Focussing more attention on early fungicide timings will be key to keeping wheat crops ahead of disease in what is shaping up to be another high-pressure season, says leading agronomy firm Hutchinsons.
While crops are not as advanced as this time last year, most are coming out of winter in good condition and growers need to make the most of early T0 (growth stage 30) and T1 (GS 31-32) sprays to protect and build yield potential, says the firm’s technical development director David Ellerton.
“The recent cold spell has knocked diseases like yellow rust back a bit, but it has still been a relatively mild and wet autumn/ winter, which has favoured disease development. There is a fair amount of septoria on lower leaves, so it looks as though 2015 has the potential to be another high-pressure year.”
With most crops currently at mid- to late-tillering it is likely to be mid-March before the bulk reach the GS 30 spray timing. Dr Ellerton therefore advises growers to remain vigilant over coming weeks and consider a pre-T0 spray if disease pressure warrants it.“The key is to keep control of disease from the outset. Once you let it get away, it will cost a fortune to regain control and may not be possible even with the latest chemistry available.”
Yellow rust in particular is easier to control early in the season and with more aggressive strains now prevalent in the UK, any variety, regardless of its Recommended List rating, could be at risk if disease pressure is high, he warns.
“If you see yellow rust coming into crops, it may well be worth treating early with a cyproconazole or tebuconazole-based product rather than waiting for T0. Once yellow rust gets going, it is very hard to knock out.”
In such situations, the T0 should still be applied at the normal timing, he adds.
Chlorothalonil is the foundation
Reducing the reliance on triazoles means at least half-rate (1 litre/ha) chlorothalonil should form the cornerstone to any T0 spray, says Dr Ellerton.
“Chlorothalonil is relatively cheap, so using it early is a cost-effective way of avoiding ending up in a curative situation, which will cost more to correct and you will struggle to get the efficacy.”
Partner active ingredients should be tailored to specific disease pressure, he continues. Where rust is the main target he recommends including products based on a strong rust-active triazole, such as tebuconazole or cyproconazole. Fenpropimorph-based products are more suitable where mildew is the main threat, while boscalid or prochloraz are effective against eyespot and prothioconazole is useful against early fusarium.
There is also renewed interest in the early use of strobilurins, which could play an important role in helping growers to break through the current plateau seen in average UK wheat yields, Dr Ellerton notes.
“Strobilurin use waned when they lost their efficacy against septoria several years ago, but they still do a good job against rust and offer positive physiological effects on rooting and greening. Early application is key to maximising these benefits though.”
There is also evidence to suggest strobilurins, pyraclostrobin in particular, can help slow septoria progression when applied at an early growth stage, further improving their potential to be used in a protectant situation, he says.
Triazoles versus SDHIs at T1
Chlorothalonil should again form the foundation for T1 spray programmes, with partner products based on a robust triazole dose, SDHI or a combination of both depending on disease pressure at the time, says Gloucestershire-based Hutchinsons agronomist Patrick Levinge.“We’ve learnt from past years that triazoles in eradicant situations are failing and SDHIs can give good control. But above all, chlorothalonil is still the base for disease control, especially against septoria.”
Under relatively low disease pressure a chlorothalonil plus triazole-type approach can deliver good results, he says, while SDHIs are especially useful where more curative activity is needed, for example where a T0 hasn’t been applied or the T1 has been delayed.
Penthiopyrad or fluxapyroxad-based products offer strong curative efficacy, while isopyrazam has slightly more persistency which may afford some extra leeway for T2 sprays, says Dr Ellerton. Generally rates should be at least 50% of full label dose, although this will vary by product and disease pressure, he adds.
Cutting corners is false economy
Mr Levinge cautions against unnecessarily cutting costs at key fungicide timings, especially as recent years have highlighted how quickly weather and disease pressure can change.
“When you consider the total growing costs for a crop of wheat can be anywhere from £800/ha to £1,200/ha, the risk of failure caused by cutting corners and allowing disease to get established to save £20-50/ha makes the extra cost of a robust fungicide strategy actually seem relatively small.”
Dr Ellerton adds: “Invest your money in the crop wisely early on and that will pay for itself in the long-term and may give you the scope to trim costs later in the season, especially on varieties with stronger disease ratings, such as Skyfall, Revelation, or Cougar, for example.
“The average yield response from fungicides in trials last year was around 4t/ha and we could well be at that level again this season, so cutting costs for the sake of it is false economy.”
Looking further ahead to the T2 fungicide, both Dr Ellerton and Mr Levinge agree that growers should base programmes around SDHIs with strong curative efficacy, such as fluxapyroxad, while bixafen-based products in combination with prothioconazole and tebuconazole offer all-round disease control.
“Whatever approach you take, make sure spray intervals are not stretched much beyond three weeks,” says Dr Ellerton. “Even the best SDHIs don’t have the curative ability that triazoles used to offer, so if it looks as though intervals could get close to four weeks or more, consider going on with a holding spray of chlorothalonil, with or without a triazole, as leaf two emerges at the so-called T 1.5 timing to ensure disease doesn’t get established.”
