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Crop Advice & Expertise

What’s happening in fields in the South West this May?

It is all about keeping on top of high disease pressure for Tim Nicholson this month as he offers advice on fungicide programmes in cereal and oilseed rape crops.

At a Glance

This month’s messages:

 

  • Apply Liberator to late-drilled spring barley crops where meadow grass is a problem
  • Take a preventative approach to disease control in spring barley with an early spray
  • Always include CTL in barley T2 applications for ramularia control
  • Septoria pressure is high so use an appropriate SDHI-azole formulation based on varietal susceptibility
  • Light leaf spot and sclerotinia pressure is high in OSR crops
  • Invest in a two-spray flowering fungicide programme for maximum yield

Spring barley

It was very wet in the South West through much of April and was difficult to get on the land to do any groundwork and establish spring crops. However, after the 20th it dried up for 7-10 days and the remainder of the planned spring barley area was planted and those crops are now beginning to emerge.

If you are expecting problems with annual meadow grass on those sites, it is wise to apply 0.3L/ha of Liberator (flufenacet + diflufenican) on an Extension of Authorisation for Minor Use (EAMU). The flufenacet component is key to good meadow grass control and can be applied up to GS24.

Earlier-drilled spring barley is now approaching mid-tillering and will soon require its first fungicide. At this stage, there is no visible disease in the crop, but a preventative approach is crucial and an application of 0.4L/ha of Siltra (bixafen + prothioconazole) or 0.75L/ha of Fandango (fluoxastrobin + prothioconazole) at mid-late tillering will help keep disease out.

Winter barley

Winter barley is racing through the growth stages and T1 fungicides have been applied. The next application at T2 (GS 39-49) will be going on soon and it’s important to remember that ramularia is a UK-wide problem. Due to reduced sensitivity to other actives, only chlorothalonil can be relied on against the disease now. Any applications of SDHI- or strobilurin-azole combinations, such as Siltra or Fandango, must include CTL at T2.

There is also partial insensitivity to SDHIs and strobilurins in net blotch populations. Prothioconazole is strong on the disease, and ensures Siltra or Fandango will do a good job.

Often growers will aim to get some fungicide on the peeping awns at the T2 stage. It is likely that the T1-T2 interval will be short this season so that should be achievable but if it exceeds four weeks, the T2 should be brought forward to from GS39.

Winter wheat

With T1 fungicides already applied in the South West, thoughts are turning to the T2 timing. There is little in the way of rusts present, but there is a high level of septoria tritici which has the potential to splash up onto the top two leaves. I would estimate that flag leaf emergence will be around 20 May, but it is important to take account for differences across drill dates and varieties to get the T2 timing correct.

For varieties rated at 6 or above for septoria, an application of Aviator (bixafen + prothioconazole) will be sufficient, but on the more susceptible varieties below a score of 6 Ascra (bixafen + fluopyram + prothioconazole) at a 1.2L/ha rate is a better option.

In addition, some septoria isolates have become slightly less sensitive to the pyrazole-4-carboxamide class of SDHIs, which includes all the SDHI wheat fungicides introduced in the last 6 years or so, including bixafen. Ascra has the addition of fluopyram, which is from the pyridinyl-ethyl benzamide class, so will kill a broader range of septoria isolates. However, a high rate of an effective azole, as is the case with Aviator and Ascra, is also vital to protect the SDHIs.

If using products formulated to get inside the leaf, such as Aviator, the inclusion of chlorothalonil at T2 could compromise any curative activity required on final leaf 2, which will have been unprotected for about two weeks by GS39. With Ascra, we have seen neutral or positive results from its inclusion, and some may favour its use. With both Xpro products, the Leafshield formulation is rainfast in minutes, so will give you the chance to take every spray opportunity and peace of mind once the sprayer has left the field.

Oilseed rape

Crops have been in flower for some time in the region and weather has been conducive for sclerotinia, with showers also helping infected petals to stick to leaves. Prothioconazole offers a cost-effective treatment for sclerotinia. With light leaf spot still present in some crops and rain splashed conidia and wind-borne ascospores helping to spread the disease, it will also help reduce infection.

Some of the first sclerotinia sprays are already on, but where they haven’t been applied, get them on before petals start to fall and follow up three weeks later if crops are still flowering. From the Yield Enhancement Network (YEN), we have seen that it is important to maximise photosynthesis post flowering to ensure the crop sets a high number of seeds and fills them for maximum output. Investing in a comprehensive two-spray flowering programme will help set up the crop for high yields.

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