How to use wheat varieties to reduce fungicide intensity

Ellie Dearlove examines how varieties with good disease resistance can provide greater flexibility in fungicide programmes and reduce the amount of fungicide needed.

As we approach the main cereal spray timings, we are sharing insight on disease management following a question submitted to our research ideas letterbox:

“Can reduced fungicide input levels be used to manage wheat varieties with improved disease performance? If so, how low can you go?”

The short answers are: ‘yes’ and ‘it depends on the situation’.

Varietal disease resistance is the foundation of control. The Recommended Lists for cereals and oilseeds (RL) can pinpoint varieties that offer better resistance to key diseases. For winter wheat, this includes septoria tritici, yellow rust, brown rust and mildew.

The recently launched RL interactive tool can quickly identify varieties with the highest fungicide untreated (and treated) yields. The RL variety selection tool also has a useful fungicide treatment benefit feature.

The RL has made it very easy to identify varieties with strong genetics.

Varieties with higher levels of disease resistance allow greater flexibility in fungicide programmes, including the omission of sprays and the use of reduced doses, while still maintaining acceptable yield and quality.

Even with stronger disease resistance, environmental factors, disease pressures and crop management practices influence the effectiveness of reduced-input strategies.

If varietal resistance is high, weather is not conducive to disease and fungicide applications are well-timed, lower-input approaches could help increase crop profitability.

• T0 application: In some cases, skipping T0 is feasible for resistant varieties, unless early disease pressure is high
• T1 and T2 applications: These remain crucial, especially for septoria tritici and rust management
• T3 application: The need for a T3 spray depends on fusarium and brown rust risks, as well as market requirements

There is scope to reduce fungicide doses at all spray timings. Although this includes T1 and T2, extra care is needed at these critical times.

How low you can go depends on several factors:

• Resistance ratings: The higher the disease resistance rating score (especially 7 and above), the lower the risk of unacceptable economic losses
• Weather: Wet and humid conditions tend to drive disease pressures, which may require a more robust fungicide programme
• Situation: Many farm-specific risk factors affect crop susceptibility, including cultivation, rotation, drilling date, regional disease trends and spraying capacity (attitudes to risk are also important)

Numerous AHDB research projects have examined these factors in detail, with most focusing on septoria tritici (due to the economic importance of this disease).

One study showed how sowing dates influence RL disease ratings for septoria tritici (based on an average sowing date of 7 October).

When sown early (average sowing date 22 September), the effective disease rating decreased by about 0.6. This is because crops were consistently associated with higher disease severity during the main yield-forming period.

Conversely, when sown late (average sowing date 20 October), the effective disease rating increased by 0.6.

This shows how a flexible, risk-based approach can underpin efforts to reduce fungicide inputs.

By sowing varieties with stronger disease resistance later in the autumn, there is scope to reduce the risk of a damaging septoria epidemic and enable the use of lower fungicide inputs.

The same study also examined other ways to tailor strategies to reduce disease pressure and fungicide use.

How to support crop genetics, including the use of fungicides, was scrutinised in our first Strategic Cereal Farm East, with a trial set up to compare high- and low-input programmes.

The trials used the winter wheat variety Gleam. This variety consistently gives high fungicide-treated yields across the UK (based on the RL fungicide programme, which aims to minimise the impact of all diseases).

In the Strategic Cereal Farm trial, inputs were applied at T1, T2 and T3 timings (independently and in combination) to identify the lowest practical fungicide levels.

• A tailored approach identified the best fungicides and rates

• A reduced T1 application was appropriate, but stronger chemistry was needed at T3

• When applications were skipped, it left gaps for disease to exploit

• The most expensive fungicide programme had the highest yield, but it was not the most profitable

• Generally, low-input regimes produced better gross margins

These results aligned with those recorded in the ADAS/AHDB fungicide margin challenge. However, such harvest 2020 trials generally experienced low septoria disease pressures, which favoured lower-input approaches.

In the harvest 2021 fungicide margin challenge, disease pressure was relatively high (but late) and moderate-to-high spend programmes produced the highest margin over fungicide costs.

To sum up, using varietal resistance with other integrated pest management (IPM) approaches, such as monitoring, forecasting and agronomic practices, will help you protect crops. It will also help you reduce fungicide resistance risks.

Our fungicide performance data, which shows at-a-glance information on the relative efficacy of key fungicide products, can also help you select fungicides and assess the potential to lower doses.

Farming is full of questions. We will always do our best to provide independent and evidence-based answers.

Some may be based on readily available information. Others may need further investigation in our research programme.

So, whether you are wondering about the latest research, looking for practical on-farm solutions or have a burning question about our work, send it our way, via the research ideas letterbox.