Focus on rust and septoria at T3

Cereal growers should focus on controlling septoria and rusts with T3 fungicide sprays, experts have advised.

Rain earlier in the season helped Septoria tritici spread up plants, particularly where weaker triazoles were used, rates were too low or T-timings were over-stretched, explained BASF’s cereal fungicide manager, Rosie Bryson.

“Disease is now clearly visible on leaf two and in some cases even on flag leaves. To add to the pressure the recent increase in air temperatures will further encourage its spread.

“In most situations wheat crops still have a lot of growing to do and they are going to need protection during what’s left of the season.”

Warm, dry weather is also likely to increase brown rust risk to susceptible varieties such as Cordiale, Alchemy and Istabraq, she noted.

Yellow rust is another threat to varieties like Consort and Robigus, but while it has been seen in sites in Scotland, Yorkshire and the eastern counties, the recent warm weather is likely to have reduced the risk in many areas, Dr Bryson added.

Syngenta’s Matt Pickard agreed that Septoria tritici and Septoria nodorum pressure has been increased by rain in May and recent warm, dry conditions are ideal for rusts.

He urges growers to keep ears and upper leaves clean of disease for the next six to seven weeks of grain filling to maximise yield and grain quality. Every extra day that crops are kept green can lift yield by 0.15-0.2t/ha and quality by 0.2kg/hl before harvest, he said.

“Across four seasons of trials, adding Amistar (azoxystrobin) to a triazole fungicide at T3 improved yield in almost 90% of cases. On average, the yield gain from adding 0.3 to 0.5 litres/ha of Amistar was 0.3t/ha. That could increase grower margin by over £10/ha.”

Dr Bryson suggests a T3 is likely to be important on most crops, especially milling wheats and recommends using epoxiconazole (Opus) for septoria and rusts and pyraclostrobin (Comet 200) for rust control.