With septoria active and moving up the plant, weather delays to winter wheat T0 sprays are a cause for concern.
High levels of septoria were visible in untreated winter wheat plots at Bayer’s Callow development site near Hereford this week, where time lapse cameras were being installed to provide as-it-happens images of crop and disease development for a third season.
The site received a T0 application of Bravo (chlorothalonil) + Folicur (tebuconazole) on March 31 but, given recent wet weather and ground conditions, the commercial wheat crop on the farm has yet to receive its spray, said Bayer technical manager Gareth Bubb.
Of concern were levels of disease across all varieties, even those with better rating for resistance to septoria.
“There is nearly as much brown leaf as green leaf in some of the untreated plots. Disease pressure remains high, even in the later-sown plots. Disease is active and moving up the plant. It has not been cold enough to slow the septoria down to any great extent; it will have had more of an impact on yellow rust and mildew, ” Mr Bubb said.
With changeable weather conditions around the country delaying T0 fungicide applications on many farms, there is a concern the spray timing may be missed, putting pressure on subsequent T1s.
And with the T1 timing fast approaching, some growers may be considering omitting the T0 spray.
“Even if you are getting close to a planned T1, I would still go with a T0,” said Mr Bubb, who suggested a cut-off point for a T0 of 10 days before a planned T1.
“I would still go at 10 days before. But if leaf 3 is more than 50 per cent emerged, then that is when you make the call, because then you are at the T1 timing; that is when you have got to use your septoria chemistry.
“Even if T0 is delayed, T1 has to be targeted at leaf 3 fully emerged.”
Prothioconazole + CTL (Proline+Bravo) would be as good an option at T1 as prothioconazole+bixafen+CTL (Aviator XPro+Bravo) at T1 “provided everything has gone right”, he added. If T0s are significantly delayed, or missed the SDHI approach would be the preferred option.
“With the amount of disease on this site I would be going with Aviator+CTL anyway, because of the septoria pressure,” Mr Bubb said.
View the time lapse images at www.bayercropscience.co.uk
Source: Bayer/G Bubb