Value in varietal resistance despite drought
24th August 2020
The importance of winter wheat variety disease resilience was evident at Bayer’s virtual Long Sutton demo, with physiological yield-benefits from fungicides also likely.
In the spring, picking Barrell and Extase apart wasn’t easy for site manager Darren Adkins – despite the near four-point gap in septoria ratings. That was true of most untreated plots, apart from the odd bit of yellow rust in Gleam, Kinetic, Saki and Spotlight.
But disease symptoms started to express themselves during the harvest run in and, by late June, differences in Barrel and Extase plots were clearly visible.
“Despite rainfall levels being much lower than the average, unprotected Barrel plots had septoria in the upper canopy. There was also some disease in Extase, but it didn’t really spread to the key yield-generating leaves.”
Green and clean
All fungicide-treated plots remained green regardless of septoria or yellow rust rating, but those with better septoria resistance were particularly clean.
That poses a question about the level of fungicide investment needed in low pressure situations.
But Mr Adkins is wary of growers gambling too heavily. “Last season we saw Extase deliver yield responses of over 1t/ha. Until June we had seen little in the way of septoria, and although disease control was clearly a factor, I expect the physiological crop benefits of Ascra (prothioconazole + bixafen + fluopyram) played a part.”
With yield data still to be verified, he is not sure how great any responses will be this season. But he does expect a bene t from fungicide programmes – even in Extase, which is expected to dominate wheat variety choices this autumn.
“Untreated Extase plots carried some septoria, and brown rust established on the top two leaves.
Again, I suspect we will see some greening benefit from the use of Aviator (prothioconazole + bixafen) and Ascra in the programme. Extase is an early maturing variety so prolonging green leaf area is useful.”
He feels the big gain from variety resilience is the farm flexibility it delivers. With the decline in curative fungicide activity, timing is more important than ever. Resilient varieties allow farmers to plan spray rosters by variety susceptibility, with some timing leeway if the weather is catchy.
Another gain is the appropriate use of chemistry. “If genetics are limiting the speed of disease development in the leaf, it is maintaining the preventative phase. It is where we use fungicides curatively that we put them under the highest pressure. What we have is genetics protecting the chemistry, and vice versa.
“It also allows fungicides to be targeted by risk. With the dry weather from March to May we applied two fungicide programmes to compare fungicide inputs in a low septoria pressure situation, using different rates of Aviator and Ascra.
“Both programmes began with a low dose of Savanna (tebuconazole) at the T0. The lower input programme followed with 0.8-litres/ ha Aviator + 1.0-litres/ha Folpet at the T1 and a T2 of 1.0-litres/ha Ascra + 1.0-litres/ha Folpet. With the higher input programme the rates of Aviator and Ascra were increased to 1.0- and 1.2-litres/ha respectively, the rate of Folpet remaining at 1.0-litres/ha.”
Based on previous seasons, Mr Adkins anticipates the combination of disease control and physiological benefits will make positive responses likely. What will be interesting is any corresponding yield increase associated with the higher rates applied at the T1 and T2 timings.
“We are undertaking a lot of research into improved disease diagnosis and more targeted use of fungicides. We might gain further insight through these Long Sutton trials.”
Covid-19 may have stopped growers gauging winter wheat yield potential on the rich, fertile soils at Long Sutton for themselves, but host farmer David Hoyles of G H Hoyles Ltd was happy to give Farmers Guide a snapshot of the varieties that impressed him.
A consistent YEN top performer, his Wisbech alluvial Grade 1 silt makes 12t/ha+ possible with sufficient sunlight through grain ll. He favours earlier maturing, high-yielding varieties, but also looks for good septoria and fusarium resistance, with North Sea frets a common occurrence.
Monitoring the plots throughout the season, KWS Parkin, LG Astronomer and LG Illuminate have all caught his eye. At 102 per cent of controls, KWS Parkin has the yield potential, and matures earlier than any on the list. He expects it to perform well in his fertile soils, but it is a little light against septoria, where LG Astronomer and LG Illuminate are both rated at 7. “Both LG Illuminate and LG Astronomer look like they have the potential for biscuit premiums.
“I’d probably opt for Illuminate as it has better specific weight, and LG Astronomer is a tad on the tall side. LG Astronomer and LG Illuminate have exceptional disease profiles and both have the added bonus of OBM resistance.”
RAGT Saki is also a contender for Mr Hoyles. Although yellow rust troubled it early on, once it cleared up it remained relatively disease free.
It is another with biscuit premium potential.
Outside those particularly suited to his soils, Theodore was exceptionally green and, with LG Prince, was probably the pick of the untreated plots. KWS Extase looked ‘clean and even’ all season.
“Theodore was a great colour throughout but with a specific weight of 73.8kg/hl KWS Extase and
LG Astronomer probably have the edge,” he concludes.
Soil film aids potato weed control
Mr Adkins’ colleague James Wilkins says 2020 highlighted the benefit of potato herbicide Emerger (aclonifen).
He points to a challenging season for a number of residual herbicides after the drought prolonged the period of weed emergence. “Weed emergence was extended due to the gap between rain events. Although rainfall was well below what we would expect there was still the odd shower, and every time this occurred we saw some weeds coming through.”
Emerger works by creating a film on the soil surface. As broadleaved or grass weeds emerge, the herbicide comes into contact with the shoot, and is translocated to the meristem growing point. “For the last three seasons at Long Sutton we’ve seen consistent control from Emerger and this has to be in part due to its action. It is less affected by environmental conditions than other residual herbicides.”
That is evident in untreated plots and those using alternative herbicides. Plots treated pre-emergence with 0.5-litre/ha of metribuzin carried a higher black bindweed and knotgrass population last season. “We recommend Emerger is partnered with other actives and extensive commercial experience from Europe has shown robust weed control from a range of Emerger tank mixes. It will be the cornerstone of potato weed control for some time to come, but we must use it as recommended. Ideally it should be applied to a friable, level seed bed prior to crop and weed emergence,” he concludes.