They are only a guide. The response of varieties rarely correlates to their Recommended List rating, particularly in high pressure Septoria and yellow rust situations. So it is worth combining national Recommended List data with regional, and if possible local, data to look for some consistency in results before deciding whether a variety will respond as per the Recommended List.
Even resilient varieties (low risk varieties) show regional variability to fungicide responses.
There is no way of accurately calculating the impact of drilling date on variety disease rating, but remember Recommended List data is generally drawn from plots drilled around mid-October. For any crop it’s important to be vigilant, but for wheat drilled in September or early October it is likely to be exposed to greater pressure so keep a close eye on these in particular.
Even the best SDHI fungicide is no ‘silver bullet’ against Septoria. Once the latent period is half-way through, even an eradicant fungicide is not going to fully control the disease. As mycelia is spreading inside the leaf, the next generation of infectious spores are already being formed in pycnidia (fruiting bodies), and no fungicide will be effective.
Symptoms may not be visible, but the damage is done. So if your spray timing has been compromised then it is becomes harder to reduce rates.
Can you cover your wheat area at the correct timing? The target leaf needs full protection and even the most systemic fungicides won’t protect new growth, so disease is almost certain to establish. The weather might save you – but you are in the lap of the gods.
Yield responses to fungicide inputs are not all about disease control – many modern fungicides have direct or indirect effects on the crop, Plant Growth Regulator effects, greening effects, rooting effects – many of which contribute to yield response to fungicide treatment.
If you gamble on a low disease year and it doesn’t turn out that way, NIAB TAG data shows you will lose three times the amount you ‘lose’ by spending too much in a low disease year. It is more cost-effective to spend a little too much in a low disease year than it is to spend too little in a high disease year.
The speed of Septoria development can be rapid in wet and humid conditions, and low pressure situations can become high quickly.
Also check crop winter development – can Septoria be spread by leaf contact? In recent seasons we have seen thick, lush crops in early spring due to mild conditions, which of course will favour the disease anyway.
Are you fuelling disease? YEN has shown the value in higher ears/m² and the role of early biomass in achieving this. Pulling some of your N forward to increase biomass will encourage growth and canopy development, but also disease development.
Azole and SDHI fungicides need to support each other. Are you running the risk of one being exposed through a reduced rate of a partner?
Azole performance has declined over the last 10 years but they are still useful protectants. If the azole rate is too low it will expose the SDHI partner, hastening the onset of resistance.
Developing an appropriate fungicide strategy based on disease pressure, variety, drilling date and regional factors is complex - so to help growers in this area NIAB TAG has developed a members only tool to indicate optimum programme margin over input costs.
For more information click the link below: