AHDB: Why the RL fungicide programme is commercially relevant

Date:12-25-2024

Do you sometimes wonder why a ‘belt-and-braces’ fungicide programme is used in the RL treated trials? Paul Gosling, who leads the Recommended Lists (RL) project at AHDB, explains how the approach is closer to commercial practice than you may think.

The perceived issue

In theory, there is nothing to stop the commercial use of the RL fungicide programme. After all, it is compliant with all regulations. But there is one big reason why it will never reflect commercial practice – cost.

Take the fungicide programme in the RL winter wheat trials, where the average cost is about £260/ha. Contrast this with the average cost of a wheat fungicide programme from the John Nix Farm Management Pocketbook, which comes in at less than half of that (at £116/ha in 2024).

It is easy to conclude that RL fungicide treated yields are not relevant in practice.

Why are RL treated yields high?

Clearly, RL fungicide treated trial yields are elevated compared to typical commercial yields. For example, the average winter wheat fungicide treated control yield (2020–2024) in the RL trials is 10.8 t/ha – far higher than the five-year average commercial wheat yield of 7.3 t/ha (based on the most recent Defra survey data).

There are many reasons for RL fungicide treated crops having relatively high yields and the fungicide programme is only one. For instance:

• We avoid fields with obvious problems (such as weedy fields)

• We sow trials in the best parts of the fields (for example, to avoid compacted headlands)

• We discard unrepresentative plots (for instance, plots that establish poorly or are damaged by pests)

• Plot edges benefit yields (plants at plot edges grow better because there is less competition for water, nutrients and sunlight)

Is it better to think about margins?

It is easy to obsess about yield, but is that the best way to think about success? Certainly, feedback from recent RL reviews indicates that farmers increasingly care about other metrics, especially crop margins.

A few seasons ago (2019–2021), the AHDB/ADAS wheat fungicide margin challenge set out to achieve just that. On a mission to get the best crop margin at each regional trial site, farmer entrants designed fungicide programmes for a single (locally relevant) variety, which they tweaked throughout the season based on site disease pressures. All other inputs were standardised.

The programmes were applied to fully randomised plot trials (three replicates). All spray timings were the same (T0, T1, T2 and T3); only products and rates varied between competitor programmes. Not all competitors sprayed at each timing (some skipped T0).

The sites also included fungicide ‘untreated’ and ‘blockbuster’ plots, with the latter based on the RL fungicide programme to establish yield potential.

The initiative yielded interesting results that help put the RL fungicide programme in context.

Here are the main results for three regions in the final year of the challenge (2021 data).

West

The RL spray programme yielded 10.73 t/ha, 1.83 t/ha above the untreated plots. This is typical for the variety grown (Graham), which has moderate levels of disease resistance. The average yield from the commercial programmes was 10.30 t/ha, and had an average fungicide spend of £82.04.

However, the highest margin was from £79.54 spend, with a yield of 10.62 t/ha – just 0.11 t/ha below the RL treatment yield.

East Anglia

The RL spray programme yielded 10.98 t/ha, 3.86 t/ha above the untreated plots. This is about as expected for the yellow-rust-susceptible variety grown (Skyfall). The average yield from the commercial programmes was 10.01 t/ha, and had an average fungicide spend of £79.68.

However, the highest margin was from £114.70 spend, with a yield of 10.76 t/ha – just 0.22 t/ha below the RL treatment yield.

North East

The RL spray programme yielded 12.07 t/ha, 3.63 t/ha above the untreated plots. This is typical for the variety grown (KWS Parkin). The average yield from the commercial programmes was 10.76 t/ha, and had an average fungicide spend of £97.10.

However, the highest margin was from £115.15 spend, with a yield of 12.04 t/ha – just 0.03 t/ha below the RL treated yield.

Margins matter

On average (based on the three sites mentioned above), the highest margin crops yielded just 0.12 t/ha lower than achieved in the RL fungicide programme.

Based on these trials, we can conclude that the RL fungicide programme produces yields that are similar to good farm practice.

Figure 1 shows how many competitor yields were close to the RL fungicide treated yield and those which exceeded it.

Fungicide spend vs yield

Figure 1. All commercial winter wheat yields mapped against fungicide spend (which includes application costs) in the fungicide margin challenge for harvest 2021 (the blue dots). The yields are relative to the RL fungicide treated yield, which is set at 100% (the straight green line). The broad trend for the data is also indicated (the grey curve)

In the harvest 2020 competition, disease pressure was lower and there was no statistically significant response to fungicides at two of the three sites. In 2020, even more commercial fungicide programmes yielded higher than the RL programme.

