Early spray needed to keep yellow rust at bay

Giles Benson was prompted into an ultra-early fungicide spray this spring to keep yellow rust out of his promising-looking winter wheat crops.


A so-called T-minus 1 (T-1) spray was applied for the first time this season on his south Northamptonshire arable unit on yellow rust susceptible wheat varieties.


The mild winter and a quickly drying early spring has seen yellow rust outbreaks in the East, so Mr Benson was willing to try out this new timing.


See also: Spray timing critical in battle against septoria


“The early treatment buys one time, and stops rust exploding before we can get on with our normal T0 spray,” he says.


The fungicide treatment was used on rust-susceptible varieties such as Viscount, Solstice and Robigus, whereas newer more resistant varieties Crusoe and Leeds were not sprayed.


“If we let disease get into the crop, we will be fighting it all the season,” he says, adding that this could see him moving to a five-spray fungicide season this year rather than a more normal four.


Mr Benson’s agronomist Bill Barr of crop consultants Prime Agriculture says he is seeing yellow rust on most wheat varieties throughout Northamptonshire and Bedfordshire.


Agronomists Bill Bar, Giles Benson and Nick Myers


Above, left to right: Bill Barr, Giles Benson and Nick Myers examine a crop of Solstice winter wheat that had an early fungicide spray.


“The level of yellow rust is much more than normal and we need to get on early and get the fungicide down into the canopy,” he says.


The product choice was between two fast-acting triazoles tebuconazole and cyproconazole for rust control, and the former was chosen at a reduced rate.


This early T-1 was applied in late February and early March at a relatively low cost of about £5/ha, and yellow rust was difficult to find in late March.


The triazole was used without chlorothalonil as it was deemed too early to use this protectant fungicide against septoria as the key top three leaves were not yet visible.


“You are never going to eradicate septoria that early in the season, so a T-1 should be aimed at rust control,” says Ben Freer, an ex-NIAB agronomist who has recently moved to BASF.


Mr Benson manages about 1,400ha of arable land split equally between winter wheat and oilseed rape, with 70ha of spring barley planned this year in bad blackgrass fields.


The Turneys Farming operation covers two arable blocks – one at West Hall Farm, Quinton, four miles south of Northampton and the other 10 miles south-west near Silverstone motor racing circuit, with soils ranging from heavy blue clays to limestone brashes.


Wheat yields average 9t/ha and this season’s crops were drilled between mid-September and mid-October, emerged strongly and grew well in the generally mild weather.


The approach to a T0 spray, likely to be applied in the last few days of March, will depend on whether crops have received an earlier T-1, with a spray cost likely to be £7.50-10/ha.


For those wheats with an early spray, the T0 is likely to be a conventional triazole-chlorothalonil mix, such as a pre-formulated cyproconazole-propiconazole-chorothalonil product, says Mr Barr.


Crops without an early T-1 spray, will get the triazole tebuconazole with the addition of chlorothalonil, plus a strobilurin product to boost overall rust control.


ACTIVES


Popular strobilurins



  • Amistar – azoxystrobin

  • Comet – pyraclostrobin

  • Galileo – picoxystrobin

  • Swift – trifloxystrobin


Fandango and Firefly contain the strobilurin fluoxastrobin and triazole prothioconazole


Major new-generation SDHI products



  • Seguris – SDHI isopyrazam + triazole epoxiconazole

  • Adexar – SDHI fluxapyroxad + triazole epoxiconazole

  • Aviator – SDHI bixafen + triazole prothioconazole

  • Vertisan – SDHI penthiopyrad


    Older SDHIs



    • Tracker – SDHI boscalid + triazole epoxiconazole



      • Strobilurins were introduced in the late 1990s, but heavy use led to septoria strains becoming resistant to these fungicides and strobs are now largely used for control of rust diseases.


        Nick Myers, head of crop production at distributor ProCam, believes these strobs do have a place in a T0 treatment for second wheats to reduce take-all if the application is washed into the roots by subsequent rain.


        Mr Freer adds that a T0 treatment rarely gives a big yield response but it will give a sizeable response if the following T1 spray is delayed.


        Choice of a T1 spray will be based on the need for eyespot control, good rust control, products that can be mixed with chlorothalonil and the awareness that the new SDHIs will give a useful yield response, says Mr Barr.


        For eyespot-susceptible varieties or where the disease is prevalent, then the T1 will be based on the older SDHI boscalid or the triazole prothioconazole.


        In this case, boscalid plus a good rust active triazole, such as epoxiconazole, and adding chlorothalonil and possibly a strob could be the mixture of choice.


        If eyespot is not seen as a key problem then a triazole-chlorothalonil mix, or a new SDHI approach, is likely and currently little eyespot has been seen on the farm.


        The cost of the T1 is likely to rise sharply to about £35-40/ha at this key fungicide timing for disease control.


        “You are now looking to protect the upper leaves, so the spend will start to go up,” says Mr Freer.


        The early control could pay dividends as treatments could be cut later if it turns out to be a low disease year.


        “If you go on with a robust T0 and T1 then you can play it more by ear for T2 and T3,” says Mr Myers.


        A T2 treatment at the flag leaf stage in May is likely to be based around the new generation of SDHI-triazole products with a typical spend of £33-40/ha, similar to the T1 treatment cost, with an eye on adding extra rust activity depending on which triazole is used in the mix.


        “We would be focused on green leaf retention so will be looking at a SDHI-triazole approach and would not plan to use a strob unless it turns out to be a bad rust year,” says Mr Barr.


        The rust disease threat nationwide has been complication by the emergence of the more virulent Warrior race, while the resistance of some varieties to the disease – such as Oakley – has broken down.


        “We don’t have rust-proof varieties so there may be a need to add a strob in at T2,” says Mr Freer.


        A T3 ear spray is set to be based around prothioconazole, primarily against fusarium, but there may be a need for another triazole or strob to boost control of late-emerging brown rust.


        Mr Myers favours a prothioconazole/tebuconazole approach, while Mr Freer says there could be a scope for a strob to boost rust control.


        This would probably put annual fungicide spend at about the £100/ha mark compared with £89/ha in the low-disease year of 2013 and £108/ha in the high-disease year of 2012, which Mr Benson admits was probably not enough.


        Each variety has a planned fungicide budget, but Mr Benson insists: “We will not stop spending when the budget is reached.”


        The overall approach relies on mixing modes of action to prevent resistance building up with triazoles, SDHIs, strobs and multisite protectants such as chlorothalonil all considered.


        Fungicide experts at crop scientists group ADAS says the strobs still have a useful part to play in a fungicide programme but are not essential partners.


        In wheat, they have good activity on rusts and are particularly useful when a triazole partner has less activity on rusts, they add.


        “They can be a valuable tool to give a boost to yellow and brown rust control especially at the T1 and T2 timings,” says Mr Barr.