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Fresh challenges for late fungicide planning – South East Farmer – David Ellerton

Further changes to yellow rust populations, combined with wide variations in drilling date and more limited chemistry, add extra complexity to fungicide planning this spring ...

Hutchinsons’ Technical Development Director Dr David Ellerton offers advice for the flag leaf.

Septoria remains the primary disease of winter wheat in most seasons, and with a large proportion of crops sown relatively early last autumn, there could be a higher risk this spring.

But while drilling date is an important factor in determining disease risk, rainfall during April and May are key to Septoria infection, so even latersown crops could come under higher pressure if conditions are conducive.

Depending on conditions over the coming days and weeks, we could well be in a high pressure situation for yellow rust and Septoria by T2, so a robust, well-timed fungicide will be vital to protect the top two leaves, which contribute approximately two-thirds of final yield.

Protecting yields

The dominance of yellow rust in 2019/20 is clearly reflected in yield responses from five Hutchinsons trials, where the largest fungicide benefits were in more susceptible varieties, including KWS Kerrin, KWS Kinetic, Skyfall and KWS Zyatt.

Normally, Septoria-susceptible varieties like KWS Barrel top the yield response chart, however last year’s uplift was around one-third of the usual level.

Across all varieties and all fungicide timings, the average response over untreated of 1.66 t/ha was below 2018/19, reflecting the dry conditions but hiding significant variations between varieties, particularly where yellow rust came in.

Close crop monitoring is therefore vital in the run up to the flag leaf spray. Use factors such as drilling date and variety disease ratings as a guide when planning spray programmes, prioritising crops with a score of six or less. But stay flexible and be prepared to react to conditions as they unfold.

T2 options

Triazoles still form the backbone of flag leaf sprays, but programmes should include actives with different modes of action, for anti-resistance and to give curative plus protectant disease control. SDHI-based products are likely to be essential in most wheat flag leaf sprays given the importance of Septoria, particularly in more curative situations where triazoles may struggle due to the sensitivity shifts seen over the past decade.

Losing chlorothalonil and epoxiconazole has reduced fungicide options this year, but there are still many effective actives and promising products in the pipeline.

Epoxiconazole will be particularly missed for yellow rust control, however tebuconazole is still very effective against yellow and brown rust, while prothioconazole offers reasonable yellow rust activity.

Prothioconazole or metconazole are also suitable for low to moderate Septoria. The former can give good activity on low to moderate mildew, too, but if mildew is well established, a specific mildewicide such as cyflufenamid may be needed.

Mefentifluconazole (Revysol) is extremely strong against Septoria and offers good rust control. SDHI options include fluxapyroxad, bixafen or fluopyram. Benzovindiflupyr is also excellent against rusts.

Where appropriate, including the protectant multisite folpet can improve Septoria control in high-risk situations and help as part of an anti-resistance strategy.

Key points

  • Early-sown crops are likely to be at higher Septoria risk
  • Beware of new rust races overcoming varietal resistance
  • Use variety scores and drilling date as a guide when planning treatments
  • Vary chemistry and modes of action for curative and protectant activity and resistance management.

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