The recent rain is increasing the septoria threat in winter wheat, as well as stretching spray intervals between sprays for some growers, according to agronomists.
Most reckoned very few flag leaf sprays had yet been applied because of poor weather, but were hoping growers would be able to apply sprays as soon as conditions improved. However, weather forecasts for the week did not look particularly promising.
“Probably less than 5% has been sprayed in the field so far,” Andrew Blazey, a Prime Agriculture agronomist in Essex, said on Monday [14 May].
With the gap between T1s and T2s now getting towards four weeks, ProCam’s David Ellerton was getting concerned by the enforced lack of activity. “We don’t like to stretch the gap beyond four weeks, and it looks as though we’re running into the same scenario as last year when we had some up to six weeks.”
Lincolnshire agronomist Sean Sparling was less concerned, despite a similar gap. “There is noticeable brown rust expression in the base of crops, and you can see fungicides still taking out yellow rust, but generally leaves one to three are clean.”
Septoria was now Mr Blazey’s primary disease concern. “It is there on leaves four and five.” Rain splash and wind rub could easily have infected upper leaves, he suggested.
Conditions had been conducive to septoria spread, Ruth East, an AICC member in Lincolnshire, agreed. “If it comes warm now it could be the next big problem.”
Its re-emergence as a threat meant growers would need to re-assess use of lower triazole doses of 25-40%, Mr Blazey warned. “I was recommending 60-70% triazole dose on rust varieties, such as Robigus and Alchemy, anyway, which should be adequate for septoria. On dirtier varieties, such as Brompton, Solstice and Malacca, it needs to be 75% plus.”
Provided sprays could be applied in the next week to 10 days, he thought it would be possible to get on top of disease with a triazole/chlorothalonil/strobilurin combination. “If it gets past that we might need to drop chlorothalonil out and add extra triazole on the dirtier varieties.”
Mr Starling said he would be adding some Corbel (fenpropimorph) to that combination. “A quarter of a litre will beef up rust control.” His dose of triazole would be a minimum 0.7 litres/ha of Opus (epoxiconazole) with Amistar Opti (azoxystrobin + chlorothalonil), he said.
Ms East was recommending Amistar (azoxystrobin) on second wheats because of its take-all activity, and Comet (pyraclostrobin) on first wheats as her strobilurin choices.
But Comet supplies were getting a bit tight, she noted. “These shortages are ridiculous. Either manufacturers are not making enough or distributors are not prepared to carry stock over.”