Colder weather sees wheat fungicide plans back on track

Despite one of the mildest winters leading to doom-laden predictions of rampant disease, wheat disease control plans are back on track as the T1 timing approaches.

That’s the general view from the field as T0 sprays are being applied, with the fire engine situation that they were predicting earlier in the year having failed to materialise.

The reason? A cold, dry spell in March, which helped to slow crop development and dry up much of the disease that had been causing concern – taking the pressure off the need for very early fungicide applications and allowing growers time to hit the optimum spray timings.

See also: The ultimate guide to crop disease and pest forecasting tools

The arrival of colder temperatures at that stage was good news, believes Hampshire-based AICC member and independent agronomist Nick Wall, who points out that it eliminated the urgency for early treatment and prevented spray intervals being stretched beyond the optimum three weeks.

Cost savings

“Growers can now use these tight gaps to their advantage and look for cost savings, rather than being concerned about leaving crops unprotected or being forced into applying extra sprays,” he says. “It also means that they can shop around for fungicides and make good use of the price differences that exist between products.

“In the right situation, it’s possible to save anything from £2-£7/ha on the T1 spray by switching products or tinkering with rates.”

Further flexibility comes in the form of variety choice on some farms, he adds. “The dirtier, more rust susceptible varieties might have warranted a triazole/chlorothalonil mix at T0 and could still require an epoxiconazole-based SDHI at T1.

“However, the more resistant varieties, such as Skyfall, Crusoe and Costello, were fine with just chlorothalonil at T0 and won’t necessarily need an SDHI at T1.”

Mr Wall is hoping to keep fungicide costs below £100/ha this year on many of the farms that he visits. “We set a base programme at the start of the year and then react to the weather and the crop nearer to each spray timing. Given the changes in pathogen races and their varying sensitivity to fungicides, keeping a degree of flexibility is important.”   

While two SDHIs are currently in his plans, for both T1 and T2, he notes that dry conditions will allow him to reduce rates and keep to the budget. “A Tracker (boscalid + epoxiconazole)/Adexar (epoxiconazole + fluxapyroxadmix) at T1 worked well last year, with the rate of Adexar adjusted according to the situation.”

Yellow rust threat

Paul Gruber, agronomist with ProCam, agrees that the cold snap helped to re-set crop growth stages, but he warns that there is still enough active yellow rust around to be a concern – especially as new races have been identified which could bring some surprises.

“We’ve lost some of the bottom leaves that were carrying disease, but crops aren’t clean, with septoria and rust still evident. Only the mildew threat has really diminished.”

As a result, many of his chlorothalonil-based T0 sprays were boosted with a bit of triazole, to clear up any existing infection, and the majority of his T1 treatments are likely to contain three modes of action.

“It’s not an option to lose the septoria battle so early on, as you can’t recover,” he says. “There has been some debate about whether an SDHI is needed at T1, but under significant disease pressure it will be required.

“Of course, an SDHI is a given at T2, and on dirtier varieties it will be required at both T1 and T2.”

For this year, his preference at T1 is for an SDHI/triazole mix with chlorothalonil. “The triazole element should be at a minimum 75% dose, with the SDHI at 50%. And the addition of chlorothalonil is even more pertinent now, after the discovery of the first septoria isolates in England which are less sensitive to the SDHIs.”

Either penthiopyrad or isopyrazam will be used as the SDHI component, he reveals. “Penthiopyrad has a root development benefit, which might be especially beneficial in poorly rooted crops after the wet winter this year. The triazole element will be epoxiconazole where rust is a threat, or prothioconazole.”

Another option is to use a boscalid-based T1, especially where eyespot is deemed a threat, which will bring the fungicide spend down a bit, he notes.

Mr Gruber accepts that cost savings are possible on cleaner and later drilled wheat varieties, but reminds growers that they must balance their disease control strategy with the need to protect the existing chemistry for future years.

“We are going into uncharted territory,” he warns. “We have been told to expect further changes as far as the diseases and fungicide efficacy are concerned.”

Fortunately, fungicides still give a good return, even where disease levels are very low, he remarks. “No-one wants to spend money on crops which have such a low end value, but the fungicide investment always pays for itself.

“What’s more, getting on top of any septoria and rust at this stage gives you more choice later on in the season.”


Crop Watch

Keep track of the disease pressure and spraying spraying progress as the season unfolds with Farmers Weekly’s Crop Watch. Each week, our agronomists give a regional update at www.fw.co.uk/cropwatch

Also brush up on your fungicide knowledge with our Fungicide management in cereals academy, consisting of five e-learning modules. Take the test and earn cpd points at www.fwi.co.uk/academy