Meloidogyne hapla Northern Root-knot nematode Damage to Potatoes Biology  Juveniles penetrate host roots where they establish a feeding site, developing into swollen females (cysts). The female is usually pear-shaped, with a fragile white cuticle, and may be up to 2 mm in diameter.  Ecology  Root-Knot nematodes are distributed world-wide. Symptoms  Symptoms of Meloidogyne hapla damage in potatoes include dark specks and reduced potato quality. Damage to other crops.  Meloidogyne species are also damaging pests of tomato and corn. Control.  Good control of some species has been obtained with chemicals- with fumigants generally giving better control than granular nematicides.