Pratylenchus spp. andVerticillium spp. in New Brunswick potato fields

A survey of New Brunswick potato fields with symptoms of early dying was conducted in September 1990 and 1991. Root lesion nematodes (Pratylenchus spp.) were detected in 43 of 46 fields in 1990 and in 37 of 43 fields in 1991. In 1990 and 1991 populations averaged 910 and 410 nematodes g-¹ dry root and 1030 and 720 nematodes kg¹ dry soil, respectively. Previous crops did not affect nematode populations, except in one comparison where the number of nematodes in potato roots in 1990 was higher when the previous crop was cereal than in 1991 when the previous crop was peas.Pratylenchus crenatus was more prevalent thanP. penetrans. Root-knot nematodes(Meloidogyne hapla) were detected at a few sites at low population levels only in 1991. In 1991,Verticillium albo-atrum was detected in all 37 potato fields where fungal analyses were conducted, and the average population was 350 propagules g¹ dry soil. Soil populations ofV. alboatrum did not differ in fields in which either Russet Burbank or Shepody were being grown, nor did previous crops have any effect.Verticillium dahliae was detected in 17 fields at very low populations, usually below 1 propagule g¹ dry soil. There were no significant correlations (P<0.05) between populations of P.crenatus orP. penetrans in soil or roots and populations ofV. albo-atrum orV. dahliae propagules in soil.