Wheat grower tackles septoria fungicide resistance

Wheat’s biggest disease threat septoria and this disease’s resistance to fungicides are the major challenges for Hertfordshire grower Andrew Watts, who harvests more than 1,000ha for milling wheat outlets.

He is using crop rotations, varietal choice and drilling dates to keep the yield-sapping disease at bay, together with a cost-effective fungicide strategy aim at preventing resistance build-up.

Even though azole fungicide effectiveness has declined and the first signs of resistance have been detected with the key SDHI fungicides, he is trying to keep on top of septoria with a wide mix of products.

“The efficacy of current active ingredients has declined and will continue to lessen, so we have to look beyond the can, while at the same time devising a cost-effective fungicide strategy,” he says.

See also: Yellow rust as serious as septoria for wheat growers

Andrew Watts in a field

Andrew Watts

Non-fungicide methods of septoria control such as choosing more resistant varieties are taking on greater importance than a decade ago, but so is a well-constructed fungicide programme.

Mr Watts has devised a fungicide strategy using just one SDHI, along with azoles and strobilurins and the multisite protectant product chlorothalonil to help limit fungicide resistance.

Mr Watts manages a large track of mainly arable land from a base at Mentley Farm, five miles north of Ware, east Hertfordshire, on a range of soils, from chalk through to gravel and strong clays.

Key wheat varieties grown are the breadmaker Crusoe, biscuit-maker Monterey and feed wheat Diego, which goes for blending at local mills rather than to the animal feed market.

His 1,100ha of wheat is grown alongside other winter crops such as barley, oats, beans and oilseed rape with spring breaks of barley and peas, and wheat yields averaged 9-10t/ha last season with some crop hitting 12t/ha.

“We look to keep the wheat leaves clean of disease and our aim is to get after septoria early,” says the former chairman of the NFU combinable crops board.

Expert view

Metconazole used to be the third-best azole for septoria after leading azoles prothioconazole and epoxiconazole, says Jonathan Blake, fungicide expert at crop consultants Adas.

But the gap between the azoles has narrowed and a mix of metconazole with the SDHI fluxapryoxad (Librax) is as effective as the same SDHI with epoxiconazole (Adexar) at the same dose rate against septoria.

This is likely to be due to the two molecules working well together making Librax at least as effect as Adexar at the same dose rate on septoria.

However, metconazole is not as active as epoxiconazole on yellow and brown rusts, so if rusts are a problem, the epoxiconazole component would become more important.

His first T0 fungicide in March is based on chlorothalonil, adding an azole such as cyproconazole if needed for rust control.

A later T1 April spray is based on an azole such as epoxiconazole with the addition of a strobilurin and also chlorothalonil, but with no SDHI.

Strobilurin achieves greening effect

The strobilurin is used for its greening effect on the crop and also to give added rust control, whereas he is trying to limit SDHI use to protect their future efficacy against septoria.

For his T2 flag leaf spray in May he plumbs for an SDHI-azole mix, and last season switched to BASF’s Librax rather than the company’s Adexar, which he had used the previous season.

Librax uses the same fluxapyroxad SDHI as in Adexar, but has the azole metconazole rather than the more popular epoxiconazole.

By using a different azole, Mr Watts is hoping to reduce selection pressure and hence slow down the build-up of resistance.

“We looked for the most cost-effective treatment that gave value for money and might help with resistance management,” he says.

For the T3 head spray, he is keen to protect grain quality and opts for an azole such as prothioconazole alone or mixed with tebuconazole for protection against ear diseases such as fusarium.

“Late summer rains can be the sting in the tail, so we need to protect the crop from late disease, especially as all the crops are going for human consumption,” he says.

Keeping crops green and not stressed by disease is key in the summer, when some of his lighter-land crops can come under stress on his lighter drought-prone land.

“We grow the varieties the local consumer wants with a range of maturity dates and then we need to protect all that potential with a good fungicide regime,” he says.