See:
Apple (Malus spp.) - Nematode, Dagger
Apple (Malus spp.) - Nematode, Root-lesion
Notes: There are many nematode problems in the Pacific Northwest including dagger and root lesion nematodes. However, there has not been any published or concentrated effort to document nematode problems in pear orchards in Washington or Oregon. Few samples from pear orchards have come into the OSU Nematode Laboratory. It is suspected that nematodes are a problem on pear that simply has not been investigated.
An unpublished study in eastern Washington in the early 2000's found that root lesion nematode populations were statistically highest in pear (OldHome) and M.26 (apple) rootstocks and lowest in peach rootstocks when compared across apple (G.16 and M.26), cherry (Giesla, Mahaleb, and Mazzard), and peach (Citation and Nemaguard) rootstocks. Compendium of apple and pear diseases (2014) indicates that apples are more sensitive to root lesion nematodes than pear but notes that pears are usually planted on heavier soil which can sustain high populations without causing as much damage.
Black line disease (apple union necrosis) of pear graft unions caused by tomato ringspot virus vectored by dagger nematodes has been observed in the PNW.
Reference Sutton, T.B., Aldwinkle, H.S., Agnello, A.M., and Walgenbach, J.F. 2014. Compendium of Apple and Pear Diseases and Pests, 2nd ed. St. Paul, MN: APS Press.