The winter wheat disease roller coaster that was 2012 has provided us with many more questions than answers; however, experts agree that identifying risk and focusing on a protectant strategy will be key to disease control.
No two years are the same, which has been demonstrated with venom in recent times and with huge variations in drilling dates this autumn and winter, disease management strategies and subsequent budgets will be heavily dependent on when crops were established.
Identifying disease inoculum risk should be the first consideration when devising a plan for the coming season says Adam Nears, technical manager at Bayer CropScience. “It makes life much easier if you can get septoria and rusts under control early in the programme.”
Last year the main focus up until the spring was the yellow rust and mildew that was running through crops, particularly on susceptible varieties.
“I was particularly surprised at how quickly the situation changed,” says James Mayes, farm manager at Sentry in Bedfordshire and Hertfordshire.
“We were set up for another rust year, but we soon had to tailor our programme as the season developed to take account of the increasing septoria threat. Some varieties were worse than others, but it was defoliating the lower leaves and with each additional rain event, protection became increasingly important.
“Then, after feeling we had done a reasonable job of keeping the crop clean with good products and dose, the visual signs of the brown rust and fusarium showed themselves to levels I haven’t seen before,” he explains.
- Adexar – epoxiconazole + fluxapyroxad
- Aviator Xpro – bixafen + prothioconazole
- Galmano – fluquinconazole
- Tracker – boscalid + epoxiconazole
- Tripod Plus – fuberidazole + imidacloprid + triadimenol
Prevention better than cure
So what does this mean looking ahead this year? What are the risks that can be seen currently in crops? Independent agronomists Peter Cowlrick of CCC Ltd and Richard Cromie of Crop Management Partners have currently found little to no evidence of rust while walking wheats in their respective areas, despite being high risk.
“However, that doesn’t mean that it’s not there,” says Mr Cowlrick. “The focus has to shift to protectant programmes where possible and we now start with rust active seed treatments such as Galmano or Tripod Plus to keep the early rust levels to a minimum.”
Mr Cowlrick points out that septoria resistance pressure on the triazoles is now so high that we are only achieving 50% of the curative activity that was being achieved 10 years ago at 50% label doses.
Despite the addition of new SDHI chemistry pulling eradicant activity up 20-25%, therefore getting close to those previous levels, keeping the disease out of the crop canopy in the first place is still the most important consideration.
“We should be spraying these crops almost like potato blight, getting in with a fungicide every 18-21 days regardless of growth stages. Protecting yield is key and one of the lessons learned from last year is that facilitating an extra pass should be considered,” he explains.
Our panel agreed that a well-timed T0 is the essential first building block in the foliar programme, with the spray timing giving up to 0.5t/ha where it was applied upon leaf 4 emergence in AICC trials.
“The programme should also include chlorothalonil at T0 and at T1 with an azole. At our [Bayer CropScience] trial site at Petersfield we saw a 0.3t/ha response when included at both timings,” says Mr Nears.
“The million dollar question is how much you spend at T1, as it is perhaps the most complicated decision in the fungicide programme,” he adds.
At the T1 timing the focus is now maintaining a robust triazole rate, which should be at least three quarters of the field rate, then bolt on extra products depending on disease risks. These would include a strobilurin for high rust pressure, or an SDHI where septoria is at high levels.
Last year proved to be a season where an SDHI application could be justified at T1, however this may not be the case in a low-pressure situation. “It is an option that involves a higher investment, so I would advise against a blanket recommendation, as a high-rate azole with chlorothalonil is still sufficient in a normal septoria year,” notes Mr Nears.
Flexibility in the face of changing disease presence is something Mr Cowlrick saw paying dividends during the spring of 2012, having switched to an SDHI-based T1.
“In some early drilled wheat and susceptible varieties we changed what was a Tracker-based T1 to an Adexar or Aviator Xpro T1, where applications had been delayed by 10-14 days. We then jumped in with a chlorothalonil + strobilurin + azole at T2 and came back with the prothioconazole-based Aviator Xpro at T3.
“This worked extremely well and we didn’t have any issues with those crops whatsoever,” explains Mr Cowlrick.
He also notes that using Aviator at T1 gave the added benefit of early eyespot control, with its high loading of prothioconazole and in AICC trials gave up to a 5% response over control comparisons.
Protecting the flag
Despite the need to take a flexible approach, our panel agreed that it is still the T2 timing where the largest spend should remain. The plant physiology is something that will never change and the vast majority of the yield comes from leaves 1 and 2.
- Peter Cowlrick, AICC/CCC Ltd
- Richard Cromie, AICC/Crop Management Partners
- Adam Nears, Bayer CropScience
- James Mayes, Sentry Farms (Bedfordshire/Hertfordshire)
“They are the biggest solar panels in the crop and should be kept as clean as possible.
“If timings have gone awry and there is disease bubbling away in the bottom you must hit it with everything you have at T2. Your best eradicant and protectant must be used,” says Mr Cowlrick.
Those best eradicant and protectant products are the leading SDHI formulations, BASF’s Adexar and Bayer CropScience’s Aviator Xpro, and on performance they cannot be picked apart, particularly on septoria control.
“Although it is difficult to separate them on performance, where Aviator Xpro gained an advantage was on price last year. Adexar was around 25% more expensive when considering effective field rates,” says Mr Nears.
Mr Cowlrick agrees, stating that Adexar could have featured much more in his programmes if the pricing was more competitive.
“It was the most expensive option last year and the way the season panned out, it played to Aviator Xpro’s strengths, with a high prothioconazole loading being strong on fusarium. It therefore gives you that flexibility to move it to T3,” he explains.
With many potential winter wheat crops yet to be drilled, there will be changes to disease management plans when establishing in November to February. There is a danger with less yield potential, growers will be tempted to cut back the fungicide spend on those crops.
“If you start cutting that investment, there is no doubt that you will be cutting the yield potential. Particularly with grain prices where they are, we should be prolonging that green area as much as possible,” says Mr Cromie. “Yield is still king,” he adds.
Mr Nears points out that although septoria pressure is likely to be lower in the later drilled crops, growers must not take their eye off the ball. The high disease levels last year will mean that there will be high levels of inoculum in the background, so given the correct conditions it could flare up.
The later drilled crops are susceptible to mildew early on, so a specific mildewcide is something that our panel agrees may need to be budgeted for.
“If mildew does develop on these thinner, later drilled crops, a prothioconazole-based T1 is likely to be my preferred route as it is stronger on mildew,” says Mr Cromie.
“But the specific mildewcide may still need to be included in the programme if it becomes a major problem,” he concludes.
Boosting your bushel
The two leading SDHIs, Adexar and Aviator Xpro both gave useful boosts to what were generally poor bushel weights across the UK last year, which should be considered when justifying the extra spend.
“AICC trials concluded that up to an extra 25% yield response came from using the top two products last year used at T2,” CCC agronomist Peter Cowlrick explains.
The response is believed to come from the improved disease control, but also some underlying physiological benefits from the two products, according to Bayer’s Adam Nears. “Keeping that leaf area greener for the duration of what was an extremely dull grain fill period maximised the potential of those crops,” he adds.
Keep up with the latest arable news.