Wheat growers should be cautious over early fungicide sprays

Wheat growers should be cautious about rushing in with early fungicide sprays to control septoria disease as there is little evidence to suggest these will be beneficial.

Growers should be examining crops for rust diseases which will respond to an early T0 spray in late March/early April, but treatments aimed at septoria are unlikely to see any yield response.

Jonathan Blake, fungicide expert at crop consultants Adas, said septoria is set to be a threat this season after a wet winter, with current cold weather having little effect on controlling the disease.

See also: How to keep wheat septoria at bay in a high-disease year

“There is little evidence to show that wheat growers will see anything beneficial in terms of septoria control from a T0 spray,” he told Farmers Weekly.

Mr Blake added that septoria, which thrives in wet conditions, continues to grow in wheat leaves even when leaves stop growing due to very low temperatures.

“Cold weather will have checked rusts, but it will not have slowed down the development of septoria,” he said.

Rust risk

A T0 spray should be used largely when rust is present in wheat crops or where a rust susceptible variety is grown, and then an azole, such as tebuconazole, or a strobilurin should be used.

jonathan blake

Jonathan Blake © David Jones

He added that one reason in favour of a T0 spray may be to give flexibility to fungicide programmes if a later T1 spray is delayed due to poor weather.

One the biggest mistakes growers make is to go too early with T1 sprays, when leaf three is fully emerged, so Mr Blake suggests holding back with any T0 spray into April if possible so as to keep the T0-T1 spray gap to about three weeks.

He believes with the decline in efficacy of the SDHI fungicides against septoria, growers need to rethink their programmes to maximise the effective life of this group of fungicides. Popular SDHI-azole products include Ascra, Aviator, Elatus, Adexar and Librax.

Two SDHIs

Growers should be asking themselves do they need two SDHIs, at T1 and again at T2, or can they just use one. The use of one SDHI at T2 is often a good policy when a variety with good septoria resistance is selected and then is drilled late.

In a three-year trial, Mr Blake looked at a range of varieties with different septoria resistances, covering the high disease year of 2014, the low disease year of 2015 and medium disease year of 2016.

“Over the three years there was no benefit from using two SDHIs on the most resistant varieties,” he said.

As septoria disease cycles relatively slowly, if the T1 was not powerful enough then an increased dose could be given at T2 for a some kickback effect.

Varietal resistance 

Mr Blake suggests when growing a variety with good resistance and late drilled, growers should be asking do they need an SDHI at all, as there was little yield benefit from adding a SDHI in his trials. He defined varieties with good resistance as those over scores of 6, such as Revelation.

There are still cases with heavy disease pressure when susceptible varieties are drilled early when there is a place for two SDHIs, but he adds that if growers are late sowing with a septoria resistant variety they can think about starting to cut back on fungicide costs.