With sprayers poised to make their first key fungicide pass through winter wheat crops, Martin Rickatson seeks some advice from Agrii on planning and prioritising this season’s disease control demands.
Despite an improved disease resistance profile across the varieties making up this season’s national winter wheat crop, clear yellow rust risks and widespread cases of high early levels of septoria mean a T0 spray will be an essential fungicide programme foundation for most farms, while spot-on T1 and T2 timing will be crucial.
That is the advice for maximising yield potential from Jim Carswell, northern research and development manager for Agrii. While, like any other season, this one has its individual characteristics, wheat growers need only recall recent history, he suggests, to help them form a basis for this season’s strategy.
“While 2013 was a relatively ‘quiet’ disease year, 2014 was more akin to 2012, being an extremely challenging disease season, with many wheat growers experiencing the highest septoria pressure since 1990,” he says.
“At the same time, rusts lurked in crops at varying levels throughout the season. The value of robust fungicide and PGR programmes was evident in the four-tonne/hectare average yield bonus we saw in our variety trials across all regions.
“Overall the season is shaping-up to be more like 2013/14 and 2011/12 than 2012/13, and while it may have been a bit colder this January than last, early season conditions have been ideal for disease development in warm, wet and thick canopies.
There is a set of key factors which influence the septoria pressure any particular year’s crop is likely to face, says Mr Carswell, and their prevalence, and dominance should guide disease control programme development.
“The first ‘influencer’ is crop risk, according to the areas of highly susceptible varieties drilled nationally. While this year there is a better spread of varieties with varying levels of resistance and susceptibility, 45 per cent of the varieties we have sold have septoria tritici ratings of 5.5 or less, while 37 per cent have brown rust ratings of less than 6.
“Sixteen per cent have yellow rust ratings lower than 6, and it is also important to remember the Warrior race has a two-day shorter interval between infection and sporulation. The narrowness of the genetic base is concerning, and if two varieties you grow are both weak on yellow rust, you will stand a better chance of getting good control and avoiding spread where one or both are from diversification group one.” (See table).
The use of seed treatments of insufficient robustness gives cause for concern, adds Mr Carswell, with previous Agrii trials showing 0.43t/ha (0.17t/acre) average gains across Torch, Oakley and KWS Solo from the foliar disease benefits of fluquinconazole.
“But earliness of drilling is a key influence, and enhanced by mild winter conditions tends to create lush, disease-susceptible early growth. In 2013-14 trials we conducted with Crusoe, Horatio, Dickens and KWS Santiago, we saw septoria infection levels halved where drilling had been held back from September 11 to October 30, with early drilling challenging even the most robust fungicide regimes on susceptible varieties.
“On more susceptible varieties drilled early, even robust fungicide regimes struggled, while those same varieties had been sown later, they still required robust programmes. Generally speaking, drilling was pushed back a bit in autumn 2014, but early season October-
December conditions were ideal for disease development.”
The next influence is a conducive climate, he says, and while there was some cold weather in January, September to December mean temperatures were more like those of 2013-14 and 2011-12 than 2012-13, at an mean average of 9.3degC. The same period also saw 13.2 days of air frost, slightly more than in 2013 but still almost seven fewer than in 2012.
“Combined with ineffective fungicide spraying caused by insufficiently effective chemistry and/or lack of spray days, these are the factors which determine how challenging a year is likely to be in disease control terms.”
Monitoring of wheat variety tussock trials which form part of Agrii’s National Cereal Disease Survey is another useful guide, says Mr Carswell. Providing data which complements the UK Cereals Pathogen Virulence Survey for yellow rust, this comprises 39 wheat variety tussocks at nine national locations – eight in England and one at Drem, east of Edinburgh – which provide real-time monitoring of key wheat diseases, and identification of risk levels by location and variety.
“Early disease assessments at several key sites showed 80 per cent of varieties with yellow rust at Drem in late-November, with 23 per cent still infected in late-January.
“But no yellow rust was found in January assessments of tussock trials at our Wiltshire, Kent, Cambridgeshire or south Wales sites, while only one variety was infected at the Bishop Burton site in Yorkshire. At that same site, though, 83 per cent of varieties were showing significant septoria infection in early January, while levels were low at Drem and at the Kent and Lincolnshire sites, and no significant septoria was evident in south Wales, Cambridgeshire or Shropshire.”
Some 61 per cent of varieties at Bishop Burton were showing significant powdery mildew in early January, says Mr Carswell, while levels were relatively high at Drem and moderate in Cambridgeshire and Kent, and none was recorded in south Wales or Shropshire.
Recent Agrii trials back suggestions of a possible shift in triazole efficacy, with the best stacked triazoles appearing to pull away from single actives. Mr Carswell suggests this needs to be considered in relation to the identification last year by Rothamsted Research of new azole-resistant septoria tritici isolates of increased complexity, many showing ‘stacked’ gene mutations.
But triazoles remain essential for broader fungicide resistance management, helping to protect SDHI efficacy while still providing their own septoria, rusts and eyespot control benefits, and should still provide the basis on which to build this season’s fungicide programme, says Colin Lloyd, Agrii head of agronomy. Stacking is key to making the most from them, he says.
“In order to protect their efficacy for the longer term, they need to be used as the building block of a programme which goes on to include SDHI, multi-site, strobilurin and morpholine elements.
“Stacked triazoles are pulling further away from straights in septoria control and yield, and our trials show them now giving 0.8t/ha more than epoxiconazole alone. T0 triazoles should be chosen bearing in mind both selection pressure on septoria strains and the significance of other disease issues such as yellow rust and microdochium.
“In 15 years of trials we have seen an average 0.38t/ha response from T0 use, and in 2012 and 2014 the response was particularly high, at 0.75t/ha. But whatever the year and response level, the investment has always proven cost-effective.”
Making the best possible use of a T0 also guards against the risk of the T1 application being delayed, he says.
“Our trials suggest a 0.37t/ha yield penalty if the weather puts it back by a couple of weeks, with a 0.43t/ha benefit where T1 and T2 are delayed yet a T0 has been applied.
“Follow up with robust T1 and T2 regimes, matching chemistry to crop risk and disease threat, using a base of stacked triazoles with a multi-site protectant. Mixing azoles keeps septoria ‘guessing’, so switching at each timing seems sensible. Use the most active SDHIs, and consider strobilurins where rust is a threat.”
|Diversification group variety A|
|Diversification group variety B||DG2a||Low||Moderate||High|