Rays of light in the fungicide performance update for 2019

When it comes to the annual fungicide performance update for cereals and oilseed rape, fungicide resistance and restricted chemistry are familiar tales. However, the 2019 instalment had a relatively upbeat tone.

This year, it was the turn of Jonathan Blake (ADAS) to outline the trends in the performance of fungicides at the AHDB Agronomists’ Conference (2 December 2019).

Much-needed new and promising products featured in the fungicide performance curves this year. These products bring welcome efficacy and flexibility to spray programmes at a time when key chemistry is due to be lost to industry – most notably the multisite chlorothalonil (CTL).

In terms of fungicide resistance, the 2019 data show that shifts in fungicide insensitivity do not appear to be as extreme as in recent years – with evidence of a potential stabilisation in key fungal species.

This article outlines some of the key moments from the 2019 fungicide performance update.

Following a period of relative stability (2008–15), early season monitoring detected significant shifts in sensitivity to SDHIs within septoria populations between 2016 and 2018. The revelation provided a wake-up call for industry. Thankfully, there was little evidence of a further significant shift in 2019. It appears that loss of control, reported at some commercial sites in 2019, was probably due to disease pressure, rather than a shift in the pathogen population. Similar monitoring of azoles also showed that insensitivity shifts in septoria tritici populations could be levelling off.

However, the apparent stabilisation in fungicide sensitivity in septoria populations does not mean the industry can relax. The long-term trend shows a gradual decline in SDHI/azole efficacy and it remains essential to follow resistance management guidelines.

Fungicide performance trials provide the toughest of tests for chemistry. Trials are set up in areas known to be at high risk from septoria tritici and the varieties chosen are relatively susceptible (e.g. disease ratings of 4–5). A single spray – at quarter, half, full or double dose – is applied at a range of fungicide timings to provide a good spread of protectant and curative data.

The UK agrochemical manufacturing industry also supplies fungicides in their development phase, so we can release performance information upon registration. The 2019 update included information (three years in trial) on the newly released product Revystar XE. This contains a new triazole (mefentrifluconazole) and an established SDHI (fluxapyroxad) and has approval for a range of cereals.

In trials, the new product performed well against septoria tritici. It also provided a positive yield response up to full label dose. At the conference, Jonathan said: “Revystar XE provides a step up in terms of activity, compared with the other azole/SDHI products in trials.”

Figure 1. Yields recorded in septoria tritici fungicide performance trials (2017–19, 20 trials): Active ingredient mixtures (left-hand chart) and straights (right-hand chart) shown

The fungicide performance for wheat update also includes activity against yellow rust, brown rust, powdery mildew and fusarium.

Robust fungicide programmes have put greater selection pressure on disease pathogens, making the appearance of resistance to fungicides more likely. In barley, ramularia is currently of greatest concern, with shifts in sensitivity to strobilurins, azoles and SDHIs detected in UK populations.

Fungicides that have multisite modes of action are much less prone to resistance. Of these, CTL is considered most effective against ramularia. Current advice is to include it where a T2 fungicide is applied. However, all CTL-containing products will expire by 20 May 2020. This will create some gaps in the 2020 spray programme (e.g. some spring barley in Scotland) and significant gaps (i.e. all conventionally produced barley across the UK) from 2021 onwards.

Bravo (CTL) was included in the 2019 fungicide performance trials and tested alongside Revystar XE and Proline (prothioconazole). CTL has been popular because it provides very high levels of control against ramularia. However, both Proline and Revystar XE have shown useful activity in trials. This activity will become more essential after CTL is lost. Farmers will need to consider how to adapt spray programmes, which will require a thorough assessment of the costs and benefits. The resistance situation, to both azoles and SDHIs, in ramularia has not spread rapidly across the UK. Ramularia is adaptable and resistance is ‘patchy’ – facts that bring an unpredictable component to any cost-benefit analysis.

Figure 2. Ramularia leaf spot control associated with three fungicide products applied at a range of doses (2019, 2 sites)

The fungicide performance for barley update also includes activity against rhynchosporium, tan spot, powdery mildew and net blotch.

For oilseed rape, disease control is relatively straightforward, with other crop protection challenges (especially cabbage stem flea beetle control) a priority. The conference highlighted the performance of two new fungicide products:

Aviator Xpro (bixafen and prothioconazole)

Approved for control of light leaf spot, phoma stem canker and sclerotinia

Angle (azoxystrobin and difenoconazole)

Approved for phoma stem canker reduction and sclerotinia control (moderate control)

The online curves show their performance relative to established products.

Phoma stem canker summary

• Azoles, SDHIs and strobilurins all have efficacy
• Two applications providing effective control

Light leaf spot summary

• Early sown crops more at risk
• Significant yield benefits (~0.4t/ha) from control in 2019

Sclerotinia stem rot summary

• Products containing prothioconazole or boscalid lead
• Azoxystrobin also effective

Jonathan Blake (ADAS) outlined the fungicide performance trends at the AHDB Agronomists’ Conference (2 December 2019).

Watch the latest fungicide performance update. Presentation starts at 14:31.