Preplant soil fumigation for control of violet root rot of carrots

Abstract

Violet root rot (VRR) caused by Rhizoctonia crocorum causes substantial economic losses and threatens the longterm viability of the carrot industry in the Ohakune region New Zealand Previous attempts at control have been largely unsuccessful Pre planting soil fumigation trials were carried out in two heavily infested Ohakune carrot fields In 2007/08 chloropicrindichloropropene (TriForm 60) and metam sodium (Fumasol) failed to provide a commercially useful level of VRR control Deficiencies in fumigant placement and distribution and inadequate sealing of the soil for gas retention were identified as likely reasons for the failure Modified application techniques improved soil sealing and different combinations of fumigants in the 2008/09 season provided excellent control in some treatments At Site A VRR incidence was 06 and 667 in the chloropicrinmetam sodium and chloropicrin treatments respectively compared with 986 incidence in untreated control plots At Site B VRR incidence was 23 and 38 in the chloropicrindichloropropene and combined chloropicrindichloropropene metam sodium treatments with and without plastic covering respectively compared with 415 in untreated control plots