Protection is a word we hear often when it comes to disease control – and that was very much the theme for this season’s first leg of Bayer’s CropDoctor tour, in conjunction with The Scottish Farmer.

The open autumn and mild winter has ensured winter crops have got roots down aiding early tiller development and biomass to drive barley grains/m2 and ears/m2 for wheat. At Tealing, Angus agronomist, John Murrie, of Agrovista, is happy with progress so far, as is Agrii’s Greig Baird, at Bonnington Mains, Lothian. Both are keeping their fingers crossed for continuing fair weather.

John Murrie said the season at Tealing was three weeks ahead of 2018. He recorded just 84mm of rain for March, compared to 155mm last year but with plenty of residual nitrogen, the crops appear ‘well fed’.

Mildew was a bigger concern than rhynchosporium in winter barley, he said and, with knockdown options limited, he used a morpholine co-form at T0 to build in protection and will come back in with a mildewcide at T1. “The cold spell in early March checked the disease to a degree, but it is still there. Knockdown options are limited, so I’ll be looking to boost protection at T1. In this region, susceptible two-row varieties, such as Tower and Orwell, remain popular and so particular vigilance is needed.”

In wheat, variety susceptibility is again the factor in T1 decisions. The unique Scottish market means despite susceptibility to septoria and in some cases mildew, varieties like Leeds, Monroe and Barrel remain popular. For Mr Murrie, that meant little choice but to include an SDHI at T1. Both diseases threaten, but septoria levels are varying greatly between September and October-drilled crops.

Yellow rust is visible in susceptible varieties and crops near the coast, but with T0 sprays including a fast moving azole he wasn’t overly concerned.

A note of caution at T1 timing, he said, as leaf three could be out as early as mid-April and growers will need to keep a close eye on crops. “Septoria’s latent phase can be 28 days in cold conditions, but as short as 12 if it is humid. Leaf three could be emerging before growers anticipate,” he warned.

Biomass rich wheat crops are also susceptible to lodging and he feels a robust PGR will be needed at T1 and T2.

“Crops haven’t been hungry this season. Winter wheat T0 sprays included Canopy (mepiquat chloride) and further sprays are likely to include chlormequat with Moddus (trinexapac-ethyl) at T1 and Terpal (mepiquat chloride + chloroethylphosphonic acid) at T2.”

At Bonnington Mains, crops are even further forward and Mr Baird believed winter barley has the potential to out-yield some second wheats.

With winter wheat again there is a big difference in early and later drilled crops with septoria easier to pick out in September drilled fields. Mildew can also be found in susceptible varieties.

Like Mr Murrie, he said the gap from T0 to T1 could be short but his greater concern is it going the other way. His worry was spray gaps getting stretched and fungicides running out of steam.

“A cooler spell could slow disease development. In such conditions, septoria’s latent phase could be prolonged – symptoms won’t be visible but mycelia will be spreading inside the leaf,” he argued.

“It misleads people into thinking that plants are clean and that there is ‘room for manoeuvre’ when it comes to disease control but any fungicide is best used as a protectant. If septoria gets established you’ll never fully recover the situation.”

To keep in a protective position he prefers to ‘frontload’ disease programmes. He always looks to use T0 sprays to damp down disease ahead of T1 sprays and even late drilled crops will get an azole + SDHI + CTL mix such as Boogie Plus (prothioconazole + bixafen + spiroxamine) to keep Septoria and mildew in check.

“My preference is to adjust rates rather than switch to alternative products. All our trials show a yield benefit to SDHIs at the T1, even where disease pressure is lower.”

With winter barley he is also seeing mildew ahead of rhyncho and the weather has been warm enough for brown rust in susceptible varieties. So, he has added a fast moving azole to T0 sprays and will be adding trifloxistrobin (Swift) to Helix (prothioconazole + spiroxamine) into T1 mixtures to top up brown rust protection.

Lodging is also a concern and he will be looking to apply a PGR with T1 sprays. He is a little cautious of their use at T2 with a potential crop effect if it stays dry. On brackling, he said: “We have plenty of biomass in many crops and a ‘growing season’ will only increase brackling risk, especially for hybrid varieties with their height and prolonged stem greening pre-harvest.”

Protection is also playing a part in their approach to nutrition. Both are anxious that dry weather could choke current crop potential and are looking to offset potential stress where possible.

Mr Murrie is concerned with soil pH and will be sampling to check for deficiencies.

Both winter barley and wheat are likely to get an amino acid bio-stimulant (TerraSorb Foliar Plus) and/or chlorophyll enhancer a further boost to rooting and help protect tillers and preserve green leaf area.

Mr Baird will be tissue testing every two weeks to check for ‘hidden hunger’. “What’s important isn’t just getting the balance of nutrients right but also timing them to when the crop needs them most. Our research has shown has shown significant yield responses where nutrient applications are better matched to plant development,” he concluded.

Further threats to chemistry

Following recent news of the revocation of chlorothalonil (CTL), the issue of maintaining disease control and preserving actives is a main Crop Doctor topic.

This is a key component in septoria control in wheat and ramularia in barley, so it is a concern. Although alternative protectants such as Arizona (flopet) will still be available, it is felt they don’t quite match the efficacy of CTL.

Bayer’s James Howat said future focus will fall on cultural control, plus azole and SDHI choice and rates. “Unfortunately, alternatives to CTL are not quite as effective so the industry will have to put more emphasis on variety resistance and drilling date for winter wheat, and trying to reduce stress factors in barley.”

He stressed further threat to chemistry. “CTL’s protective properties help take some of the pressure off azoles and SDHIs, any restriction on its use can only increase that. We’ve always stated that SDHIs need to be supported by robust azole rates and every product in the Xpro range is formulated to deliver a high azole dose.

“However some azole + SDHI co-forms only deliver a 50% dose of azole when used at commercial rates and without such an effective additional mode of action I would consider these as a risk going forward,” he warned.