Cereal growers have an ideal opportunity to use early fungicide applications to capitalise on comparatively lower disease pressure going into this spring.
After a relatively dry winter in many areas so far, levels of septoria and rust are lower than in recent milder and wetter years, but that is no reason to miss the early T0 fungicide, insists Hutchinsons technical development director David Ellerton.
Septoria is still present on lower leaves in many crops and given the challenges of controlling established disease with existing triazole and SDHI chemistry it is vital growers adopt a strong protectant approach from the outset, he says.
The identification of new brown and yellow rust races that resulted in the downgrading of resistance ratings for several important varieties has further heightened the need to keep crops protected, he adds.
“Disease pressure isn’t huge at present, but we’ve seen before how quickly the situation can change. Fungicides don’t offer the same curative ability as in the past, which is why it’s so important to remain in a protectant situation.”
Waiting until symptoms are visible in crops before controlling disease is simply too late, adds Hutchinsons northern regional technical manager Cam Murray.
“Yellow rust in particular can destroy your crop within two weeks if you get control wrong. By the time you see rust sporulating in the crop, disease levels are probably ten-times worse within the leaf. But if you tackle rust early, it is relatively easy to control.”
In contrast to much of England, he says conditions have been relatively mild north of the border, with mildew particularly prevalent on older leaves of wheat and barley.
“Some susceptible crops will need mildew control once they reach stem extension, however really it needs controlling at T0, so is something to watch. If you think it needs control at T0, a morpholine component will be justified. In high-risk crops follow-up with a specific mildewicide at T1 to prevent disease spreading to new leaves.”
Build programmes around multi-sites
In winter wheat, both Dr Ellerton and Mr Murray say multi-site active ingredients such as chlorothalonil or folpet plus a triazole should form the foundation of T0 treatments at mid to late tillering to protect newly developing leaves.
Although chlorothalonil is generally more consistent against septoria, folpet also delivers good results and offers additional benefits from its compatibility with tank mix partners. It has been shown to slow resistance development in some trials too, Dr Ellerton notes.
“We’ve seen good results in our trials from alternating between chlorothalonil and folpet within the spray programme, so it is worth considering.”
Where yellow rust is a risk, particularly in susceptible varieties, he recommends including a rust-active triazole such as cyproconazole, tebuconazole or epoxiconazole to rapidly control any disease present.
Even where varieties have a high resistance rating, Mr Murray warns not to rely on this for control, as was highlighted last year by the emergence of new rust races and revision of rust ratings for several key varieties.
“We’ve not seen much rust yet, but that’s not to say it won’t be there. Any variety is potentially at risk, so don’t assume you’re safe. Much depends on the type of varietal resistance and what races are present this season.”
Keep spray windows tight
Depending on the weather and resulting disease pressure over coming weeks, Dr Ellerton says there may be a case for applying a pre-T0 fungicide based on straight tebuconazole or cyproconazole to the most susceptible varieties or high-risk crops.
“If rust breaks out, it is usually fairly straightforward to control providing you knock it down quickly. Don’t be tempted to wait and let disease establish, or go in too early with the main T0 as this will stretch the window to T1 too far and allow disease in.
“The T1 is usually applied in mid- to late April, so work back three to four weeks from there for your T0 and then consider if an earlier spray is also needed.”
If a pre-T0 triazole is applied, Dr Ellerton says to consider avoiding using another triazole at true T0 in order to reduce the reliance on this chemistry for resistance management.
Strobilurin-based products such as azoxystrobin and pyraclostrobin are good rust-active alternatives with both offering additional physiological benefits to root growth and greening that could benefit backward crops or second wheats at greater risk of take-all.
Strobilurins also offer longer protection against rust than triazoles, typically 14-21 days compared with 7-10 days, notes Mr Murray.
Looking ahead to the growth stage 32 (T1) fungicide, Dr Ellerton says this should again be based on multi-site chemistry plus a triazole.
Adding an SDHI may be beneficial where curative septoria control is required or risk is particularly high, such as in early-sown susceptible varieties, however the final decision should always be tailored to variety and disease risk rather than done as a matter of course.
Barley needs early protection too
Early disease control is particularly important in winter barley to protect the viability of tillers and maintain yield potential, as unlike wheat the crop cannot compensate for losing tillers, says Mr Murray.
An early T0 fungicide applied just prior to GS 30, typically around mid- to late-March, is therefore crucial and has been shown to consistently deliver a 0.2-0.3t/ha yield response, he says.
Products based on cyprodinil and chlorothalonil are generally the most effective option and allow triazole chemistry to be saved for later in the programme. Fenpropimorph is worth including if mildew risk is high, he adds.
As with wheat, an effective barley T0 fungicide to hold back early disease provides more leeway for the main T1 stem extension spray at GS 31. Prothioconazole-based mixtures remain the most effective option in barley and should be combined with chlorothalonil or folpet to form the foundation of any T1 application, Mr Murray advises.
The picture shows David Ellerton in some wheat
