Changes in the sensitivity of Corynespora cassiicola to fungicides on cucumber plants in Okayama Prefecture, Japan, since the 2000s

Abstract

In 2014, we collected 234 isolates of cucumber Corynespora leaf spot fungus (Corynespora cassiicola Berkeley & M.A. Curtis C.T. Wei) from 24 commercial cucumber fields in Okayama Prefecture, Japan and assessed their sensitivity to several fungicides. Among the tested strains, the proportion of thiophanate-methyl (T) highly resistant/dietofencarb (D) weakly and moderately resistant strains were 37% and 49%, respectively. Azoxystrobin (A)-resistant strains were 95%, whereas boscalid (B)-resistant strains were 39%. TD- and A-resistant strains were more widespread and more frequent than in 2000. B-resistant strains have only recently emerged.