How to manage crop development and disease pressure this spring?

For some, the variability will be reminiscent of last season, with many early-sown forward wheats showing good growth and excellent potential, while some later-drilled crops have struggled to get going in cold, wet soils.

Essex and Suffolk-based Farmacy agronomist, Tom Smith, said that some of the most forward wheats in his area were up to growth stage 25 at the time of writing in mid-February, with the majority around GS 23/24, while those drilled in mid-November after potatoes were back nearer GS 13.

Mr Smith added: “These are the extremes, but there’s a lot of variability out there, which poses challenges for early fungicide planning, and reinforces the importance of applying treatments according to growth stage, not calendar date.

“Growers also need to recognise that later, backward crops, often go through growth stages quickly as temperatures and day length increase, potentially complicating spray timings.”

The expert added that late-drilled wheats can often be the trickier crops to manage, especially if rapid growth results in weaker stems and increased lodging risk.

Protect potential

Head of integrated crop management, David Howard, explained that both forward and backward crops need managing carefully to protect and build potential, which all starts with the T0.

“We have seen before that growers can sometimes be reluctant to invest too much in thinner crops, cutting back on early T0 and T1 sprays, only to find they then had to chase disease hard at T2 to get it back under control,” he said.

Yellow rust in particular can be more pronounced in late-sown or stressed wheats, and thinner crops are also more reliant on lower leaves to help them catch up, therefore, protecting photosynthetic capacity is key, despite the potentially lower yield potential, Mr Howard added.

With recent seasons indicating rust and Septoria are becoming more aggressive and better adapted to changing weather patterns, effective early disease control is vital to stay on the front foot in any crop.

The expert said: “The T0 fungicide may not offer the same yield responses as later treatments, but it sets the foundations for effective disease management, and crucially, helps manage the pressure on subsequent GS 32 (T1) treatments and key yield-building leaves.”

Rust focus at T0

Historically, Septoria was the main target at T0, and while Septoria control remains important in high-risk varieties and regions – particularly the West and South-West – for many, the focus has shifted towards managing rust, Mr Howard said.

“Last year saw a particularly early appearance of brown rust in some crops, and after a high-pressure season, there could be more inoculum around this spring, although much depends on the impact of winter frosts in reducing inoculum, or at least delaying onset. Equally, milder conditions, like last season, could result in earlier rust pressure.

“Rust management is a numbers game; you must act early to slow it down before inoculum builds. An effective T0 is a ‘no-brainer’ for anyone growing wheat in higher rust-risk areas of eastern counties,” he added.

Mr Smith agrees. He said: “While there has been a bit of Septoria bubbling away on older leaves, we’ve not seen much yellow rust in crops so far, but that could change quickly once conditions warm up. Although we did have a cold spell during January, conditions in this area have generally been quite mild through the autumn and winter, so inoculum is still likely to be there.”

In most situations, Mr Smith said that tebuconazole is his preferred option for controlling yellow rust at T0, in combination with a strobilurin such as azoxystrobin for extra persistence. For those looking to boost Septoria protection, consider including a multi-site like folpet, he noted.

“As always though, fungicide choices should be based on individual situations, considering things like variety, growth stage, previous cropping, drilling date, the weather, and what disease(s) you’re seeing in the field at the time.”

Growth manipulation benefit

Growth stage 30 is also an ideal time to apply a plant growth regulator, such as trinexapac-ethyl or chlormequat, to manipulate plant growth, Mr Smith said.

The aim is to control apical dominance and help balance the flow of nutrients and energy across the leaves, stems and developing spikelets, giving the plant the best chance of retaining as many tillers as it can support, with strong stems and large ears.

There is an important distinction between this early growth ‘manipulation’ and the use of PGRs at the later GS 31/32 or 37/39 timings, where the focus is on growth ‘regulation’ by shortening and strengthening the stem to reduce lodging risks, he noted.

Nutritional boost

Supporting root development of more backward crops is another important consideration at T0, and phosphite-based biostimulants have been shown to boost root growth and tiller retention, as well as enhance PGR effects. Ideally, they need to be used early, typically at GS 30, although there may be some benefit up to GS 31.

Trace elements can be a useful addition to support healthy crop growth too, said Mr Smith, particularly where previous soil testing has highlighted potential deficiencies.

“Many growers might already include magnesium or manganese, but a number of Gold soil tests we’ve done have come back showing low levels of zinc and boron on several farms, so these may be worth including at T0 and T1 where necessary.”

This season, Mr Smith hopes to conduct a tramline trial comparison to see if there is any tangible benefit to crop growth, yield and grain quality from applying zinc and boron at T0 where issues have been highlighted by soil testing.

Timing is everything

Finally, Mr Howard advises growers to be open-minded about T0 spray timing.

“Typically, many wait for GS 30, but crops are sometimes beyond that by the time of application, and when catchy weather delays spraying, some may wait until the T1 and perhaps try combining the two.

“Having a gap between T0 and T1 is beneficial though, so be flexible with the early timing. If disease is present and you are 2-4 weeks out from T1, it is worth treating, subject to product label restrictions,” he said.

Many products can only be used from GS 30 onwards, but there are some that can be applied earlier, including biological controls, he concluded.

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