Resistance to crop chemicals is becoming a growing problem in many areas, with SDHI mutant strains in septoria, net blotch and ramularia, being found at UK trial sites.

At last week's AHDB/SAC Agronomy Scotland Conference, in Perth, cereal growers were urged to rethink their chemical use strategies to take account of the problem.

SRUC's crops specialist, Professor Fiona Burnett, said that while SDHIs remained highly active, there is ‘a bit of a wobble and a decline in efficacy,’ and a need to rethink their use to avoid further mutant strains developing.

Instead, she encouraged producers to take advantage of low risk situations, pointing out that less septoria is generally found in late sown and resistant variety crops and in low seed rate crops. Low rainfall in spring also often reduces septoria pressure.

To control septoria she said Elatus Era, Librax, and Ascra were all comparable for protection and azoles and multi-sites can be used to slow resistance development.

The SDHIs and azoles have also shown poor efficacy in UK trials to reduce ramularia levels in both winter and spring barley crops. The disease, which was found in epidemic proportions last year, can still be treated with chlorothanlonil.

For net blotch in barley, mixed products have been shown to give best efficacy with Comet still found to be beneficial. The other big disease found in barley, rhynchosporium, is best controlled with Priaxor, Elatus, Era or Siltra Xpro with good control with the use of Proline or Imtrex.

Cyflamid is proving to be the most effective of the specific mildwicides with prothiocanzole also effective, with SDHIs adding to 'efficacy'.