Why fungicides still pay – even in tight margin seasons

“Growers should not be lulled into a false sense of security following the relatively low disease incidence seen last season. The situation could be very different with more normal weather patterns this season,” warns Hutchinsons agronomy innovation director, David Howard.

With many wheats drilled early last autumn and generally good establishment, septoria risk could well be higher in larger biomass crops, as could yellow rust risk, especially in varieties affected by the breakdown of the YR15 resistance gene.

Although there is not a huge amount of information confirming exactly which varieties carry the YR15 gene, and how reliant they are on it, some big names appear to have been affected, given the reductions in yellow rust ratings on the latest AHDB Recommended List. 

Varieties such as Champion, KWS Dawsum, LG Typhoon, and Bamford, have all seen revisions, and are varieties where we saw issues in the field last year too. 

Anyone growing a variety that has seen revisions to its RL score will have to be particularly vigilant with early disease control this spring, especially where other factors favour higher disease pressure. 

David acknowledges that increasing inputs at a time when gross margins are already strained is unpalatable, but insists maintaining yield will be essential if disease pressure builds. 

“Fungicides are often adapted according to disease pressure each season, but they’re a relatively safe bet in terms of investment. They are the second biggest returner after nitrogen,” he says.

“At a wheat price of £160–£170/t, we are looking at a fungicide return of £346–£368/ha.”

Use chemistry wisely to its best effect, considering the strengths of individual actives, and where they are best used in the programme, he advises.

“Assess individual fields and varieties for risk and look for efficiencies across all inputs, rather than arbitrarily reducing the fungicide budget, given they offer one of the most consistent returns on investment.”

Ear fungicides (T0/pre-T0) should generally focus on yellow rust control, with septoria pressure remaining the biggest determinant of mainline T1/T2 fungicides.

However, if septoria pressure is particularly high by T0, growers should consider including folpet to manage this. Don’t overlook mildew pressure either, David notes.

“Beware label restrictions preventing use of some products before GS 30; biological controls may provide another option to help keep disease at a manageable level when fungicide options are limited, although remember they are purely protectant and not curative,” he says.

Optimise dose for longer protection 

Lab trials last year illustrated the importance of dose rate for maximising the longevity of rust protection, especially when varietal resistance is compromised. 

The trial compared a resistant variety (non-YR15) versus a variety with the YR15 gene, and examined the longevity of protection from six key rust actives (tebuconazole, prothioconazole, metconazole, azoxystrobin, pyraclostrobin, and benzovindiflupyr), applied at different rates (25%, 50% and 75% of full label dose). 

In the first 15 days after treatment, there was generally very little difference in the longevity of actives in either variety, but beyond this, differences did appear. For some actives, a much higher dose was required to give the longevity of protection required, especially when varietal resistance was compromised. Generally, strobilurins and the SDHI (benzovindiflupyr) gave the longest-lasting effects, even at lower doses. 

It is worth noting that 15 days is in the middle of the circa four-week T-timing interval, supporting the potential need for an interim spray to protect any new leaves emerging between the main treatments. 

Early drilling risk? 

Traditionally, early drilling is seen to favour septoria, while later drilling favours rust; the reason being that later-sown crops are less mature, so their resistance is less capable when rust comes in. 

With many wheats drilled early last autumn, septoria risk may well be higher, however if a variety’s yellow rust resistance is compromised, then rust risk could also be greater, as crops are likely to have more biomass and will have been in the ground longer to capture spores. 

Cold weather during January may have reduced pressure, but to what extent is always challenging to predict until we get to spring. Prolonged cold is likely to have slowed and delayed rust arrival in crops, however it is unlikely to have gone completely. Higher soil nitrogen may further increase disease risk, especially where large first doses are applied.

Another implication of early drilling is to extend the phyllochron – the gap between leaf emergence – which poses challenges for traditional ’T’ fungicide timings, designed around septoria management and its 360 day-degrees latent period. Yellow rust in contrast, operates on a much shorter timeline, nearer 180 day-degrees, so there may be a need for interim sprays, such as a T1.5, in higher-risk crops. 

Six steps for managing early disease pressure

1. Identify disease risk for every field, considering variety, drilling date, and weather
2. Act early to prevent disease populations building
3. Focus early sprays on yellow rust, but don’t overlook septoria or mildew if pressure is high
4. Use chemistry wisely to its best effect
5. Use an appropriate dose to control disease present and maximise protection to the next treatment
6. Plan for shorter intervals/ interim sprays to maintain effective control where variety resistance is compromised and rust pressure is high.

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