Natural spread of this virus in orchards and nurseries results directly from transmission by nematode vectors, including the dagger nematodes Xiphinema americanum Cobb, X. rivesi Dalmasso and X. californicum Lamberti & Bleve-Zacheo. The virus can be transmitted by grafting and budding. In infested sites, the nematode and virus can persist for years on roots of infected perennial and herbaceous plants. The virus is seedborne in several weed hosts (Ogawa et al. 1995), but no mention is made of seed transmission in Malus spp.