So much spread in the approaches taken emphasises why it is extremely difficult to pick a fungicide programme that could represent the ‘farm standard’ in RL trials. Even if a single price point is picked, it results in a vast spread in the yields achieved − and that is with just a few varieties. In RL trials, we deal with dozens of varieties, with different strengths and weaknesses.

Beyond the fungicide margin challenge, it is worth noting that the current world record wheat yield is 17.96 t/ha – far above the RL average yield (this record was set in Lincolnshire in 2022, in a system targeting yield potential).

Why use such an intensive programme?

Yes, the RL programme is intensive and costly, until you consider what it does.

Ideally, we want to keep disease as low as possible in RL trials. Certainly, below 10% infection in all varieties and in all trials (although this is getting increasingly difficult to achieve).

We follow this ‘disease-exclusion’ principle to reveal the yield potential of all varieties over a range of environmental conditions, from Cornwall to Aberdeenshire, without disease confounding the results.

Aiming for yield potential tests the performance of all varieties on a level playing field.

For the fungicide programme to stand the best chance of keeping a lid on disease for all varieties in all locations, it must be comprehensive (and relatively expensive).

It means that some elements of the fungicide programme are not needed in some situations (certain varieties, locations and seasons).

To illustrate this point, let us examine the products used in the core fungicide programme for the RL winter wheat treated trials (harvest 2024).

Products used in harvest 2024 trials

T0 spray

Required: Cyflamid (cyflufenamid) + Tebucur (tebuconazole) + Comet 200 (pyraclostrobin)

Optional: Arizona (folpet)

Comments: Cyflamid is used for mildew control. Mildewicides are relatively expensive and are only likely to result in a small yield response (if any) in many situations. However, mildew can be problematic in some trials in some years, so it needs to be included to protect the most vulnerable varieties. Tebucur and Comet 200 are included to control rusts. As for mildew, their inclusion will not benefit yield in varieties with high rust resistance ratings.

T1 spray

Required: Revystar XE (fluxapyroxad and mefentrifluconazole) + Arizona + Talius/Justice (proquinazid)

Optional: Entargo (boscalid)/Elatus Era (benzovindiflupyr and prothioconazole)

Comments: It is a similar story to T0 for all spray timings. Although the T1 mix is relatively standard, it includes a mildewicide – once again, adding cost but not much yield (in most situations).

T1.5 spray

This is an optional spray that trial operators have at their disposal. Although not particularly strong, it can help get on top of rusts, with Sunorg Pro (metconazole), and septoria, with a prothioconazole product. Arizona is also an option (but it must not be used more than three times across the programme).

T2

Required: Univoq (fenpicoxamid and prothioconazol) + Arizona

Optional: A tebuconazole product/Cyflamid

Comments: The requirements at T2 include strong products (as expected for the flag-leaf spray). However, the inclusion of Arizona may not add that much extra yield.

T3

Required: Prosaro (prothioconazole and tebuconazole) + Comet 200

Optional: Arizona

Comments: The T3 timing targets fusarium species (not septoria tritici). We use Prosaro, which is also relatively expensive. We also include the Comet 200 to mop up rust on susceptible varieties. Its inclusion does not probably yield much in low rust pressure areas, such as the north of Scotland.

Lessening the intensity of the RL fungicide programme would move the trials away from a purely variety trial to a variety x fungicide trial, which would muddy the data and be far more challenging and costly to interpret.

The current approach also helps us recommend varieties that are prone to specific diseases. There are numerous examples of varieties achieving commercial success, even if they have known weaknesses in disease resistance (if managed appropriately), when they have other traits of value.

Dose notes

The disease-exclusion principle also means we use robust doses. This adds cost, but with diminishing returns, in terms of yield, in many trials. The dose effect clearly shows up in the disease control curves produced in our fungicide performance project.

Example disease control curves

Figure 2. Septoria control in a protectant situation (combined results for 2022–24), which features some of the fungicide products used in RL trials. It highlights the relatively small disease control increase associated with a move from typical commercial programme doses (half dose to three-quarters dose) to the RL programme doses (which are nearer to full dose)

Conclusions

An AHDB-funded review recently examined the RL fungicide programme. One of the conclusions of the ADAS-led work was that the current system remains the best approach to guide the selection and management of varieties, when combined with fungicide untreated yields and disease resistance ratings.

To sum up:

• The RL fungicide programme aims to control all crop diseases as much as possible

• No variety is vulnerable to all diseases

• No location has the same disease pressure

• No year will experience high pressure from all diseases

• Parts of the fungicide programme are not increasing yield for all varieties and in all locations

• The programme adds very little extra yield compared with what the best commercial programmes can achieve in normal circumstances

• Critically, the approach is fair to all varieties

• RL yield (treated and untreated) and disease resistance rating data provide the information needed to select and manage varieties