SRUC trial site shows spray timing critical to hitting disease

One of the key messages currently is that farmers need to get their application of T2 and T3 sprays right to keeping on top of disease this summer.

“If farmers are just a few days out of the optimal window then yields will be hit,” explained Bayer's Grant Reid. “We can be up against the weather for spraying and so if it is a choice, then I would recommend applying slightly earlier rather than later.

"Recent rain showers will be helping septoria to spread up the leaves with wheat varieties such as Skyscraper and Barrel vulnerable to disease spread."

For susceptible varieties, like Elation and Skyscraper, where septoria might establish on leaf 2, then Grant said some curative activity is likely.

In this situation you could consider increasing rates of Ascra (prothioconazole + bixafen + fluopyram) above 1.0 l/ha, or moving to more curative options, like Revystar (mefentrifluconazole + fluxapyroxad), or Univoq (prothioconazole + fenpicoxamid). Where septoria pressure is lighter, or for better rated varieties like Insitor, then curative activity is probably unwarranted.

At SRUC’s trial plots at Boghall, most of the crops are performing to their forecasts. The Crop Doctor team took a look at the untreated trials to gauge the disease burden on the crops which had not received any sprays.

The popular winter wheat variety, Barrel, had septoria and mildew on the plants. Levels of septoria were not surprising since the variety had a low septoria rating of 4.3.

Experts also described the outbreak as 'textbook mildew'. They recommend if growers find consistent and higher levels of mildew than usual, then they should consider a mildewcide to prevent a drop in yield.

However, many farms will know how mildew affects their crops, with many seeing little impact beyond the cosmetic. Application of a prothioconazole spray at T2 is a good option for tackling mildew if you decide to take action.

If left untreated and able to spread through the crop, then not only is a yield drop of half a tonne per ha is possible but also quality can be affected too.

Next, at the trials site, was Skyscraper, which is a popular winter wheat variety on many Scottish farms this year. As the name suggests, it is a tall variety and sits between Extase and Barrel on the septoria resistance ratings. This crop expressed low levels of yellow rust on plants which seems to be common on crops that were early sown in 2021.

The Spotlight variety trial showed a higher prevalence of yellow rust on leaf three. This could be followed by Septoria which usually expressed after rust in plants. If left untreated, then yellow rust could hammer yields by up to 70%.

Spring barley

The spring barley crop was well established at the trial site after being planted of March 25.

Craig Simpson, from Bayer, said: “The crop is looking well, it has been slightly dry but the recent rain helped to reduce some of the crop stress, although a post-emergence herbicide will now be needed.

"It is recommended that the spring barley T1 is applied at the end of tillering, but currently there isn’t a huge amount of disease in spring barley but this will change as the season progresses.

"If you don’t keep an eye on your timing, the crop can really jump at this time of year and you lose the optimal window for fungicide applications and disease control,” he pointed out.

He also felt that growers should adopt a two-spray approach for this crop to avoid a potential timing compromise and strong malting prices.

“I can understand the attraction of just one application, but if the weather turns it can see a compromise in timing and protection, and prices are good at the moment.

"Even for those that have forward sold any extra yield offers further market opportunities. Two applications of a good all-round protectant, like Siltra (prothioconazole + bixafen), is good value for money,” he added.

Crops across the country

Turning to the situation for cereal farmers across the country, agronomist Ben Lowe believed there was a big difference in early and late sown winter wheat varieties.

Early sown crops continued to build on the good conditions of early autumn and were ‘motoring on’. They are full of potential and good weather during grain fill should see some good yields come harvest, he said.

More good news is that they are growing away from septoria in the base of plants and T1s were well timed to afford good protection to leaf 3. But he does sound a note of caution with timings.

He said flag leaf emergence could be seven days ahead of typical calendar dates. “There is the danger that the flag leaf could be fully out earlier than growers expect, so a timing compromise is possible. Even though the gap from T1 might be quite short, septoria could establish inside an unprotected leaf.”

With transfer still possible and buoyant grain he is looking at the most robust septoria fungicide options for T2 sprays. “Wet weather could splash the disease up the plant so I will probably opt for Univoq (prothioconazole + fenpicoxamid) or Revystar (metentrifluconazole + fluxapyroxad).”

For more backward wheats, there are more fungicide choices. They are not as well developed nor do they carry the same amount of disease in the lower canopy.

Flag leaf emergence is also likely to be more in line with calendar dates, so Ben has another week to think through the decision.

Current grain prices could see him go the Univoq or Revystar route again, equally he could go with Ascra (prothioconazole + bixafen + fluopyram) or Elatus (prothioconazole + benzovindiflupyr) for susceptible yellow rust varieties.

Both early and late drilled varieties could see the addition of a herbicide to T2 sprays. Ideal growing conditions for crops had also been ideal for some weeds too.

Ben noticed plenty of broad-leaved weeds lingering in wheat crops – particularly groundsel and chickweed – herbicides struggling to control them with ideal growing conditions.

“Ideally, you want to hit broad-leaved weeds when they are small. But this year additional activity may be required – the conditions have been particularly favourable this season,” he said.

Winter barley

Winter barley crops also look full of potential and the tendency to drill them over a shorter window means there isn’t the same diversity in development or disease,

Disease incidence and severity isn’t as severe as some seasons, and probably no surprise given the dry spring. But he urged growers not to be complacent.

Like septoria in wheat, rhynchosporium is a disease that can quickly be splashed up a plant and the disease is still present in the canopy base.

He also advised growers to be vigilant with ramularia. It is another disease that likes wet and humid weather but also has a range of stress triggers, including drought and light intensity.

Prothioconazole remains a strong rhyncho protectant and this will be the cornerstone of winter barley T2 sprays. He’ll also add in some folpet to boost ramularia activity.

“Typically, I will look at something like Jaunt (prothioconazole + fluoxastrobin + trifloxistrobin) but it could be Siltra (prothioconazole + bixafen) or just straight Proline (prothioconazole),” he said.

Winter barley crops are also suffering the same weed burden as spring barley, so additional activity is advisable. Ben recommended a separate pass ahead of T2 sprays to avoid damage to the awns.