The need for a T4 spray was being discussed by agronomists and growers at the Cereals 2024 event, as crops continue to come under pressure from disease.

With brown rust constantly cycling and septoria proving difficult to control – even where the best fungicides have been used – the application of a T4 to maintain green leaf and prevent disease from getting onto the ear was not being ruled out.

See also: Cereals 2024: Smart trap alerts OSR growers to pest threats

In an exceptional year, the main query was whether another application would provide value for money, with an approximate cost of £12-£15/ha being mentioned.

“People are sick of spraying,” said independent agronomist Jock Willmott of Ceres Rural.

“But brown rust is being really stubborn and behaving uncharacteristically, with tebuconazole failing to dry it up as we expected.”

Early drilled, thick crops are where all the issues are and brown rust has been present since the T1 timing, he added.

“Considerable effort has gone into spray volumes, accuracy and timing, but we are still seeing difficulties and the chemistry hasn’t worked,” he said.

Septoria 

Septoria has also been a challenge, with rate and product choice having mattered.

“It’s put the best materials – Adepidyn and Univoq – to the test, and the concern is that if this unsettled weather continues, we will see more disease,” said Jock.

Three weeks activity on disease has been the absolute maximum in such a testing year, he added.

“If you do need to spray again, remember the limits of two strobilurins and two SDHIs in one season, as well as the label rates of tebuconazole. For septoria, prothioconazole is another option.” 

In Dorset, septoria has been grower Bob Rowe’s main challenge, but he has also seen ramularia coming into his winter barley.

As a result, he is trying Miravis Plus on 30ha of his barley crop and is contemplating a triazole/strobilurin T4 to top up septoria control on wheat.

“Whether this is the new normal for septoria as climate change makes its presence felt remains to be seen,” he said.

“We’ve had huge amounts of rain and plenty of infection events, so we’ve had to spend on disease control and be really vigilant.”

Niab senior specialist in plant pathology Dr Aoife O’Driscoll agreed that it had been near-impossible to catch brown rust this year, with the disease recycling very quickly.

“It tends to pool in the leaf axils and sprays don’t reach that far.

“It has swamped the varieties in our plots here at Cereals and has given on-farm problems on a far wider basis than we are used to.”

Timing

As far as a T4 spray is concerned, the timing would be the last week of June and product choice will depend on what’s already been applied, she noted.

“If septoria is your biggest concern and it’s not on the flag leaves, there’s no need to go again,” she said.

The milling wheat premium is high enough to cover the cost of a T4, most agronomists suggested, with Group 1 Crusoe being particularly challenging to manage.

As Nufol is still to be applied, there must be enough green leaf left for it to be used and milling specification achieved.

“If you’ve come this far, the cost of a T4 can be justified,” said one agronomist.

“But it may not be what growers want to hear – some crops have already had five fungicide sprays.”