The dilemma over how long to leave the gap between T1 and T2 fungicide applications is taxing our Crop Watch agronomists.
David Martindale of Arable Alliance in Yorkshire says that with flag leaves now emerging on earlier crops, the dilemma is how long to leave the gap between T1 and T2 fungicides.
“With Septoria tritici pressure high and nearly half of the grain yield obtained from the flag leaf alone, the T2 timings should not be delayed much past the normal timing.”
In the East, most wheat crops are now at GS32/33 and the flag leaf will emerge within two weeks, says Philip Vickers of Farmacy. T2 timings are now being planned and will need to be robust, as the threat of septoria is great.
“The SDHI group of chemicals with a septoria-active triazole or a large loading of triazoles (at least two septoria-active triazoles) will be the backbone of any treatment.”
Looking further ahead, he says: “We need to be thinking about fusarium risk if the wet season prevails. Varieties such as Gallant and Grafton are particularly susceptible, according to the HGCA Recommended List.
“Prothioconazole and an SDHI at T2, followed by prothioconazole, tebuconazole and metconazole mix at T3, could be appropriate.”
However, in the South, AICC agronomist Tod Hunnisett believes the risk this year is that the gaps between fungicide applications will be stretched beyond their three to four-week optimum (depending on the rates and products used).
“If this does happen, an addition of triazole to top up the outstanding recommendations might be worthwhile.”
Delayed applications have also been a concern with barley, Mr Martindale says. “Some winter barley crops have also had late T1 fungicide applications, allowing diseases such as rhynchosporium to spread higher up the canopy. T2 fungicides will be required when the awns are showing to keep on top of rhynchosporium and provide further brown rust control.”
With oilseed rape, the concern is lodging. “Oilseed rape crops have been knocked around with the storms,” says Mr Martindale. “This has caused some severe leaning in some crops.
“Most have sprung back up again, but the stem bases could have been weakened, which could lead to some lodging issues when the crop canopies become a lot heavier towards harvest.”
Neil Donkin adds that while oilseed rape crops should have had a fungicide at early petal fall, if that is now more than three weeks ago, a follow-up treatment should be applied to see the crop through to harvest.
“So far this year, weevil numbers are low, so there should be no need for insecticides at this stage.”