Observations on the occurrence, pathogenicity and control of Pratylenchus vulnus, P. thornei and Xiphinema diversicaudatum associated with glasshouse roses

About half the nurseries and glasshouses in the Lea Valley of Hertfordshire were found to be infested with either or both Pratylenchus vulnus and Xiphinema diversicaudatum. The latter nematode probably occurred naturally in the soil on which the glasshouses were built but P. vulnus is thought to have been imported with rose rootstocks and is not known to occur outdoors in Britain. Both nematode species can cause decline of roses and even small numbers seem harmful. Numbers of P. vulnus can increase greatly, especially on rootstocks of Rosa canina, although numbers were often smaller when roses were severely damaged than on healthier crops. Numbers of X. diversicaudatum increased more slowly and R. canina was a better host for it than R. chinensis. X. diversicaudatum seemed to respond less quickly than P. vulnus to reduced host-plant vigour. The two rootstocks exhibited different host-status for the two species of nematode and cuttings of various rose cultivars showed different host-status to P. thornei, another species of lesion nematode which is not known to be pathogenic to roses. Two applications of dibromochloropropane liquid at the rate of 70 l/ha in a large volume of water maintained nematode densities at an acceptably low level, and growers who adopted this treatment as a supplement to pre-planting steam sterilisation and/or DD (dichloro-propane: dichloropropene) prolonged the productive life of their crops for several years.