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Take an integrated approach to managing disease risk – South East Farmer – James Short

This season has clearly shown how early drilling can increase pressure from Septoria and other wheat diseases. Hutchinsons' James Short examines how to manage such risks this autumn ...

The variation in drilling dates caused by rain interruptions last October has highlighted some clear differences in disease development between early and late-sown crops this year.

After a dry start to the spring, the rain came in April and in some areas of Kent it has not yet stopped. The amount of rainfall in these areas during June has been exceptional – and many early-sown wheats have come under significant Septoria pressure even where robust flag leaf sprays were applied, proving that underlying infection risk never really disappears.

Warm, wet conditions in May triggered this late surge, but it may have been exacerbated where T0 and T1 fungicides were scaled back during the cool, dry conditions earlier in spring. The loss of chlorothalonil from programmes, and any extended gap between T1 and T2 sprays, could also have played a part.

Whatever the reason, it reinforces the threat Septoria poses when drilling early, alongside eyespot, Barley Yellow Dwarf Virus and take-all, albeit to lesser extents. Mildew and yellow rust are typically more problematic in later-sown crops, although the appearance of new, aggressive yellow rust races continues to make it less predictable and harder to control.

Tailoring sowing dates

Drilling later is a very effective way of reducing Septoria risk, as moving from mid-September sowing to mid-October can be equivalent to gaining an extra point on a variety’s resistance rating. For example, a crop of end-September sown KWS Extase (rated 8) may be at similar Septoria risk to November-drilled KWS Firefly (6.8).

But with recent wash-out autumns still fresh in mind, this must be balanced against the need to get crops in before the weather breaks. The key is to tailor variety choices to drilling date and the subsequent risks crops will face throughout the season, from disease to lodging, so protectant programmes can be planned and fields prioritised for treatment well in advance.

Variety ratings are a good starting point to indicate inherent susceptibility, and generally it is best to opt for those rated 6+ for Septoria if drilling early.

But consider other factors too, such as treated and untreated yields, lodging susceptibility, eyespot rating, speed of development and rust scores. We saw last year how quickly new rust races can overcome varietal resistance; this year the pressure is on Septoria, so treat the present RL ratings with caution.

The South East tends to be dominated by Group 1, 2 and 3 (biscuits), but continue to aim for a balanced portfolio of varieties and drilling dates to spread the risk.

Omnia’s disease modelling function is a valuable tool for assessing disease risk and planning for the season ahead. It uses accurate data from various sources to give a clear colour-coded indication of risk, based on three main factors; the responsiveness of varieties to fungicides, the impact of drilling date on disease risk and the influence of weather on inoculum build-up.

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