AUTUMN-SOWN crops have been flying through the growth stages and flag leaves are emerging almost a month earlier than normal in some southern wheat crops.
Experts are warning that this has reinforced the importance of using regular field inspections and not calendar date to determine spray timings.
Leading agronomy firm, Hutchinsons, has picked up on several reports of leaf one emerging, with Gallant, Skyfall and Cordiale highlighted as three particularly forward varieties around the Wash, in parts of south Essex and some south of London. Growers in Scotland will not have experienced this yet, though crops are growing at an unprecedented rate.
The unusually advanced nature of some crops is in stark contrast to others elsewhere that are struggling to get going due to recent dry, but cool conditions. This will create considerable challenges for spring fungicide programmes, pointed out Hutchinson’s technical development director, Dr David Ellerton.
“There is a huge variation in growth stages of winter wheat across the UK, with many late-sown crops struggling in dry soils.
“The majority of crops are around GS 32 with leaf three emerged or emerging, but the most backward are still at GS 30-31. Some seem to have stopped growing altogether.”
While many of the most advanced wheats were sown early and thrived during a mild autumn and winter, some later-sown crops are also showing signs of early flag leaf emergence.
It is unclear whether the exceptional development is due to the relatively mild growing period so far, or a stress reaction triggered by dry conditions.
Growers with very advanced crops must be prepared to treat them as soon as the appropriate growth stage is reached, regardless of the calendar date, Dr Ellerton said.
“Flag leaf emergence in most crops will be around the usual timing of mid-May, but if it is out early, you’ve got to protect it.
“Even if septoria risk is currently relatively low in the dry, cool conditions, the situation can quickly change, as we saw in 2012 when we went from drought to deluge.”
“It’s not worth the risk of delaying. In this situation, missing the flag leaf timing will leave the most important leaves for yield production unprotected with huge implications for yield reductions.”
He recommended applying a mixed T2 spray based on the varied modes of action of a multi-site protectant, SDHI and triazole.
Where flag leaf sprays are applied early, he advised increasing the doses of multi-site and SDHI components to extend septoria protection as far as possible and bridge the gap through to harvest.
But whatever rate or product is used, spray intervals should still not exceed three to four weeks, he argued.
So early T2 application is likely to require an additional spray later in the programme to protect crops throughout the remaining growing period and avoid compromising yield.
“If crop growth slows down and extends the gap between flag leaf appearance and ear emergence, there may be a need for an interim spray between T2 and T3.
If not and crops remain forward, with ears also emerging early, these should be protected as normal with a T3 fungicide and then an additional spray considered three to four weeks later.
“Fungicides don’t offer the same curative ability that they once did, so it is essential crops are treated at the correct growth stage to avoid disease getting established,” he said.