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Shift in septoria sensitivity to key fungicide chemistry The AHDB Agronomists’ conference provided the platform for the latest fungicide performance results to be presented and discussed, including confirmation of the discovery of a number of less sensitive septoria isolates to SDHI chemistry. Dominic Kilburn writes. SDHI fungicides are still providing a good level of performance against septoria in winter wheat but there is some evidence of a decline in efficacy. That was one of the key messages provided by ADAS’ Jonathan Blake (right) speaking at the AHDB Agronomists’ conference prior to the Christmas break. However, the news that the decline in triazole efficacy in a protectant situation had, over the past four years somewhat slowed, was encouraging, he stated. Dr Blake suggested that up until 2015 it was unlikely that there had been much of a change in SDHI efficacy in relation to septoria, however, in 2016, there was a “wobble” where a few less sensitive septoria isolates had been found. And then, in 2017, laboratory tests confirmed that a considerable number of less sensitive septoria isolates had been discovered – significantly more than had been seen prior to 2015. “It does seem that there is a percentage of the septoria population that is less sensitive than it used to be,” noted Dr Blake. “We are seeing this shift in sensitivity in the field and in the lab, and the same is being found in Ireland,” he added. He said that in 2013 trials, half and quarter rate performances in SDHI Imtrex (fluxapyroxad) gave around 90 per cent control of septoria and now, on average, it was nearer 50-70 per cent control. “The lower rates seem less effective than in the past and so to achieve those higher rates of control, we may need to use increased rates of SDHI,” he said, pointing out that similar patterns were seen in trials with Vertisan (penthiopyrad).

Dr Blake highlighted 2017 data from an on-going AHDB project (looking at resistance management and the best way to protect future modes of action), and said that the more we use SDHIs, then the quicker we select for insensitivity – particularly with the addition of a second SDHI fungicide in a programme. So only applying SDHIs when really needed, along with good resistance management, including use of multisite products, should help to prolong their efficacy. “By adding a multisite fungicide we’re able to bring the mutant strain frequency down a bit,” he added.

Azole stability Dr Blake suggested that increased use in mixtures of SDHI and multisite products in recent years may have played a part in the stabilising of septoria populations where triazoles are concerned. “Both in protectant (50 per cent control) and curative situations (20–40 per cent control) there has been little change in efficacy since 2012/13. “It’s a huge shift from where we were originally with these products but we aren’t seeing rapid changes in azole sensitivity now,” he added.

2017 protection Running through the AHDBfunded trials results focusing on specific fungicide performance in wheat, Dr Blake said that both Ignite (epoxiconazole) and Proline (prothioconazole) performed similarly to each other in a protective situation during 2017. This is a slight change from the 2016 season when prothioconazole was looking slightly stronger, he noted. SDHI single actives Imtrex and

Vertisan provided reassuringly higher protection on average against septoria across all (five) sites and this didn’t represent a change from 2016. According to Dr Blake, Bravo (chlorothalonil) at the half dose rate in a protective situation provided 50 per cent control of septoria – more than Ignite or Proline at their full label rates – and added that chlorothalonil is a very important part of protecting crops. SDHI mixtures Elatus Era (benzovindiflupyr + prothioconazole), Librax (fluxapyroxad + metconazole) and Ascra Xpro (bixafen + fluopyram + prothioconazole) all performed very well in 2017 at full label rate, and couldn’t be separated in terms of their performance. Looking at performance against septoria over three years, results showed a similar pattern to the one-year data with the exception of prothioconazole and the SDHIs performing a little stronger in comparison. Aviator Xpro (bixafen + prothioconazole) was not quite as strong as Ascra Xpro, however. In septoria curative performance for 2017, azole prothioconazole came in a little stronger than epoxiconazole at the higher rates, Elatus Era and Ascra Xpro performed well and similar to each other, and Librax even better – which Dr Blake described as a ‘seasonal effect’. Over three years, all SDHI mixes had similar curative activity with Librax being stand out in 2017. Focusing on yield, broadly, the

There is a percentage of the septoria population that is less sensitive to SDHI chemistry than it used to be.

SDHI mixes performed the same with Elatus Era a little better in terms of persistence, said Dr Blake and, while it was difficult to separate yield performance over three years, he suggested that fluopyram in Ascra Xpro gave that product a yield advantage over Aviator Xpro.

Rusts Although yellow and brown rust in wheat may not be the key worry for growers over winter months, due to colder weather keeping them in check, Dr Blake suggested that, in milder conditions and with a high number of wheat varieties showing susceptibility to the two diseases, they are ones to watch. Most products in yellow rust trials performed similarly well in continued over...

AHDB trials – Wheat fungicide performance at a glance Septoria: SDHIs are still providing a good level of performance against septoria but there is some evidence of a decline in efficacy. Elatus Era, Librax and Ascra Xpro SDHIs are all comparable for protection. Use azoles and multisites to slow resistance development. Rust: Epoxiconazole is still a lead azole and highly effective in curative situations. Pyraclostrobin showed good activity especially on yellow rust. New SDHI Elatus Era highly effective on both rusts. Fusarium: Prothioconazole leads but metconazole, tebuconazole and epoxiconazole are all close behind.

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