Control of Soilborne Pathogens of Zingiber officinale by Methyl Iodide and Chloropicrin in China.

Development of effective alternative soil fumigants is essential to the phasing out of methyl bromide (MeBr) while keeping major soilborne pathogens under control. Here, we report on the laboratory studies and field trials evaluating methyl iodide (MeI) and chloropicrin (Pic) for control of major soilborne ginger (Zingiber officinale) pathogens Ralstonia solanacearum, Pythium spp., Fusarium oxysporum, and Meloidogyne incognita in Shandong province of China. Laboratory studies indicated that MeI at 24 mg/kg of soil was most effective, reducing four pathogens by >90%. Treatments with MeI+Pic at 12 mg/kg (1:3 and 1:5) also reduced these pathogens by >82%. In the field trials, MeI at 30 or 40 g/m and MeI+Pic (1:3) at 40 g/m yielded excellent long-term control of all target pathogens. These treatments allowed ginger plants to maintain vigorous growth and produce a greater number of tillers (>12 per plant), and increased ginger yields by >80% compared with the nontreated controls. MeI at a reduced rate of 20 g/m or Pic at 40 g/m provided levels of disease control similar to MeBr. These studies demonstrated that injection treatments with MeI at 30 and 40 g/m, and MeI+Pic (1:3) at 40 g/m, followed by covering with virtually impermeable film, are effective alternatives of soil fumigation for control of the major ginger pathogens in Shandong.