Efficacy of copper oxychloride base fungicides to control cucumber downy mildew in greenhouse conditions in Iran

The use of a multi-site fungicide in cucumber downy mildew protection programs are recommended to ensure crops are adequately protected and delay a possible resistance development of high-risk groups of single-site fungicides. Commercially available dicopper chloride trihydroxide (also known as copper oxychloride) based fungicides (M FRAC Group) were assessed for their efficacy against cucumber downy mildew in comparison to a commonly used phosphonate (Fosphite® 53 WSL, P7 FRAC Group) and untreated control. Foliar treatments started with the onset of disease symptoms and were repeated weekly. Disease severity was calculated twice during crop development. Significant differences between the treatments were detected. Fosphite® was the most effective among other treatments, with a reduction in disease severity of 82.6%. Among the copper oxychloride-based fungicides, statistically significant differences were detected. Copertox® and Oksavit® were significantly effective than the other products at the first disease assessment, and Copertox® being the most efficient fungicide at the second disease assessment. Significant differences were also detected among control plots. The efficiency of commercial brands of copper oxychloride in control of cucumber downy mildew was 53-67%. This efficiency is acceptable in normal disease conditions but not desirable in an epidemic situation. If the conditions are favorable for a severe disease epidemic, it is necessary to combine them with more effective fungicides such as Fosphite.