In theory, there is nothing that would prevent the planned commercial use of RL fungicide. After all, it complies with all regulations. But there is one important reason why this will never reflect business practice: cost.
Taking the fungicide programme in the RL winter wheat trial as an example, the average cost was around £260 per hectare. By comparison, the average cost of a fungicide programme for wheat in the John Nix Farm Management Guide is less than half that (£116 per hectare in 2024).
It is clear that the experimental yields from RL fungicide treatments were higher than typical commercial yields. For example, the average control yield (2020-2024) of fungicide-treated winter wheat in the RL trials was 10.8t/ha, which is significantly higher than the five-year average commercial wheat yield of 7.3t/ha (based on the latest Defra data).
RL: There are many reasons for the relatively high yields of fungicide-treated crops, and fungicide programs are just one of them. For example:
It’s easy to become obsessed with the outcome, but is that the best way to measure success? Certainly, recent feedback on the RL survey shows that farmers are increasingly concerned with other metrics, especially crop profit.
Several seasons ago (2019-2021), the AHDB/ADAS Wheat Fungicide Profit Challenge aimed to achieve this goal. To achieve optimum yield profit at each regional trial site, participating farmers developed fungicide programs for one (locally relevant) variety and adjusted them throughout the season depending on local disease prevalence. All other inputs were standardised.
These protocols are suitable for completely randomised, plot-based studies (three replicates). All spray times were the same (T0, T1, T2 and T3) with only the product and dosage different in the competing programs; Not all participants sprayed every time (some missed T0).
These plots also include ‘no fungicide’ plots and ‘heavy’ plots, the latter of which is based on the RL fungicide program to determine yield potential.
The RL spray programme yielded 10.73t/ha, 1.83t/ha higher than the untreated plot. This is typical for the variety grown (Graham), which has a moderate degree of disease resistance. The average yield of the commercial plan was 10.30t/ha, and the average cost of fungicide was £82.04.
However, the highest profit was achieved with a cost of £79.54 and a yield of 10.62t/ha – only 0.11t/ha lower than the RL treatment.
The RL spray programme yielded 10.98t/ha, 3.86t/ha higher than the untreated plot, which is what would normally be expected when growing a yellow rust susceptible variety (Skyfall). The average yield for the commercial scheme was 10.01t/ha and the average fungicide cost was £79.68.
However, the highest profit was achieved with a cost of £114.70 and a yield of 10.76t/ha – only 0.22t/ha lower than the RL treatment.
The RL spray programme yielded 12.07t/ha, 3.63t/ha higher than the untreated plot. This is typical for the cultivar being grown (KWS Parkin). The average yield for the commercial scheme was 10.76t/ha and the average fungicide cost was £97.10.
However, the highest profit was achieved with a cost of £115.15 and a yield of 12.04t/ha – only 0.03t/ha less than the RL treatment.
On average (across the three sites mentioned above), yields of the most profitable crops were only 0.12 t/ha lower than yields obtained under the RL fungicide program.
Based on these trials, we can conclude that the RL fungicide program produces yields similar to good agricultural practice.
Figure 1 shows how much competitor yields were close to the yield obtained with the RL fungicide treatment and how much competitor yields exceeded the yield obtained with the RL fungicide treatment.
Figure 1. Comparison of total commercial winter wheat production with fungicide costs (including application costs) in the 2021 Harvest Fungicide Margin Challenge (blue dots). Recovery relative to RL fungicide treatment is set to 100% (straight green line). The overall trend of the data is also shown (gray curve).
In competitive conditions during the 2020 harvest season, disease levels were low and two of the three sites had no detectable fungicide response. In 2020, even more commercial fungicide regimens yielded higher than RL regimens.
The wide range of methods used highlights why it is difficult to select a fungicide regimen that represents the “farmer standard” in RL trials. Even choosing a single price can result in huge differences in yields – and that’s just for a few varieties. In RL trials, we are dealing with dozens of varieties, each with its own advantages and disadvantages.
Apart from the issue of fungicide profitability, it is worth noting that the current world record wheat yield is 17.96t/ha, which is significantly higher than the RL average yield (the record was set in Lincolnshire in 2022 using a yield potential-based system).
Ideally, we would like to keep the incidence rate in RL studies as low as possible. Of course, the infection rate should be below 10% for all breeds and in all studies (although this is becoming increasingly difficult to achieve).
We follow this ‘disease elimination’ principle to bring out the yield potential of all varieties in a range of environmental conditions from Cornwall to Aberdeenshire, without disease influencing results.
For a fungicide program to provide maximum control of all diseases in all regions, it must be comprehensive (and relatively expensive).
This means that under certain circumstances (certain species, locations and times of year) certain elements of the fungicide program are not required.
To illustrate this point, let’s look at the products used in the core fungicide program in the RL winter wheat treatment trials (2024 crop).
Comments: Cyflamid is used to control mildew. Mildew inhibitors are relatively expensive and in many cases are likely to have only a minor effect on yield. However, in some trials mildew may cause problems after a few years, so it is necessary to include it to protect the most vulnerable varieties. Tebucur and Comet 200 are used to control rust. As for mildew protection, their addition will not improve yields of varieties with high rust resistance values.
Required: Revistar XE (fluopyram and fluconazole) + Arizona + Talius/Justice (proquinazine)
Comment: This is similar to T0 at any spray time. Although the T1 mixture is relatively standard, it does contain a mold inhibitor – again, increasing the cost, but not in large quantities (in most cases).
This is an additional spray that can be used by test operators. Although not particularly effective, it can help remove rust fungus (using Sunorg Pro) and spot fungus (using prothioconazole products). Arizona is also an option (but cannot be used more than three times in a single treatment).
Comment: T2 requirements include strong products (as expected for flag leaf sprays). However, the addition of Arizona is unlikely to result in a significant increase in production.
Comment: T3 timing targets Fusarium species (not wheat leaf spot). We use Prosaro, which is also relatively expensive. We also add Comet 200 to remove rust from susceptible varieties. In areas where rust pressure is low, such as northern Scotland, adding rust may not have much effect.
Reducing the intensity of the RL fungicide program would shift the study from testing pure variety to testing variety x fungicide, which would confuse the data and make interpretation more difficult and costly.
The modern approach also helps us recommend strains that are susceptible to specific diseases. There are many examples of strains that have achieved commercial success despite having poor disease resistance (if properly managed) but possessing other valuable characteristics.
The disease exclusion principle also means that we use high doses. This increases costs but in many studies results in lower yields. The dose effect is clearly shown in the disease control curves obtained in our fungicide efficiency project.
Figure 2. Leaf spot control with protectants (pooled 2022–2024 results), showing some of the fungicides used in the RL trials. This highlights the relatively small improvement in disease control associated with moving from typical commercial schedule doses (half to three-quarters dose) to RL schedule doses (closer to full dose).
A recent AHDB-funded review looked at the RL fungicide programme. One of the conclusions of the ADAS-led work is that, combined with yield and disease resistance ratings without the use of fungicides, the current system remains the best way to guide variety selection and management.
Post time: Dec-23-2024