Fungicide sprays at the T2 timing are being strengthened and spray intervals shortened as brown rust continues to cause concern, after the disease infected crops much earlier than expected this season.

A mild winter, stressed crops and either delayed or poor T1 applications are believed to have contributed to the current situation. In fact, many susceptible varieties have already received an extra T1.5 fungicide spray to halt the disease.

This is adding to the cost, complexity and frequency of fungicide programmes, in a season where crop potential is likely to have been compromised by the wet weather and most growers are keen to keep a lid on expenditure.

See also: What the mancozeb withdrawal date means for potato growers

Variety effects

The Group 1 wheat Crusoe is having a particularly bad year, report agronomists, who acknowledge its brown rust rating of 3 and susceptibility to the disease.

However, they point out that it is very unusual to find brown rust in the variety before T1.

“What we’re seeing in Crusoe this year is not normal,” says Dick Neale, technical manager at Hutchinsons.

“Once the disease is established and it’s warm enough, it can cycle in four to five days, which is why there can be a need to keep going back through the crop.”

Other varieties, including Champion and Cranium, are also affected, with the Recommended List ratings being a good indication of their vulnerability, he notes.

“It tends to sit in the bottom of crops, so getting the spray right down into the canopy helps.”

T2 additions

If it is not too late, including either tebuconazole or a strobilurin such as azoxystrobin or pyraclostrobin are options for rapid knockdown at T2, explains Dick.

He stresses that restrictions on the number of applications and label conditions must be adhered to.

“Remember that you are only allowed to use two strobilurins in a season and check the label of your chosen tebuconazole product, as the maximum dose varies and some can only be applied once between GS 30 and 40,” he says.

He accepts this will increase costs. “Where you do need to boost your chosen T2 product, it might add another £5-£10/ha.” 

Temperature driven

Alice Andrews of Ceres Rural does not believe there has been a race change or a breakdown in varietal resistance to brown rust, but is concerned by how much earlier she was able to find the disease in the spring.

“It’s unheard of to find it pre-T1 and the weather didn’t seem to be that conducive to its development,” she says. “We know it’s temperature driven, but normally warm and dry conditions favour it.” 

In contrast, septoria is at more normal levels, she continues, and given the expanding choice of fungicide products offering good control of the disease, the disease is less of a concern.

Alice adds that Crusoe is usually a low maintenance variety until T2, when it gets a suitable spray aimed at its brown rust weakness.

“This year, it’s been forcing my hand,” she says.

“A hefty T1 based on Ascra [bixafen, fluopyram + prothioconazole] plus tebuconazole has given just two weeks activity in some instances. “We’ve had to get some tebuconazole or azoxystrobin on since then,” she reports.

Mind the gap

Her advice is to keep spray intervals tight and to correct any nutritional deficiencies.

“Add in something to boost rust protection if you’re using Revystar [fluxapyroxad + mefentrifluconazole], Univoq [fenpicoxamid + prothioconazole] or Miravis Plus [pydiflumetofen] at T2 and are growing a susceptible variety.

“Remember to check the label of your chosen tebuconazole product as we’ve still got T3 to come.”

Fortunately, varieties being grown to de-risk rotations, such as Typhoon and Palladium, are spotless, adds Alice.

Slipped timings

In the West, Ben Knight of Agrovista reports an abnormally high year for rust pressure – including crown rust on oats.

“Some of the T1 timings slipped a bit, which may have contributed to the situation,” he says. “We’re also seeing much more yellow rust than we normally do and septoria has been present all year.”

The majority of his T2 recommendations are based on Univoq, following the use of new arrival Iblon (isoflucypram) plus prothioconazoe/tebuconazole/spiroxamine at T1.

“We will try some of the new Adepidyn [pydiflumetofen] based material at T2 too, but it comes with a higher price tag.”

Case study: Craig Livingstone, Lockerley Estate, Hampshire

At the Lockerley Estate in Hampshire, a three-way blend of Extase, Siskin and Dawsum is remaining very clean and has not received any fungicides to date, reports farm manager Craig Livingstone.

“It wasn’t drilled until early January, which will have helped,” he says.

Craig Livingstone © Hugh Nutt

The opposite is true of his Crusoe, which has needed an additional T1.5 spray to keep on top of brown rust.

He is following that up with either Elatus Era (benzovindiflupyr + prothioconazole) or Revystar (fluxapyroxad + mefentrifluconazole) at T2.

“It didn’t get a T0 and the T1 was based on Ascra [bixafen, fluopyram + prothioconazole], so we’re reacting to the season.”

Craig usually spends around £85-£90/ha on fungicides.