CropDoctor prescribes spring treatments for arable crops

At Errol, owner George Taylor and manager, Brian Dudgeon, at Middlebank Farm, expect winter wheat and barley yields to be above average – although they acknowledge there is a still a long way to go in the season.

Thanks to some tweaks in management, their field of Spotlight winter wheat is looking healthy from field margin to field margin. In the autumn, when the main body of the field was drilled, the headlands were grubbed to rectify some areas of smearing – which made the overall look of the field better this spring.

This and a switch to liquid fertiliser for improved accuracy throughout the field means the crop is looking full of potential.

The Spotlight was drilled on September 26, but its septoria rating of 4.9 was a little questionable. But dry, cool weather at the turn of the month checked this and the yellow rust found early in the season.

This was confirmed with the latest round of rapid qPCR testing, which showed unchanged septoria and yellow rust CropCheck scores in leaves 5 and 4 from the start of the month.

Both diseases can be found, but they are in the base of the plant, but so too is eyespot. It probably isn’t a surprise, given the drilling date and the mild winter weather, but Spotlight isn’t particularly resilient either, rated at 5.

Indeed, few varieties are and as septoria ratings have improved, so eyespot ratings have declined. Only two varieties are rated above six.

Their agronomist, Ben Lowe, said he will look to manage the disease at T1. He is looking for at a prothioconazole based approach, probably 1,0 l/ha of Ascra (prothioconazole + bixafen + fluopyram) with Folpet but he will make a final decision nearer the time.

With T1 sprays still a few weeks away, Ben accepted that disease pressure may change. If the weather turns warm and wet on the run in to GS32, he might have to revise Ascra rates – he also has the option of Revysol (mefentrifluconazole) for highly susceptible varieties where the disease might have established on leaf 4. Again, it will be supported by Folpet.

Bayer’s Grant Reid agreed that, despite low CropCheck scores for septoria and yellow rust, we shouldn’t draw too many conclusions now. “We probably need several rain events for septoria to significantly threaten leaves 4 and 3 but we saw how quickly the disease developed last season when warm, wet weather arrived in late May. We need to remain vigilant," he said.

Despite mixed trials data around Folpet in winter wheat, he felt the susceptibility of the varieties favoured by Scottish markets made it a useful addition.

“It isn’t as strong as CTL, but it is the only multi-site that we have left so it helps protect existing chemistry and it can bolster the activity of any spray mix. Unfortunately, Scottish markets don’t favour varieties like Extase or Theodore where the septoria resilience gives a bit more leeway,” he noted.

Grant agreed and added that Folpet returned mixed results in Bayer trials. But he warned that if you do use a multi-site in any spray mix, it was important not to dilute azole and SDHI rates.

“We need to be applying azoles and SDHIs at rates where they support each other. We need to be applying fungicides appropriately, and we do have some highly dose flexible fungicides.

“But last season with low pressure ahead of winter wheat T1 applications we saw rates where the azole dose wasn’t sufficient to protect the SDHI. We need to protect the chemistry we have as the pipeline is reducing,” he warned.

Mildew threatens at Middlebank

A quick tour of a field of Craft winter barley revealed mildew to be a concern, along with some rhynchosporium on the lower leaves.

It hadn’t been the wettest of winters and the recent cold spell has knocked the mildew back, but both will need checking at the T1, it was reckoned.

Ben Lowe said he will also be looking to preserve as many tillers as possible. This crop is on track for his target of 880 heads/m2 so he will be looking to maintain as many tillers as possible.

As a result, it will be getting a robust dose of Jaunt (prothioconazole + fluoxastrobin + trifloxistrobin) – the stobs useful for some greening properties.

This field of Craft has a planned final application of 45kg/ha of nitrogen, which will be applied at GS32.

OSR flowering extension?

Without a crystal ball, none of us are sure of the future weather, so growers should consider preparing for an extended OSR flowering period.

That was Grant's advice for OSR crops that are reaching flowering earlier than recent seasons, driven by drier spring weather. Despite cold spells bookending March, it was relatively another mild month and one of the sunniest on record, according to Met Office data.

As a result, some OSR crops hit flowering earlier and with further dry weather forecast, it could trigger a host of flowering diseases crops.

Sclerotinia has been the main disease worry at flowering but it is a problem that hadn’t troubled OSR crops over recent seasons. However, growers need to be aware of the disease history on the farm, consider other sclerotinia prone crops in the rotation as well as keeping an eye on the forecast.

Even a dry forecast doesn’t mean that the disease won’t be about. There have been cases of sclerotinia infection even during a dry flowering period.

With rapeseed prices buoyant, Grant said growers won’t want to miss out and he noted that just a small increase in yield would be needed to see a return on investment.

Aviator (prothioconazole + bixafen), Amistar (azoxystrobin) and Filan (boscalid) are all effective against the disease but Grant says where they are best used differs. His preferred approach is for Aviator followed by either Amistar or Filan.

“Persistency is important with the first flowering spray. We know that prothioconazole is effective, but the addition of the SDHI helps. Bixafen bolsters the persistency of prothioconazole, and it is helping with a bit of additional greening thanks to the Xpro formulation,” he noted.

He also pointed out the two actives are also helping with active resistance management and protection and prothioconazole will top up light leaf spot protection.

"A top up can be made around three weeks later to extend protection throughout the flowering period,” he said.

Timing is also important in his view, one reason why he is cautious of a single spray approach. With the main period of petal fall occurring at mid-flowering, early to mid-flower is the best time for the first application he suggested.

“You don’t want infected petals spreading the disease in the canopy, as there isn’t a real curative fungicide option. If the flowering window is short then one spray might suffice, but it is often a bit of a compromise so two is the safer approach.

“With a two-spray approach a top up can be made around three weeks later to extend protection throughout the flowering period,” he added.

