Combating yellow rust requires a plan

Varieties susceptible to yellow rust will almost certainly need a T0 spray this spring.




Growers should be prepared to adopt robust and early fungicide programmes to tackle yellow rust this spring. James Andrews reports


Freezing conditions over the past month should have held back yellow rust, but growers need to put a plan in place for its control, according to KWS agronomy consultant Bob Simons.


“The cold snap has given a month’s grace by restricting sporulation, but the disease will still be present in the leaf,” he warned at a joint KWS/BASF/Prime Agriculture press briefing.


Half of the UK wheat area was drilled with a yellow rust-susceptible variety, and use of broad spectrum seed treatments and autumn fungicides had been minimal this season, he noted.


Yellow rust was also spotted in crops last November, unlike in the previous season when it wasn’t first detected until spring, suggesting pressure would be higher this spring.


It meant growers needed a plan to combat it, he stressed, which took account of variety susceptibility and sprayer capacity, as well as fungicide product choice and timing.


Potentially growers needed to be prepared to apply products earlier, although it didn’t necessarily mean adding to fungicide bills, he said.


“The first key spray is a strong triazole at T0 to help manage the disease,” he said. That would provide three to four weeks cover, depending on extent of infection, crop growth rate, weather and variety.


A high dose was not essential, but it was critical to get timing and product choice right.


What wasn’t known yet was when that might be needed. In exceptional circumstances where rust was spotted early and was very active it might be as soon as this month, although the cold winter had made that unlikely, he said.


Typically T0s were more likely to be applied in mid to late March. Any earlier could compromise T1 timings. (what do then?)


At T1 if disease levels were high, strobilurin fungicides should be considered in addition to a triazole, remembering the two application limit for strobilurins, he said.


Keeping the gap between T1 and T2 to three to four weeks was critical. “A 10 day delay in application can give a dramatic drop in the level of control – if the weather does intervene you can beef up mixes to help compensate.”


Peter Riley from Prime Agriculture agreed with these sentiments. “There is a serious yellow threat stalking East Anglia and 45% of my wheat acreage is planted with Oakley,” he said. “I’m not a big believer in broad spectrum seed treatments either, so there is a risk.”


Preventing yellow rust from taking hold was much better than eradicating it once it had set in, said Mr Riley. “I can’t abide chasing a disease and it’s 20% more expensive to eradicate – my farmers are pretty happy with this message.”


Consequently, a robust T0 would be required and he would consider using strobilurins earlier. “This year I will probably move strobs from T2 and T3 to T1 and T2,” he said. “The gap is also closing between the cost of triazoles and strobilurins.”


Skimping on fungicide applications would be false economy this year, particularly on rust susceptible varieties, BASF‘s Graham Hartwell said. Independent trials last season showed an average yield response of 3t/ha where fungicides had been applied across 24 varieties.


The impact of cereal price on the value of this input was minimal, he explained.


On larger units where it wasn’t possible for all crops to be sprayed at the optimum time, upping dose would help compensate, he added.


Epoxiconazole-based products were top performers against rusts and septoria, but adding a strobilurin boosted the level of control and increased yield potential, he said.








Application technique 
Wider sprayers and larger farms meant getting application right could be more challenging than with previous epidemics, said Mr Riley.

“Large-scale growers tend to use low volumes and high speeds – there is some evidence to show these reduce efficacy so they may need to reconsider their methods if disease levels are high.”


Speeds of 12-14kph at 100 litres/ha would be acceptable for protectant control, but if there was rust in the bottom of the crop, speeds would need to be dropped and water volume increased, he said.


Mr Simons urged growers to improve coverage by using the correct nozzles. “Where it is possible to use them, angled nozzles will help get the product into the crop.”


Want more information on the yellow rust threat? Go online to our yellow rust academy at www.fwi.co.uk/academy


 

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