Soil Fumigation with Dazomet and Methyl Bromide for Control of Corky Root of Iceberg Lettuce. R. Douglas O’Brien, Department of Plant Pathology, University of California, Davis, CA 95616. Ariena H. C. Van Bruggen, Department of Plant Pathology, University of California, Davis, CA 95616. Plant Dis. 74:1022-1025. Accepted for publication 29 June 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-1022.

In microplots (1.5 × 2 m) at Davis, CA, soil fumigation with dazomet (450 kg/ha) and methyl bromide + chloropicrin (500 kg/ha) controlled corky root of iceberg (crisphead) lettuce (Lactuca sativa) caused by Rhizomonas suberifaciens. At harvest, the plant disease scores were 25–50% lower and shoot and root dry weights were 40 and 33% higher, respectively, in fumigated plots than in nonfumigated controls. Similar results were obtained in a larger field experiment at Salinas, CA, in which dazomet (200 or 400 kg/ha) and methyl bromide + chloropicrin (400 kg/ha) were compared with a nonfumigated control. One month before harvest, plants from control plots had disease severities 3.6 times greater than plants from plots treated with dazomet at 400 kg/ha or methyl bromide + chloropicrin at 400 kg/ha. Head weights (untrimmed) from plants grown in plots treated with dazomet at 400 kg/ha and methyl bromide + chloropicrin at 400 kg/ha were 39 and 52% higher, respectively, than those from control plots. Application of dazomet at 200 kg/ha resulted in insignificant control of corky root.