Potato growers and agronomists should be mindful of developing blight strains less sensitive to fluazinam, but selective use and active planning can effectively preserve the full benefit of Shirlan for tuber blight protection at the season end.
Syngenta technical manager, Douglas Dyas, highlighted the blight zoospore control of Shirlan made it a crucial component of the programme, particularly at the end of the season. “However, with the reported increasing incidence of EU-37 (Dark Green 37) that has shown to be less sensitive to fluazinam, it is important growers and agronomists adapt blight programmes now to minimise the risk of further spread.”
He advocated growers use alternative blight actives for foliar blight applications through to desiccation, alternate actives in the programme, or mix another active with the fluazinam treatments – such as cymoxonil or mancozeb, or better still both – particularly under high pressure situations.
“EU-37 has shown no insensitivity to mandipropamid, or other actives, so a programme including Revus or Amphore Plus will maintain full efficacy and limit the potential for the strain to develop. Fully protecting the foliage from blight is still the best way to minimise risk of infection spreading to tubers.”
Where EU-37 has been kept out of crops through the growing season, there is less risk for using fluazinam to protect against tuber blight at desiccation.
Mr Dyas added that where full blight programmes have been used the Green 33 blight strain, that has also shown reduced sensitivity to fluazinam, appears to have been effectively managed, with the population maintained at negligible levels in the UK.
Monitoring blight strains in mainland Europe suggests that EU-37 is “fitter” and has benefitted from selection advantage where fluazinam has been very widely used in programmes, he reported. “It was observed in several sites in the UK last year, and would appear to becoming more prevalent.
“Implementing the resistance management recommendations now could avoid problems with disappointing efficacy, whilst also preventing the further rise in prevalence of EU-37.”
Douglas’ Top Tips for Tuber Blight protection include:
- Maintain blight programmes right through to lifting; don’t stretch intervals
- Use Shirlan at the full rate and always alternate with other zoospore active fungicides.
- Desiccate crops quickly and completely with Reglone – targeting rapid leaf removal and follow-up stem kill
- If flailing crops, always apply Shirlan, or an alternative zoospore active fungicide, before – and include in any follow-up stem kill application
- Allow good skin-set prior to lifting