Do not plant Irish potatoes after beets, carrots, radishes, parsnips, rutabagas and turnips, which are also susceptible to scab. Use certified seed pieces that are resistant to scab. Alamo, Cascade, Cherokee, La Rouge, Lemhi, Nooksack, Norchip, Norgold Russet, Norland, Onaway, Ontario, Plymouth, Pungo, Russet Burbank, Shurchip, Sioux, Superior and Targhee. There is no reliable chemical control. Root knot is caused by the southern root-knot nematode, Meloidogyne incognita .
Nematodes are microscopic worms that live in the soil.
They are not related to earthworms. Nematodes feed on plant roots, damaging and stunting them. The first evidence of a nematode problem is poor growth of plants and poor color of foliage. The damaged roots cannot supply sufficient water and nutrients to the aboveground plant parts, and the plant is stunted or slowly dies. Symptoms are more pronounced during dry weather.