JUST TWO weeks prior it looked like crops were going to be racing their way towards T1 and even T2 spray timings, but cold easterly winds had put most crops to sleep – at least until the weekend past!

The cold spell, including ground frosts, had checked winter barley and wheat disease but they have not hit yield potential and may even have had the effect of reducing disease threat – but only for now. Last weekend's warm sunshine brought upon a race through the growth stages for most crops in Scotland.

That was the main conclusion from the second leg of the CropDoctor North tour, facilitated by Bayer at sites near Edinburgh and Dundee.

At both Ratho and Tealing it was largely a scene of green, uniform crops, though winter barley with its softer growth was showing signs of ‘tipping’ due to the cooler weather, but agronomists – John Murrie, of Agrovista and Greig Baird, of Agrii – both believed that potential is there for winter crop yields to exceed farm averages.

This means that it is well worthwhile protecting these crops, though it is going to be critical to both tailor disease spray programmes and crop nutrition to fast-changing crop conditions as we approach that critical time of year for plant extension.

At Ratho:

At Ratho in Midlothian a combination of cool weather and T0 and T1 sprays had done their job on winter barley. Following Vareon (tebuconazole + prochloraz + proquinazid) and Phoenix (folpet) at the T0 and Helix (prothioconazole + spiroxamine) + Swift (trifloxistrobin) mildew was now under control and there was little evidence of rhynchosporium or brown rust either, with that latter disease a concern at the last CropDoctor tour just two weeks prior.

In winter wheat at Bonnington Farm, it was a similar picture with septoria confined to the older, lower leaves of plants, said crop advisor, Greig Baird, of Agrii.

Given the recent slow down in growth followed by much warmer weather last weekend, the big question is what will happen between GS31 and GS39. Mr Baird said if the weather turned warm and humid, the disease risk could ignite and rainsplash would spread septoria in wheat and rhyncho in barley onto the main ‘yield generating’ leaves.

In a crop of the old stager, Instabraq, as a second wheat he said that the septoria pressure which had been high, had been put into a latent phase by the colder weather, but could explode and that was part of his thinking when planning the T1 sprays which were due at the end of last week.

He added that Agrii’s septoria prediction tool – which is part of the digital platform, Rhiza – was already giving a ‘heads up’ to what might lie ahead. It overlays local weather data from the previous three weeks and the future forecast, while cross referencing this with variety susceptibility and drilling date. “Septoria needs about 220 day degrees from infection before symptoms become visible. Depending on the weather, that latent phase typically ranges from 14-28 days which is a wide window," he said.

"The important thing is to keep septoria pycnidia on the lower leaves, which is why front-loading programmes will be so important. The chemistry set available to us has a maximum of three weeks cover if disease pressure is high and maybe up to four weeks at lower levels, so it's crucial to be agile about what we do and how we use it."

As will be timing, he added. Ideally, intervals should be kept to a maximum of four weeks: “If we get warm, humid weather post GS32 applications, the gap to GS39 could be less than three weeks. I would be vigilant and check crops for leaf three and flag leaf emergence. Don’t rely on node development as it is only a guide.”

For the key T1 and T2 winter wheat timings he will be relying on primary azoles such as prothioconazole and expoxiconazole with SDHI partners such as bixafen and fluxapyroxad. He will adjust rate based on field, variety and disease pressure in what he described as ‘agile agronomy’.

“Tools like Rhiza help improve our decision-making. Unfortunately, many of the varieties on this site are vulnerable to septoria but disease severity is also influenced by weather, location, cultivation and drilling date. Where the pressure is lighter, I would prefer to reduce the rate of an azole + SDHI mix than move away from an SDHI mixture as currently this mode of action has most activity against the disease.”

Given crop density and the potential for rapid growth, he added that the T1 sprays were likely to get a follow up PGR in the form of Alatrin Evo (trinexapac-ethyl) + 3C (chlormequat) after T0 applications shortened and stiffened crops. This could be particularly important with ‘leggy’ varieties such as Istabraq.

The forthcoming T2 spray for winter barley will be an azole +SDHI mix with rates again adjusted to reflect disease pressure. Bravo (clorothalonil) will be added to provide ramularia protection and hybrid varieties might also get a strob as a further safeguard against brown rust. “There’s only one hybrid variety rated above a six for the disease,” he cautioned.

