Tailor T1 solutions to risk – South East Farmer – David Shepard
With the spring fungicide campaign underway, Hutchinsons agronomist David Shepard explains how to optimise upcoming wheat treatments ...
No two seasons are the same and spring 2022, at the time of writing at least, was milder and wetter than last year, with crops advancing strongly. Indeed, some September-sown KWS Extase had reached GS 31 by mid-March, highlighting the need to monitor crops carefully and treat fields on their own merits.
This is especially true given the mild, damp conditions of last winter which, combined with a large area of early sowing, created a higher base disease level, with mid-March forecasts from Omnia’s disease risk forecasting model predicting generally high Septoria and rust pressure.
There are four ways to optimise T1 wheat fungicide applications and maximise yield response.
Understanding which crops are at greatest disease risk is vital to prioritising applications and spray programmes. Varietal rating, drilling date and weather drive risk are all incorporated into Omnia’s disease forecasting model, which is updated fortnightly and provides a useful risk indicator across the farm from which individual treatments can be tailored.
Generally, prioritise susceptible crops rated 5 or less, but remember even robust varieties can come under pressure in bad seasons, especially when sown early.
Genetic Septoria resistance has historically been regarded as very stable, but last year’s emergence of races with virulence to Cougar resulted in some notable revisions to Septoria ratings for varieties with Cougar parentage, such as RGT Saki and KWS Firefly. These races are unlikely to disappear, so consider basing risk assessments on the one-year Recommended List rating rather than the three-year average.
Last spring highlighted the importance of accurate timing and basing spray decisions on leaf emergence rather than calendar date.
T1s are generally applied around GS 32, however the growth stage of leaf 3 emergence can vary, so dissect representative plants to confirm exactly which leaf is emerging and identify the optimum spray timing. Treat crops once most of leaf 3 is emerged to maximise coverage and protection through to T2.
The weather, disease risk and sprayer capacity should all be considered though, as waiting too long risks leaving leaf 3 exposed to infection, while spraying too early before most of the leaf has emerged could compromise coverage.
In high-risk situations, such as early-sown susceptible varieties, or where T1 is delayed, stronger Septoria chemistry such as fluxapyroxad + mefentrifluconazole is recommended. Other SDHI combinations based on fluxapyroxad offer relatively strong Septoria activity, as do some dual SDHI products such as bixafen + fluopyram.
Including the multisite folpet is a sensible anti-resistance strategy that brings extra persistence, but resist cutting the dose of mix partners to cover the cost as this compromises control. In lower disease situations, older SDHI + prothioconazole-based chemistry can be effective.
T0s should have controlled yellow rust, but in high-risk situations, build programmes around benzovindiflupyr + prothioconazole. Adding tebuconazole to Septoria-focused T1s brings quick rust control, while strobilurins such as azoxystrobin or pyraclostrobin give lasting yellow and brown rust protection.
T1 is the main time for eyespot and take-all protection, notably in early-sown second wheats. Boscalid or prothioconazole are the main eyespot options, while azoxystrobin or fluoxastrobin help reduce take-all.
Early season strobilurin application can bring useful physiological benefits to rooting that potentially improve water and nutrient use efficiency. That may be particularly beneficial for growers looking to apply less nitrogen given the high prices.
Many SDHIs, and to a lesser extent triazoles, also offer some physiological benefits.
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