Extra curative activity might be needed in wheat flag leaf fungicide sprays where growers made use of weather windows and applied T1s early, say agronomy experts.
“If you’ve hit leaf four rather than leaf three you will have no protection on leaf two, as it won’t be emerging at the time of application,” he said.
That left growers dependent on a well-timed flag leaf spray to cure any latent infection on leaf two, he said. “Any delay in application will mean the crop is more at risk from yield loss from disease infections. Under those circumstances, and a possible four to five-week gap, it is very possible growers will see septoria symptoms on leaf two or three around the time of the T2 spray.”
Early T1 sprays will need good T2 timing
Risk of septoria infection of leaf 2
Extra curative activity required
Persistence needed for extra green leaf area
In extreme cases where T1s had been applied before 15 April it might even be necessary to apply a low dose of triazole fungicide specifically as leaf two emerged to remove latent infections on leaf three, before spraying a flag leaf treatment as normal, he suggested. “It is better to use a small amount of triazole on leaf two and then hit the flag leaf timing than shift the whole thing forward and miss the key timing.”
Masstock agronomist Tim Horton said he had managed to delay most of his growers’ T1s until last week. “That’s looking like a good decision now.”
Where growers had gone early extra curative activity at T2 would help to increase kick-back against latent infections that could be in the leaves, but not showing symptoms, he said.
Prioritising susceptible varieties, or those where leaf three had definitely not emerged was also critical. “In Viscount, for example, leaf three wasn’t there as early as some other varieties, so potentially there could be an issue in that one.”
Open or backward crops would also need extra persistence from the T2 spray, he suggested. “In more open crops the lower leaves contribute more to yield, so you will want more persistence from your T1, but the T2s must also be persistent to prolong green leaf area all the way down the plant.”
Mixing the boscalid-containing product, Chord, with high azole-loaded fungicide Brutus was his preferred solution at flag leaf. A mix of 0.75-1 litres/ha of Chord plus 0.75 litres/ha Brutus gave a good dose of curative triazole plus more than enough boscalid to bring extra persistency and green leaf retention, he said.
That type of mix – Tracker replacing Chord at a similar dose – had worked effectively in an ADAS/BASF trial last season, Mr Blake said, giving over 1-1.5t/ha more yield than either Brutus (1.5 litres/ha) or Tracker (1.5 litres/ha) alone.
One knock on the mix has been the extra cost; at those doses it costs about £30-35/ha, according to Mr Horton, but he was confident that it would more than pay for itself. “We’ve been seeing yield responses that more than pay for the increased cost.”