inclusion of an SDHI will provide more flexibility if the sprays are delayed due to weather or other unforeseen issues.

Where there is less disease pressure, I would recommend a T1 of 1 L/ha of Aviator (bixafen + prothioconazole). Where there are obvious signs of disease and risk is higher, a Rolls Royce treatment of Ascra (bixafen + fluopyram + prothiconazole) at 1-1.2 L/ha is available. A multisite such as chlorothalonil or folpet should also be included.

If you use robust products and rates at T1, it may present opportunities to reduce spend at T2 if the weather remains dry. I am an advocate of “front loading” programmes in this way to get on top of disease early.

2. Check for eyespot and treat at T1 where present

A common theme from Bayer’s Crop Doctor tours in recent weeks has been the presence of eyespot in wheat crops. I would urge growers to get out into crops ahead of T1 applications and check plant stem bases for the disease. The best and most effective products to control stem-based diseases are prothioconazole-based and a 75% dose of the active at T1 will give control of both eyespot and fusarium.

3. Use risk forecast to determine one- or two-spray sclerotinia strategy

If growers have not applied a flowering spray to oilseed rape crops already, a 0.46 L/ha dose of Proline (prothioconazole) should be used as soon as possible. This will protect against sclerotinia and have activity on any light leaf spot in the crop, preventing it from moving up the canopy.

If crops are still flowering three weeks after the first application and sclerotinia risk remains high, a follow up treatment should be applied. Use the AHDB sclerotinia risk map to inform this decision. For second sprays, a lower rate of Proline at 0.32 L/ha is adequate, as later sclerotinia infection is less damaging to yield. Be careful not to exceed the maximum total dose of 1.25L/ha if used at earlier timings.

4. Consider a multisite fungicide to protect against ramularia in barley

Winter barley T1s will be complete as we head into May, so attention will turn to late plant growth regulators at GS37-GS39. Where going through the crop with a plant growth regulator, it might be worth considering adding chlorothalonil to control ramularia, a disease which SDHIs, azoles and strobilurins now struggle to suppress.

A more traditional T2 spray will follow as awns emerge and chlorothalonil is also advised at this timing to maintain protection, alongside an SDHI-zole product such as Siltra (bixafen + prothioconazole). Check chlorothalonil product labels to ensure a late application is permitted, as cut-off dates do vary.

5. Use SpotCheck service next season for integrated OSR disease management

Since its launch in 2017, the collaborative SpotCheck initiative run by ADAS and Bayer has been a big success. It allows growers and agronomists to send in oilseed rape leaf samples to the ADAS laboratory and test for the presence of light leaf spot.

There were over 650 samples sent in this season from across the UK, representing a significant year on year increase. These provided a valuable insight into disease pressure, especially light leaf spot ahead of key spring fungicide timings.

This great tool helps inform management decisions and should be considered next season as part of an integrated light leaf spot control strategy.

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