Coping with coastal haar

At Scoughall Farm, East Lothian, there was more evidence on the prevalence of eyespot this season. The disease was visible in the base of Skyscraper and testing confirmed it was the W type again.

With the variety having a low rating for eyespot (4) on the AHDB recommended list, it possibly wasn’t a surprise given the weather and the crop was drilled in September.

With the number of sea haars the farm experiences, Scoughall's farmer, Sandy Dale, had to consider a wide range of diseases at T1 timing, yellow rust being a particular concern.

Last year, he used a prothioconazole-based product at T1 and he could go for a similar option again this season. Ultimately, it will depend on weather patterns ahead of the T1, but Bayer’s Craig Simpson thought that this would be a sensible strategy.

“Prothioconazole is a good broad-spectrum option, a good septoria protectant with activity on diseases such as eyespot and yellow rust,” he said.

Skyscraper was also showing septoria and yellow rust in the base of the canopy, but CropCheck scores for leaf four remained low, with it in the protectant phase. Both are visible ,but only in the crop base.

His other 'National Snapshot' variety, Saki, is a little less upright than Skyscraper, but has tillered better. He hoped Saki’s better septoria rating and a well-timed T1 might give him some flexibility to reduce fungicide rates for flag leaf sprays. It, too, was drilled in September and Sandy will wait on the weather before any decisions are made.

CropCheck data will be useful here in monitoring leaf 4 and 3 septoria DNA on the run-up to T2 applications. Last year, it didn’t change any fungicide decisions, but it might this year. “It was interesting to get an idea of the septoria present before it expresses,” he said.

Craig noted that timing would again be all-important with fungicide applications, and stressed that using rate flexibility is only possible if disease doesn’t get away.

“No fungicide can fully eradicate established septoria infection. You’ve got to hit the flag leaf as soon as it is fully emerged. Too late, and disease could already be gaining a hold on the unprotected leaf surface. Too early, and the base of the leaf won’t have completely emerged leaving it unprotected,” he pointed out.

Sandy recognised this and with sea breezes a problem for coastal locations, he invested in a new sprayer. His new Knight 4800 trailed sprayer comes with auto shut off, helping him increase travel speeds.

“A 2 km/h increase in travel speed might not sound that much, but it could be the difference in getting our entire wheat area sprayed in time or not,” he added.

Another problem of a coastal location appeared to be bur-chervil. Over the last two years, this weed had appeared on a number of farms in East Lothian.

It had a treatment of Palio (pyroxsulam + forasulam) in March, but it hadn’t really held it up. With control of the weed early in the season being highly important, Sandy considered his options but both he and Craig are a little puzzled at what they can do at this stage.

One possible cause is min-till but there had not a great deal of trial work to support this. Another possible explanation was mild winter weather encouraging early spring growth of bur-chervil. A herbicide application is being considered with the T0 spray, but with both Saki and Skyscraper a little 'hungry', he didn’t want to stress the crop further with a 'too hot' mix.

With nitrogen prices where they are, Sandy turned to an application of digestate. It isn’t as nutritionally balanced as a liquid, or granular treatment but at just £3/t seemed good value. It’s delivering 145 kg/N/ha, noted Sandy, so is likely to pick the crop up. It will be followed by another 20 kg/N/ha around GS32.

Boghall plots light on disease

At Boghall, Edinburgh, disease levels appeared quite light.

Most wheat plots carried septoria on the lower leaves and yellow rust was only found in Spotlight.

In winter barley some rhyncho was visible but only on the lower leaves, as was mildew. This has been slightly checked by cool weather at the beginning of April but should be factored into disease control programmes.

However, according to SRUC’s Fiona Burnett, the Boghall site probably didn’t reflect what many were seeing on many farms. “The site is quite exposed and crops are a little more open. Crops are not as developed as elsewhere, nor is disease pressure,” she said.

Early drilling into good seedbeds had seen crops get away well and without much in the way of winter weather, many crops are more forward compared with previous seasons. In winter barley, as well as rhyncho and mildew, Fiona had heard many reports of net blotch and brown rust, too, particularly in hybrid varieties.

With buoyant grain prices and well-tillered crops, she said T1 was an opportunity to protect any potential that is there. “Winter barley yield is driven by the number of grain sites, so you want to preserve as many tillers as possible,” she advised.

When it came to fungicides, she would put most of her money at the T1, especially this year with a list of possible disease threats looming. That included newcomer Ascra (prothioconazole + bixafen + fluopyram). It has been approved for a single application in winter and spring barley.

“I can see the argument for holding it back for the T2 application where ramularia has been an issue, but you want the better chemistry at the T1. In our trials rhyncho and net blotch control from Ascra is just a little stronger than previous standard, Siltra (prothioconazole + bixafen),” she added.

With prothioconazole still the cornerstone of barley disease programmes, she said using it in mixtures is important. She notes strobilurins were still providing activity against rhyncho and in some cases net blotch. Spiroxamine is also active against both diseases.

“Using actives in balanced mixtures is the gold standard for resistance management,” she noted.

Lateral flow tests for crops

Bayer are making their CropCheck service available for growers to sample wheat or barley leaves for a PCR test for key diseases. The test is the same principle to the covid lateral flow tests and look for the level of DNA from disease within the sample. But instead of swabs of human material it leaves from growing plants in the field. This detects the emergence of disease before visual symptom can be seen.

It’s a diagnostic tool, not a predictive one for Septoria and yellow rust in wheat, and Rhynchosporium and net blotch in barley, to give a snapshot of disease in a leaf layer to help you understand whether you’re in a more protectant or curative situation.

It should be used in conjunction with the other usual factors, such as weather, drilling date, variety and visual observations to help decide product choice, product rates and help prioritise fields or particular varieties.