Rhiza’s prediction for warmer weather in his area is also focussing his mind on ‘hidden hunger’. A particular concern is rapid growth when the weather warmed up and the availability of magnesium.

“It has a critical role in chlorophyll development and at the peak time of photosynthesis for the top two leaves crop, uptake is 25-40kg/ha. If the dry weather has locked it up, T2 sprays will need a foliar application, zinc and copper are also important elements for greening. Tissue testing ahead of GS39 will be important.”

At Tealing:

Near Dundee, at Whitehouse Farm, the crops were a little further behind being closer to the North Sea and suffering under what had been a fairly constant east wind for almost a fortnight since the last CropDoctor visit.

There, Agrovista's John Murrie said that the weather had ironed out some of the disease issues, as it often did in this area. Given that crops were all looking well, if a little 'wind-tipped', he said that, now that all the 'big bills' had been spent getting the crop to this stage, the effort now should be to protect that potential.

He was hoping for some rain to wash liquid fertiliser in to the soil and this would help keep the crops ‘fighting fit’ by both encouraging growth and allowing the chemistry to fight disease.

Keeping the crop growing was a focus and he said that tissue testing was increasingly becoming important to fine-tune nutrient regimes, especially this season.

He said that for a tissue test costing £20, it was a 'no brainer' in being able to tailor fertiliser programmes to suit each field and crop. His main concern was that a number of nutrients, while in the soil in enough quantity, might be ‘locked up’, thus reducing what is available to the plant.

As a result, he will be tissue testing ahead of both T1 and T2 timings – he send his samples to Lancrop for a one week turnaround. “Increasingly, we are recognising that it is balanced approach to nutrition that is needed to optimise crop performance. In the past, we have been too focused on some key elements but overlooked the fact that each has a role in producing healthy plants capable of soaking up sufficient moisture and sunlight to deliver yield and grain quality.

"It will be important to check for any crop deficiencies. We hear so much about the yield plateau, but we have more to do in fine tuning nutrition to the situation each crop faces. We also must remember every field is different.”

Of particular concern was magnesium at T2 – an essential element for photosynthesis. Zinc was another element which had been showing deficiency this season.

Much of this fine tuning he said would likely be in foliar form. If it stays dry, this will be the best way to get the necessary nutritional top up into plants, adding that newer products had improved formulation making them far more mix compatible.

Crops were a little scorched by frost but still hold good potential and this, along with T0 and T1 sprays, had checked yellow rust and septoria in wheat, rhynchosporium in barley and mildew in both. “Early sown wheats were carrying more septoria early in the season but that has evened out,” he said.

Again, yield potential was looking good, but the question now was keeping it that way. With little in the way of curative options for septoria in wheat and rhyncho in barley he said timing was critical. “Whatever the target leaf is, if you go too early you won’t fully protect it and if you go too late, then disease will be established," he argued.

“No fungicide is fully systemic, so if the leaf isn’t fully out you’ll only protect what is there. Added to that, fungicide protection is four weeks at best so if the gap to the next application is stretched then it only increases the exposure further.

"That is the other problem – if diseases like septoria get in you’ll never get them out – not even with an SDHI.”

His winter wheat T1 and T2 sprays will include an SDHI which he thinks is important, despite septoria being in check currently. “The risk is just too great for me as the best laid plans can go wrong, especially with our unpredictable climate. But there’s also the crop potential to factor in.

"Without access to high premium markets, yield is king so you don’t want to take any chances. Also we have to remember that a number of fungicides do have physiological properties which could help.”

Winter barley T1s at the farm – mainly KWS Tower grown for feed and hence yield – had a prothioconazole mix with strob and SDHI plus PGR. This is likely to be followed by an azole + strob mix at T2 with CTL being added to guard against ramularia.

An SDHI could be added if rhyncho is re-ignited by warm, wet weather and both winter wheat and barley could need a further growth regulation with an ethephon-based product – but the question is 'when?' Ideally, he said he would hold that off until T2, but the unknown is the weather and may use it earlier if needed.

“We’ve got some very lush crops and if we get a period of warm, wet weather, these crops could really kick on again. If so, I'll consider a T1.5 application and possibly add in a touch of CTL just to keep a lid on disease. Current crop potential makes it justifiable,” he concluded.