Encouraging root structure a priority in late-sown crops – The Scottish Farmer – Cam Murray

After autumn rain halted drilling operations January delivered a country average of 209.5 mm, 135% of the 1961-1990 mean and the Foehn effect saw temperatures reach 18.7°C at Achfary, in December (a UK record), and 15.5°C on January 7.

The result is now big differences in late drilled winter wheat and barley, and root structure could limit the capture of nutrients and needs to be the focus for Scottish arable farmers over the next few weeks.

That’s the limiting factor for winter wheat and barley right now, according to Hutchinsons regional technical manager, Cam Murray. With late drilled winter wheat and continued wet cold soils limiting root and tiller development, these early season impacts have already potentially knocked 20% off final yield. The task now is not to let that slip further.

With phyllochron intervals (when tillers emerge) driven by thermal time, some September drilled wheats are close to three tiller stage, but late drilled winter wheat is nowhere near that. “You won’t see the first tiller until you get three leaves. Many wheat crops are still at the two-leaf stage,” he noted.

For winter barley, it’s a slightly different story, as it will have produced and set all its tillers before the winter period. With no ability to compensate by higher grain site production or more tiller development, he said that early N should be considered a key focus point.

With later drilled wheat and barley crops, he would like growers to use all the tools in the box. That includes a tailored nutrition strategy backed by PGRs and bio-stimulants.

He added that a shallow root structure made nutrient capture difficult, so helping roots develop early to improve nutrient uptake is particularly important this season. He would recommend an AN sulphur-containing product.

“These get into the plant a little quicker, giving an early hit of N and sulphur assists this too. Sulphur’s longevity also helps the uptake of a range of nutrients.”

He advised a little and often approach and will be looking to get an early application on in crops he’s handling. But the balance will depend on each crop.

For backward wheats, he advised about 80% of a typical first application. “I’ll be looking at N rates of 40-50kg N/ha and the following on from there. It will help get plants moving in this backwards year but the last thing you want is encouraging excessive apical growth in shallow-rooted plants!”

Winter barley was mostly established in decent conditions before the weather deteriorated, so he said a more traditional approach to nitrogen applications, with earlier and higher doses of N, should apply with this crop. On lighter soils, he suspected manganese deficiency might an issue, so urged growers to be mindful.

A PGR will go on at the TO timing, plus a bio-stimulant. Not all PGRs are approved for use at GS30, so Mr Murray said he would opt for a low-rate trinexapac-ethyl because of its gentle nature on the plant early on.

“The aim is to stimulate root growth whilst in the foundation phase. We can manipulate the plant up to stem extension, but after that stage, apical dominance takes over and further manipulation to rooting and tillering survival is not possible,” he pointed out.

“We also have to remember that 90% of lodging in UK crops is root lodging. Starting off your PGR programme here isn’t a bad idea, even for more backward crops.”

The bio-stimulant will be a stabilised combination of phosphate and zinc. Despite generally uneven results from bio-stimulant trials, he said benefits had been found. “Such treatments are a way of stimulating small rooted plants. In our trials, we have seen yield responses of 0.3t/ha consistently over the last three seasons of assessments,” he added.

Another urgent task will be addressing weed concerns. Many conventional drilled crops didn’t get autumn residual herbicide treatments, so a number of crops will need a tidy up of annual grasses, wild oats and broad-leaved weeds. But, he warned growers need to be careful with timing.

“In many cases, we’ll be looking at mesosulfuron-methy with iodosulfuron, and possibly a residual component as well. These contact products are potentially hot to the crop – particularly in a year like this with some root pruning and general lack of crop development,” he said.

“Stressed crops have shown in the past that they can be sensitive to these spring mixes some warm weather and early N will help in alleviating these symptoms occurring, he noted.

Disease wise, he said growers shouldn’t overlook septoria in winter wheat. “I think the term low Septoria season is a little misleading. The disease is always there in the background, carried over on crop debris from the previous season.

“The question is more at which time Septoria will express itself, which is down to a number of factors. Clearly, the weather is important but variety resilience and drilling date also impact when this occurs.

“The slight concern I have is that some might see any late drilled variety as at low risk, but I wouldn’t say this is necessarily the case. A variety like Barrel, with a septoria rating of 4.3, could be exposed to a significant threat if wet and humid condition prevails during April and May.”

Using varietal rating and drilling date does provide flexibility in programme choices from GS30 (TO) through to GS39 (T2). He saw some flexibility in products and rates but urged not to gamble too much with fungicide rates in the hope of saving a few pounds.

“With the long-term average response to fungicide programme at 2 t/ha it can be a false economy by not protecting your crop properly. If Septoria gets in yield losses will outweigh fungicide spend significantly,” he concluded.

Bayer’s Grant Reid added that growers should also add stem-based disease threats to the fungicide checklist this spring. He thought mildew was making a comeback, but also highlighted other stem-based disease risks, such as eyespot.

“Both are probably benefitting from mild winters, and with eyespot rotations too. We’re now seeing eyespot in spring barley, so it does appear to be on the increase as well.”

Mildew isn’t usually a significant yield robber and nor is eyespot if crops don’t fall over, but both do need managing, said Mr Reid, who added that mildewcide options are now limited.

“Prothioconazole is still highly effective against the stem-based complex and we have a number of options to suit a range of disease profiles in wheat and barley. With two complementary SDHIs, Ascra (prothioconazole + bixafen + fluopyram) is still an exceptional Septoria protectant and covers the stem-based complex and yellow rust too.

“Where barley is concerned, Siltra (prothioconazole + bixafen) at 0.4 to 0.8 1/ha dependent on variety disease ratings and disease risk is sufficient to meet both foliar and stem-based threats,” he said.