Rapidly advancing crop growth after a relatively slow start this spring could concertina fungicide timings and extra care must be taken to avoid missing key growth stages, leading agronomy firm Hutchinsons warns.
While advanced wheat has already reached the T0 fungicide timing (growth stage 30-31) in many regions, some crops, particularly those drilled late on heavy land, are less well developed at nearer GS 25-26 and only just starting to get going at the time of writing.
Crops will catch up quickly as day length and temperature increases though, which could result in relatively short gaps between the early spray applications, the firm’s northern regional technical manager Cam Murray says.
“Last season was a slow burn in terms of crop growth and this season has been even more so. But things are picking up quickly, so spray windows could get quite tight as crops race through growth stages. It is vital growers apply fungicides at the right growth stage, regardless of how long it is since the last spray.”
But wet ground conditions and a changeable weather forecast threaten to further disrupt spray windows, he adds.
“Most wheat in northern England and Scotland will reach the T0 fungicide timing next week (w/c 11 April), but at the moment it’s questionable whether many growers will be able to get on the land.”
The growth stage 32 (T1) spray timing is typically three weeks after T0, putting it around late-April in many areas, but this spray interval may be narrower if the T0 is delayed.
Septoria pressure still high
Septoria tritici pressure at the base of crops remains high given the relatively mild and wet winter so any compromise to early control could prove costly, says technical development director David Ellerton.
“Fungicides don’t have as strong a curative ability on Septoria as in the past so growers have got to try and keep in a protectant situation by getting on top of disease early and keeping spray windows tight throughout. Ideally the gap between sprays shouldn’t extend beyond three weeks if possible; the longer the delay, the more curative action will be needed.
“Septoria is the dominant disease and even varieties with a good resistance rating of six can still be badly affected, so don’t compromise fungicide timing.”
Rust and mildew were rampant earlier in the season, but Dr Ellerton says incidence appears to have been dampened down by the spell of colder weather last month. Any remaining disease should be relatively easy to control by tweaking product choice at the T0 or T1 timing.
Tailor product choice
Mr Murray advises growers to tailor fungicide choice to the strengths and weaknesses of individual varieties and treat each crop on its own merit rather than taking a blanket approach at the main fungicide timings.
“It might be a bit more difficult for growers with large areas to cover to keep adjusting mixes and rates, but it is a far more effective way of reducing costs than just cutting rates across an entire area, which could compromise disease control.”
Early use of a multi-site protectant, such as chlorothalonil or folpet, at T0 and T1 should form the foundation of any spray programme, with additional chemistry choice tailored according to variety characteristics and rotational position, Dr Ellerton advises.
If the T0 has been compromised in any way and curative control is required both experts agree it is worth using an SDHI at T1 to bring disease back under control, however where pressure is lower there may be scope to use a more cost-effective triazole mix instead.
“Where margins are tight there might also be leeway to save costs by reducing fungicide dose under low disease pressure situations on less susceptible varieties, but don’t go below 70% of full label dose for triazoles or below 50% dose with SDHIs,” Dr Ellerton continues.
“There’s no sense putting the entire spray programme at risk by trying to save a few pounds. As soon as you start compromising sprays and timings it puts more pressure and cost on following sprays and risks not getting the control required.”
Including a triazole or strobilurin at T1 is worthwhile if additional rust control is needed, while penthiopyrad is a good SDHI option that offers septoria and eyespot control as well as impacting on root development. Prothioconazole is also effective against eyespot, as well as fusarium, he notes.
Fluoxastrobin or azoxystrobin at T1 are other options to consider where take-all risk is high, such as in second or third wheat situations, he adds.
Dr Ellerton says T2 (growth stage 39) flag leaf fungicides should nearly always be based around an SDHI for the curative control offered, unless disease pressure is very low.
That is echoed by Mr Murray, who says that while it may be possible to use cheaper chemistry at T0 or T1, there is nearly always a need for strong curative action by the time crops get to the T2 timing, so using an SDHI is worth the investment.
“The flag leaf contributes 35-40% of final yield, so it’s vital to keep it as clean as possible.”
There can be a physiological benefit on extended crop greening from early use of SDHIs and strobilurins, which may influence product choice but should not be the driving factor, Dr Ellerton adds.
Barley looks good
Winter barley appears to be faring well so far this season and although some rhynchosporium is present, earlier rust and mildew has abated leaving relatively low disease levels in most places.
Most crops have received their T0 fungicide, with the T1 due in the next two to three weeks, says Mr Murray. “Flag leaf emergence is determined by day length as it is in other cereals, however winter barley has the potential to quickly race through growth stages as soon as the sun comes out. Even backward crops will soon catch up.”
Early fungicide sprays are critical for maintaining tiller numbers in barley and Dr Ellerton says it is worth investing in an SDHI plus triazole, such as prothioconazole, at T1.
