Efficacy of methyl iodide and synergy with chloropicrin for control of fungi

Efficacy of soil fumigation with methyl bromide and methyl iodide against B otrytis cinerea, Colletotrichum gloeosporioides, Fusarium oxysporum, Gliocl adium virens, Phytophthora citricola, Phytophthora citrophthora, Pythium ul timum, Rhizoctonia solani and Verticillium dahliae was determined in labora tory experiments in closed fumigation chambers. Pythium ultimum was the mos t sensitive fungal species with EC50 values for methyl bromide and methyl i odide of 15.5 and 8.6 mu M, respectively. R solani was the least sensitive with EC50 values of 253.4 and 161.4 mu M for methyl bromide and methyl iodi de, respectively. Relative potency ([methyl bromide]/[methyl iodide]) value s ranged from 5.2 for P citricola to 1.5 for F oxysporum. Methyl iodide was 2.7 more efficacious than methyl bromide averaged over all fungal species. Methyl bromide/chloropicrin and methyl iodide/chloropicrin applied jointly were 2.2 and 2.8 times more efficacious, respectively, against F oxysporum than when the compounds were applied singly. Combining methyl bromide and methyl iodide with chloropicrin resulted in a significant synergistic incre ase in activity against F oxysporum. (C) 2000 Society of Chemical Industry.