April 24, 2017
Septoria Management Priorities
Managing Septoria resistance is fast-becoming the most critical priority in wheat fungicide choice today, stresses Agrii head of technical, Clare Bend.
Strobilurins ceased to be effective against Septoria from 2002. We’re continuing to lose curative activity from triazoles every year. And resistance to the SDHI’s on which we increasingly rely for control has now been confirmed in several parts of the UK.
Although one highly resistant strain of Septoria tritici (CH152R) is particularly worrying, the best scientific evidence suggests SDHI resistance is unlikely to develop as rapidly as strobilurin resistance. Equally, though, its progression doesn’t look like being as gradual as it continues to be with triazoles.
There’s some exciting new chemistry active against resistant Septoria on the horizon. But we won’t have it in our toolbox until 2019/2020 at the earliest. So we need to do everything we can to protect our existing tools to keep on top of this ubiquitous disease.
Our challenge is complicated by the fact that a lot of resistance can develop within a single season as field Septoria populations change in response to the chemistry we employ. To minimise this risk we have to adapt our fungicide programmes through the season as well as using the most appropriate combinations and formulations of actives at each stage.
Triazoles will continue to be the cornerstone of our defence, as much to protect the SDHIs as for their own activity. Our extensive research shows straight repeated epoxiconazole programmes no longer give worthwhile septoria control so we need to ring the changes.
In contrast, by tackling different strains in the population to restrict the selection pressure for resistance, stacked azoles are typically giving us an extra 0.4 – 0.8 t/ha wheat yield in trials. Alternating azoles between treatments can be valuable too.
We have to stack and sequence them correctly, though. Many Septoria strains resistant to epoxiconazole may also be resistant to prothioconazole. Yet the pattern of cross resistance with metconazole or tebuconazole is nowhere near as clear cut.
The multi-site protectants, chlorothalonil (CTL) and folpet remain vital in our Septoria management. There’s no known resistance to either active and both are proven to reduce the selection pressure on triazoles.
On the other hand, it’s important to appreciate that they are only protectants, will only work for as long as they remain on the leaf surface and can do nothing to tackle infections that have already taken place.
The continual decline in curative activity with triazoles and the need to protect SDHIs means our approach to Septoria control these days has to be primarily preventative. That’s why, following extensive recent research, we’ll be using SDHIs at both T1 and T2 in many cases this season.
We recorded a 0.75t/ha yield reduction from only employing an SDHI at T2 in our trial work last season. And this in a robust four spray programme work with one of the most Septoria resistant varieties available, Solace.
It could be argued that successive SDHI applications will increase the selection pressure for resistance. But without the most effective control at T1, the need for curative action at T2 is likely to be immense – and with it the pressure on the chemistry. So two SDHIs looks like being the best approach; all the more so for their value in protecting triazoles.
Having two additional SDHI products in our toolbox this season – Solatenol (benzivindiflor) and Ascra (bixafen + fluopyram) – gives us useful extra flexibility here.
The strong brown rust activity Solatenol has shown in our trials makes it an attractive proposition for varieties like Crusoe. And the double SDHI, Ascra is certainly better on Septoria than bixafen + prothioconazole at T2.
Having said that, neither has given us any yield advantage over our favoured combination of epoxiconazole, metconazole and fluxapyroxad. Where we use Solatenol too, it will be in a twin pack with chlorothalonil, rather than as the co-formulation so we have the flexibility we need to adjust the triazole component.
Overall, this season we strongly advise using multi-sites at T0, T1 and T2 with stacked and sequenced triazoles throughout and SDHIs at both T1 and T2. Where Septoria pressures are particularly high, a CTL at T1.5 to protect Leaf 2 may also be valuable.
Alongside this, our research shows the value of tailoring product choice and rate to variety and sowing date as well as weather conditions. It highlights the importance of making any economies towards the end of the season rather than early on. And, though it certainly can’t replace a fungicide, it underlines the value of appropriate micro-nutrition in maximizing performance through healthier crops.
What’s more we know it works in commercial practice. Last season, for instance, our fungicide approach with a crop of KWS Lili delivered 11.51 t/ha in field scale trials compared to 10.56 t/ha from a parallel four-spray farm standard regime to deliver an extra margin of £80/ha.