Evaluation of the effect of metalaxyl-M and chlorothalonil against downy mildew in cucumber and investigation of their residues

Cucumis sativus L., one of 30 cucumber species found worldwide, is the most economically significant. One of the most devastating foliar diseases of cucumbers and other cucurbits is downy mildew, caused by the fungus Pseudoperonospora cubensis. Residue levels, and degradation rate of the commercial fungicide including two active ingredients (chlorothalonil and metalaxyl-M) in the cucumber was determined with using a combination of the QuEChERS method and HPLC. Also, the effect of the fungicide is evaluated. The experiment was carried out on the cucumber crop in a greenhouse in the city of Ramadi, Anbar Governorate, eastern Iraq that designed in randomized block design. It was found to have high residue levels of metalaxyl-M and chlorothalonil in cucumbers grown in greenhouse. The fungicide required about 14 days to completely fade from the cucumber fruits. The recoveries of chlorothalonil and metalaxyl-M were 90.3 and 86.7%, respectively. The half-lives of metalaxyl-M and chlorothalonil were detected as 0.90 and 0.85, respectively.