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30 Jun 2021

Robust resistance and yield potential impress

As featured in Arable Farming Magazine

Robust resistance and yield potential impress

by Arable Farming

With disease resistance an increasingly important driver for growers when choosing wheat varieties, we talk to two farmers who appreciate the flexibility and high yields varieties are now offering, and find out what fungicide strategies they are using.

Despite being in a disease hotspot just five miles from the Wash, Lincolnshire grower Mark Tinsley was able to adopt a fairly relaxed fungicide approach on his wheats earlier this season, before bringing in newer chemistry ahead of the flag leaf timing.

No wheats received a T0 due to dry weather, while T1 applications were tailored to potential disease problems with an eye on the wet forecast.

Mr Tinsley is growing RGT Saki for seed for the second year running.

Taking account of the varietys robust septoria rating and its high rust scores, 0.75 litres per hectare of Wolverine (fluxapyroxad + metconazole) was deemed sufficient at T1, just under 40% of the full rate, costing about £21/ha.

KWS Firefly grown as a commercial Group 3 received a two-thirds rate (0.8 litres/ ha) of Aviator (bixafen + prothioconazole) and a one-third rate (0.

2 litres/ha) of Toledo (tebuconazole) to take account of its weaker rust ratings, costing about £30/ha.

Skyfall for seed was treated with a three-quarter rate of Elatus Era (benzovindiflupyr + prothioconazole), mainly to keep yellow rust at bay, which cost £35/ha.

The approach has worked well.

Mr Tinsley says: Wheats came through to T2 looking pretty clean, particularly the RGT Saki.

While I wouldnt say there was no septoria in the base, the variety has a 6.5 resistance rating and in our experience is probably better than that. While it was something to be aware of, we werent worried too much.

All wheats looked very well approaching T2, so he opted for Revystar (fluxapyroxad + mefentrifluconazole) at the recommended rate of one litre/ ha across all varieties.

Last season, Octobersown RGT Saki after potatoes yielded 11.5 tonnes/ha and a November-sown crop after beet did 11.6t/ha.

The variety was our best performer it was grown from basic seed sown at 150- 175kg/ha.

It is at the top end when it comes to vigour it seems to tiller out very well and looks to be very competitive.

Even so, to produce a yield like that in the year we had was quite extraordinary, even on our fertile ground.

Im hoping this seasons crop will do as well or better.

It was drilled in mid-October after potatoes at 160kg/ha.

Theres a fair bit of fertility behind it, so although its a pretty stiff-strawed variety we applied a comprehensive PGR programme and limited nitrogen to 200kg/ha.

Weve had enough rain now to see it through the framework is there for a very good crop, he adds.

In the field J.W. Pitts and Sons, Mears Ashby, Northamptonshire

Omitting both the T0 and T1 fungicide sprays and applying a pared-back T2 may seem too much of a risk for many wheat growers, but for Andrew Pitts it makes perfect sense this season for his crop of RGT Saki.

Thanks to a dry March and even drier April no disease has been seen on the crop.

Although May saw plenty of rain and the crop was full of promise, Mr Pitts put his faith in RGT Sakis strong disease resistance scores when it came to the flag leaf application.

He says: Leaf 3 remains clean and Im told there is very little disease out there. I applied one litre per hectare of Ascra (bixafen + fluopyram + prothioconazole), due to the recent rain.

KWS Extase, another robust variety but with a lower AHDB Recommended List treated yield figure, received a similar programme.

I cant see the point of growing varieties with good disease resistance without making full use of that genetic capability.

Had we not had rain I would have gone with something cheaper and older, such as Aviator, Mr Pitts adds.

Other varieties, such as RGT Gravity and Skyfall, had tebuconazole and pyraclostrobin at T0, followed by Adexar (epoxiconazole + fluxapyroxad) at T1, both aimed at yellow rust and to keep the lid on septoria.

At T2, these varieties received fluxapyroxad and mefentrifluconazole at one litre/ ha to combat latent septoria, plus pyraclostrobin to maintain rust control.

All seed crops will be treated with prothioconazole at T3 to protect against fusarium, the dose dependent on the weather at flowering.

Thanks to the recent rain, RGT Sakis early promise has been borne out, says Mr Pitts.

It was sown in mid-October and tillered well, looking very vigorous in autumn, but only needing moderate growth regulator in spring.

It looks set for a good harvest.

Evolving It has been an incredibly cheap variety to grow and I expect to have a lot more next year.

Varieties that can look after themselves and also yield well are becoming key triazoles are becoming less effective and septoria will always be out there and yellow rust is continually evolving.

In addition, good disease resistance means you can prioritise more susceptible wheats, especially useful in a tricky season when applications might be delayed. That said, we have pretty good sprayer capacity and can get round our susceptible varieties in a couple of days, but it is still good to know we have varieties that help spread the risk.

In recent years, plant breeders have overcome the significant yield penalty associated with high septoria resistance.

Dr Cathy Hooper, RAGT Seeds technical sales manager, says: There are now several examples of very high yielding wheats with excellent septoria resistance on the Recommended List.

RGT Saki has an outstanding treated yield, rated at 104% of controls on the Recommended List, and in 2020 it out-yielded all other wheats in official trials, Dr Hooper adds.

In addition, RGT Sakis excellent untreated yield of 85% reflects its strong disease resistance scores 6.5 for septoriatritici, 8 for yellow rust and 7 for brown rust.

RGT Saki will respond when pushed hard, but will also help protect yields when fungicide application is delayed or rates trimmed.

The most risk-averse growers will continue to use robust fungicide products and doses, says Dr Hooper.

This does offer best protection to both fungicide and plant genetics, but at a cost.

Others will cut rates as much as possible to minimise expenditure, which can leave chemistry and genetics more exposed to resistance.

We think the best approach is to view a variety like RGT Saki as another tank-mix partner, using appropriate rates of suitable chemistry at the correct timings according to disease risk.

This should enable some flexibility depending on the season, although vigilance remains key.

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